Oil, too thin? Too thick? Bearing?
25 August 2010, 07:40 PM
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Oil, too thin? Too thick? Bearing?
I've done a search but not found the answer's I am looking for, right, I have a
1997 uk turbo on 130,000 ish miles, 300bhp, I was running motul 15w 50 fully synthetic, but was told that, that was way to thick for my car, mainly from,
cold, I am now down to a 5w40 silkolen oil, now I have been told by my
mapper that I need a 15w 50 to protect the big end bearing or was it main
thrust bearing?, as with a thin oil it won't be lubricated enough, can
someone clear this up for me? Only just had the oil changed as well!
Thanks
1997 uk turbo on 130,000 ish miles, 300bhp, I was running motul 15w 50 fully synthetic, but was told that, that was way to thick for my car, mainly from,
cold, I am now down to a 5w40 silkolen oil, now I have been told by my
mapper that I need a 15w 50 to protect the big end bearing or was it main
thrust bearing?, as with a thin oil it won't be lubricated enough, can
someone clear this up for me? Only just had the oil changed as well!
Thanks
25 August 2010, 07:45 PM
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your best bet would be to use a 10/50 to cover the cold start and the hot thinning prob. silkolene do it> most would say 15 is ok ,i prefer a 10 weight cos i get less noise(pistonslap) on start up> although 10/40 is whats recommended by subaru
Last edited by Turbotits; 25 August 2010 at 07:48 PM.
25 August 2010, 07:46 PM
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would a too-thin-an oil kill it, I don't rag it much, and make sure oil is fully warmed before
taking it on boost, as you would anyway
taking it on boost, as you would anyway
Last edited by Sabas; 25 August 2010 at 07:51 PM.
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02 September 2010, 04:10 PM
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I have been reading this thread and I am astounded at what people are saying. If you want an oil recommendation you should never, ever, ever, EVER just recommend a viscosity!!!!! If you do frankly you don't know anything about oil whatsoever! Oil choice is subjective on the OPERATING CONDITIONS of an engine, that is how hot it gets, what rpm range it's mostly in on average, how many cold starts it does, the nature of the trips it does, whether it's tracked and so forth.
It has got nothing to do with a car being a 'performance' car or not, just because it's performance doesn't mean it needs a higher weight. Some use 0W-20's in their Ferrari cars. It depends on the operating conditions the engine is exposed to (it's also about oil pressure and flow).
Please!!! Tell me... people aren't putting 15W oils in cars that they use to drive round town, have the odd blat and go to tescos in! <head in hands> your recommendation is detrimental to that vehicle I guarantee it!
I have heard a lot about scaring people about Rod Bearing failures (big end or whatever you want to call it). I was curious and read around the subject, you know what I saw? People were using 0W-40 weight oils in a car where the OPERATING CONDITIONS of that engine exposed it to temps around 115 to 125C on a very regular basis. At that temperature 0W-40 is not great, I would highly recommend a (lowest you can find)W-50 oil that will be able to provide adequate protection at high temperatures. 0W-40 will not do that very well at 125C, that's probably a good reason for premature engine failure.
I will use the BMW example. I am an M5 owner, BMW 'recommend' 10W-60 for my car (not 5W-30 that some say they do, they don't call a dealer and check). Why this oil? Well it's simple, the engineers thought we need an oil that'll cope with everything the owner can throw at it, including tracking. As a consequence on a track an M5 might get to about 125C operating temperature, TWS (10W-60) is good at this temperature, it's at its best in fact. However, there is a drawback, it's protection at low temperature is worse than say a 0W-40 and not as good at temps around 80 - 95C. But BMW won't put it in because they need to cover all basis, and this should get them through their warranty period easily. I don't track my car, I drive with 'gusto' my oil temps never exceed 100C and are usually around 80 to 95C even when pushing. At this temperature range something like 0W-40 is much better, in fact I am thinking of going down to 0W-30 depending on my next oil analysis result and if I can find one that doesn't increase my consumption dramatically.
I imagine Subaru do the same, need an oil for all and because of the top end temps that the car COULD be exposed to have to have a high weight in there, something like a 10W-50. But the reality is most subaru drivers won't get temps that high, won't push the car that hard and so never get any benefit from it just the detriment of the poorer performance at their normal operating temperatures where it functions much worse than a 0W-40 oil.
Common misconceptions, oil consumption does NOT necassarily mean the oil is not suitable for the engine. The only thing you can be sure of is that it's going to be flippin' expensive to run it with that oil in. Obviously you want something you don't need to top up every 1000 miles as it gets pricey and annoying pretty quickly.
Another one, 5W-30 and 0W-30, the 0W-30 is not thinner at operating temperature, they are the same, except the 0W has a better flow rate (the important part for lubrication) than the 5W at cold start. That's better. I know what you'll say, "well why buy a 5W? why even sell it smart a$$?!" that's simple too, they're often easier to make and consumption might be lower with a 5W, people also like that it's generally cheaper.
Finally, I urge you. If you ask someone for an oil recommendation and they just blank tell you a brand and viscosity, PLEASE.. IGNORE THEM.. I need to know the operating conditions of the engine before making a recommendation that is suitable and best for your engine.
If you were going to a dyno, you are going to stress your engine and run at high temperatures, I would recommend you use an appropriate oil when doing so, but don't think for a second it's the best option for your day to day use.
There is an excellent and detailed article about oil, it explains what it is, how it works, what lubrication actually is, what figures are important and why and how to select an oil that's appropriate for you and your car. I could explain much more but I'd be writing a book and people would get bored. If you're interested mail me, be intelligent in your oil choice.
Oh and one final thing, your engine won't explode tomorrow if you now think your oil choice is wrong, don't worry, it's not a big issue just think about your next oil change.
I hope I've been helpful, oil choice is something I am very interested in and I don't want people to be misinformed. The only real way to KNOW for sure if the oil is right is to get an analysis, if you're as keen as me, do one every oil change and keep the results using them to make your next selection.
Thanks for reading
Craig
It has got nothing to do with a car being a 'performance' car or not, just because it's performance doesn't mean it needs a higher weight. Some use 0W-20's in their Ferrari cars. It depends on the operating conditions the engine is exposed to (it's also about oil pressure and flow).
Please!!! Tell me... people aren't putting 15W oils in cars that they use to drive round town, have the odd blat and go to tescos in! <head in hands> your recommendation is detrimental to that vehicle I guarantee it!
I have heard a lot about scaring people about Rod Bearing failures (big end or whatever you want to call it). I was curious and read around the subject, you know what I saw? People were using 0W-40 weight oils in a car where the OPERATING CONDITIONS of that engine exposed it to temps around 115 to 125C on a very regular basis. At that temperature 0W-40 is not great, I would highly recommend a (lowest you can find)W-50 oil that will be able to provide adequate protection at high temperatures. 0W-40 will not do that very well at 125C, that's probably a good reason for premature engine failure.
I will use the BMW example. I am an M5 owner, BMW 'recommend' 10W-60 for my car (not 5W-30 that some say they do, they don't call a dealer and check). Why this oil? Well it's simple, the engineers thought we need an oil that'll cope with everything the owner can throw at it, including tracking. As a consequence on a track an M5 might get to about 125C operating temperature, TWS (10W-60) is good at this temperature, it's at its best in fact. However, there is a drawback, it's protection at low temperature is worse than say a 0W-40 and not as good at temps around 80 - 95C. But BMW won't put it in because they need to cover all basis, and this should get them through their warranty period easily. I don't track my car, I drive with 'gusto' my oil temps never exceed 100C and are usually around 80 to 95C even when pushing. At this temperature range something like 0W-40 is much better, in fact I am thinking of going down to 0W-30 depending on my next oil analysis result and if I can find one that doesn't increase my consumption dramatically.
I imagine Subaru do the same, need an oil for all and because of the top end temps that the car COULD be exposed to have to have a high weight in there, something like a 10W-50. But the reality is most subaru drivers won't get temps that high, won't push the car that hard and so never get any benefit from it just the detriment of the poorer performance at their normal operating temperatures where it functions much worse than a 0W-40 oil.
Common misconceptions, oil consumption does NOT necassarily mean the oil is not suitable for the engine. The only thing you can be sure of is that it's going to be flippin' expensive to run it with that oil in. Obviously you want something you don't need to top up every 1000 miles as it gets pricey and annoying pretty quickly.
Another one, 5W-30 and 0W-30, the 0W-30 is not thinner at operating temperature, they are the same, except the 0W has a better flow rate (the important part for lubrication) than the 5W at cold start. That's better. I know what you'll say, "well why buy a 5W? why even sell it smart a$$?!" that's simple too, they're often easier to make and consumption might be lower with a 5W, people also like that it's generally cheaper.
Finally, I urge you. If you ask someone for an oil recommendation and they just blank tell you a brand and viscosity, PLEASE.. IGNORE THEM.. I need to know the operating conditions of the engine before making a recommendation that is suitable and best for your engine.
If you were going to a dyno, you are going to stress your engine and run at high temperatures, I would recommend you use an appropriate oil when doing so, but don't think for a second it's the best option for your day to day use.
There is an excellent and detailed article about oil, it explains what it is, how it works, what lubrication actually is, what figures are important and why and how to select an oil that's appropriate for you and your car. I could explain much more but I'd be writing a book and people would get bored. If you're interested mail me, be intelligent in your oil choice.
Oh and one final thing, your engine won't explode tomorrow if you now think your oil choice is wrong, don't worry, it's not a big issue just think about your next oil change.
I hope I've been helpful, oil choice is something I am very interested in and I don't want people to be misinformed. The only real way to KNOW for sure if the oil is right is to get an analysis, if you're as keen as me, do one every oil change and keep the results using them to make your next selection.
Thanks for reading
Craig
02 September 2010, 04:49 PM
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Sabas,
there is nothing wrong with running a 15w50 rated oil in your car, its well within what subaru recommend, but I would not run it in winter, revert to a 10w50 or a 10w40 oil for that period.
Craig, Subaru do not recommend 0 cold weight oils for their turbocharged engines, and different models can use different grades of oils, as for your BMW theory, BMW M series cars, ie the E46 M3, run very hot for a NA engined car, hence why BMW recommend a 10w60 oil for them, scoobs (even when pushed) will find it very hard to hit 120 deg C though highly modified versions can.
Please do some more investigation into which oils subaru recommend before making recommendations
Tony
there is nothing wrong with running a 15w50 rated oil in your car, its well within what subaru recommend, but I would not run it in winter, revert to a 10w50 or a 10w40 oil for that period.
Craig, Subaru do not recommend 0 cold weight oils for their turbocharged engines, and different models can use different grades of oils, as for your BMW theory, BMW M series cars, ie the E46 M3, run very hot for a NA engined car, hence why BMW recommend a 10w60 oil for them, scoobs (even when pushed) will find it very hard to hit 120 deg C though highly modified versions can.
Please do some more investigation into which oils subaru recommend before making recommendations
Tony
02 September 2010, 05:32 PM
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Tony,
I am sorry but again you've said that an oil choice is perfectly fine with no knowledge of the operating conditions of the engine whatsoever, how can you make an accurate recommendation without that information? You can't, it's as simple as that. I am not saying his car will explode and it's the worst oil possible, I am saying based on his car operating conditions this choice is poor.
I kindly offer the following:
"It is time to introduce the concept of lubrication. Most believe that pressure = lubrication. This is false. Flow = lubrication. If pressure was the thing that somehow lubricated your engine then we would all be using 90 weight oil. Lubrication is used to separate moving parts, to keep them from touching. There is a one to one relationship between flow and separation. If you double the flow you will double the separation pressure in a bearing. The pressure at the bearing entrance is irrelevant.
In fact the relationship between pressure and flow is in opposition. If you change your oil to a thicker formula the pressure will go up. It goes up because the resistance to flow is greater and in fact the flow must go down in order for the pressure to go up. They are inversely related. Conversely if you choose a thinner oil then the pressure will go down. This can only occur if the flow has increased.
High flow does more than lubricate. It is one of the things used to cool the hottest parts of your engine, the pistons, valve areas and bearings. This cooling effect is as important as lubrication in your engine. If your engine is running hot use a thinner oil. The flow will increase and so will the cooling. This is even more important in the racing condition.
More confusion occurs because people think in terms of the oil thinning when it gets hot. They think this thinning with heat is the problem with motor oil. It would be more correct to think that oil thickens when it cools to room temperature and THIS is the problem. In fact this is the problem."
I don't understand how you can possibly have an issue with a 0W oil!? At start a 0W is too thick, any oil is too thick, at operating temperature there is no difference between a 0W-40 and 10W-40, they offer the same protection. How would one be better than the other? Surely you want to protect at low temperatures more? So why would you choose the 10W over the 0W? Because someone told you?
Let's look at the 15W-50 and 0W-40 I would start with. Based on Daves use of his car, bearing in mind it's not pushed hard operating temps are about 100C at MAX, and most of the time below. It often does short trips too. Let's compare those two choices:
PRO R 15W-50
18.2 mm^2/s @ 100C
130 mm^2/s @ 40C
Mobil 1 15W-50
17.4 mm^2/s @ 100C
125 mm^2/s @ 40C
Compare that to my choice Mobil 1 0W-40 fully synth:
14 mm^2/s @ 100C
78.3 mm^2 @ 40C
From that it's clear that the Mobil 1 0W-40 offers far better protection at lower temperatures. As temperature drops both can only get worse and personally I'd rather it got worse from 78.3 than 130. Even at 100C there will be (although marginal) better flow with Mobil 1 0W-40 up to probably 110C looking at this. Beyond these temperatures a 10W-50 might be advisable if this is frequent.
So based on the facts:
1 Car does short trips
2 Car does a lot of cold starts
3 Car isn't thrashed and operating temps are around 100C at max or lower
What would your justification be for selecting 15W-50? I am genuinely interested to know.
Craig
Addition.... oh and I am gobsmacked that you'd put a 10W oil in this car in winter!? What is the logic here?
I am sorry but again you've said that an oil choice is perfectly fine with no knowledge of the operating conditions of the engine whatsoever, how can you make an accurate recommendation without that information? You can't, it's as simple as that. I am not saying his car will explode and it's the worst oil possible, I am saying based on his car operating conditions this choice is poor.
I kindly offer the following:
"It is time to introduce the concept of lubrication. Most believe that pressure = lubrication. This is false. Flow = lubrication. If pressure was the thing that somehow lubricated your engine then we would all be using 90 weight oil. Lubrication is used to separate moving parts, to keep them from touching. There is a one to one relationship between flow and separation. If you double the flow you will double the separation pressure in a bearing. The pressure at the bearing entrance is irrelevant.
In fact the relationship between pressure and flow is in opposition. If you change your oil to a thicker formula the pressure will go up. It goes up because the resistance to flow is greater and in fact the flow must go down in order for the pressure to go up. They are inversely related. Conversely if you choose a thinner oil then the pressure will go down. This can only occur if the flow has increased.
High flow does more than lubricate. It is one of the things used to cool the hottest parts of your engine, the pistons, valve areas and bearings. This cooling effect is as important as lubrication in your engine. If your engine is running hot use a thinner oil. The flow will increase and so will the cooling. This is even more important in the racing condition.
More confusion occurs because people think in terms of the oil thinning when it gets hot. They think this thinning with heat is the problem with motor oil. It would be more correct to think that oil thickens when it cools to room temperature and THIS is the problem. In fact this is the problem."
I don't understand how you can possibly have an issue with a 0W oil!? At start a 0W is too thick, any oil is too thick, at operating temperature there is no difference between a 0W-40 and 10W-40, they offer the same protection. How would one be better than the other? Surely you want to protect at low temperatures more? So why would you choose the 10W over the 0W? Because someone told you?
Let's look at the 15W-50 and 0W-40 I would start with. Based on Daves use of his car, bearing in mind it's not pushed hard operating temps are about 100C at MAX, and most of the time below. It often does short trips too. Let's compare those two choices:
PRO R 15W-50
18.2 mm^2/s @ 100C
130 mm^2/s @ 40C
Mobil 1 15W-50
17.4 mm^2/s @ 100C
125 mm^2/s @ 40C
Compare that to my choice Mobil 1 0W-40 fully synth:
14 mm^2/s @ 100C
78.3 mm^2 @ 40C
From that it's clear that the Mobil 1 0W-40 offers far better protection at lower temperatures. As temperature drops both can only get worse and personally I'd rather it got worse from 78.3 than 130. Even at 100C there will be (although marginal) better flow with Mobil 1 0W-40 up to probably 110C looking at this. Beyond these temperatures a 10W-50 might be advisable if this is frequent.
So based on the facts:
1 Car does short trips
2 Car does a lot of cold starts
3 Car isn't thrashed and operating temps are around 100C at max or lower
What would your justification be for selecting 15W-50? I am genuinely interested to know.
Craig
Addition.... oh and I am gobsmacked that you'd put a 10W oil in this car in winter!? What is the logic here?
02 September 2010, 05:43 PM
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Craig,
Can you expand on importance of flow? At 100ºC a 0W-20 oil (very thin) would surely have higher flow than a 0W-40, so why not use this? And how does the film strength of the thinner oil albeit with greater flow, compare to a thicker oil? And what is the result on bearing protection? And how might such a choice be influence by mileage and current engine wear?
Can you expand on importance of flow? At 100ºC a 0W-20 oil (very thin) would surely have higher flow than a 0W-40, so why not use this? And how does the film strength of the thinner oil albeit with greater flow, compare to a thicker oil? And what is the result on bearing protection? And how might such a choice be influence by mileage and current engine wear?
02 September 2010, 06:23 PM
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Now you're thinking! Good questions, why not use the thinnest oil money can buy? Well this is partly true, think about it this way. I will try to answer this to the best of my knowledge now and look at those other questions later or I'll be here all night typing.
Let's take this, and please bear in mind that all this is detailed within the article to which I refer.
We'll start with a 30 weight oil which looks like this (roughly):
3 mm^2/s @ 150C
10 mm^2/s @ 100C
100 mm^2/s @ 40C
250 mm^2/s @ 0C
Engines are generally designed to run with oil at a thickness of mm^2/s at about 10 when at normal operating temperature. That's why oils you get are approaching that thickness at operating temperatures. This is irrespective of your ambient conditions, be it the Arctic or Death Valley. Your cars cooling system should maintain a stable temperature and the oil thickness should be around 10 at all times. If it's not there could be a problem with the cooling system. Anyway back to topic.
If the thickness was 10 all the time, regardless or temperature you'd never have to warm your engine up. You could give it a bootfull from the get go. Unfortunately no one has invented such an oil and as a consequence we have to make do with what we've got.
Back to pressure and thickness, the general gold standard is that for every 1,000 rpm, the PSI should be +10. So 1000 = 10 PSI, 3000 = 30 PSI and so forth. This is ideally what you want to achieve but most people unfortunately don't have oil pressure guages (I imagine a lot will pipe up on this forum saying they do ). You don't want anymore or any less really, you need some pressure to move the oil but only enough. Too much pressure is not good, it can only result in the restriction of flow. Too little pressure and the pressure you are providing isn't providing enough flow of oil through the engine. Flow is your lubrication, the better the flow, the better the protection generally.
Pressure at a given viscosity is what determines the flow. If your pressure is too low at a given RPM (i.e. not meeting you 10PSI for every 1000rpm) because the fluid is very thin (this will only be at OPERATING temp btw all oils are too thick at cold start) then you are not achieving the flow you require for lubrication. Most manuals stipulate a target pressure for given RPM, this is your aim.
The thicker the oil the more resistance it has to flow, so when cold your 15W is going to reach high PSI for relatviely low rpm. Thus at high rpm starving the engine of oil. In fact it probably does this at relatively low rpm! Most oil pumps have a cut off point (PSI cut off valve), where a valve is released when the pressure hits the maximum value and the pump bypasses. This is not good, your flow will not increase from this point forward with rpm at all so you will not acheive the flow rate required to provide protection.
It is most likely that a 0W-20 oil will actually provide you a lower pressure at a given RPM than required to provide the flow required for lubrication at operating temperature. For example at 4000rpm the pressure may be 25PSI, which is too low and flow is less. It is a happy medium. If you have a pressure gauge it's a good thing to look at, what is your oil pressure at 6000rpm? Is it around or close to 60PSI (or whatever pressure Subaru specifies). If it's too high, try a thinner oil at operating temperature, if it's too low maybe you require something thicker at operating temperature.
I didn't go into this in a lot of detail and I apologise if any of it appears vague, as I said there is a detailed article on this subject. It's 40 pages long and goes into minute details that I wouldn't in a post on here.
I am genuinely trying to help people here! I don't want to appear difficult but I just get frustrated about this subject. If you need further explaination I will try to help
Hope that helps.
Craig
Let's take this, and please bear in mind that all this is detailed within the article to which I refer.
We'll start with a 30 weight oil which looks like this (roughly):
3 mm^2/s @ 150C
10 mm^2/s @ 100C
100 mm^2/s @ 40C
250 mm^2/s @ 0C
Engines are generally designed to run with oil at a thickness of mm^2/s at about 10 when at normal operating temperature. That's why oils you get are approaching that thickness at operating temperatures. This is irrespective of your ambient conditions, be it the Arctic or Death Valley. Your cars cooling system should maintain a stable temperature and the oil thickness should be around 10 at all times. If it's not there could be a problem with the cooling system. Anyway back to topic.
If the thickness was 10 all the time, regardless or temperature you'd never have to warm your engine up. You could give it a bootfull from the get go. Unfortunately no one has invented such an oil and as a consequence we have to make do with what we've got.
Back to pressure and thickness, the general gold standard is that for every 1,000 rpm, the PSI should be +10. So 1000 = 10 PSI, 3000 = 30 PSI and so forth. This is ideally what you want to achieve but most people unfortunately don't have oil pressure guages (I imagine a lot will pipe up on this forum saying they do
). You don't want anymore or any less really, you need some pressure to move the oil but only enough. Too much pressure is not good, it can only result in the restriction of flow. Too little pressure and the pressure you are providing isn't providing enough flow of oil through the engine. Flow is your lubrication, the better the flow, the better the protection generally.Pressure at a given viscosity is what determines the flow. If your pressure is too low at a given RPM (i.e. not meeting you 10PSI for every 1000rpm) because the fluid is very thin (this will only be at OPERATING temp btw all oils are too thick at cold start) then you are not achieving the flow you require for lubrication. Most manuals stipulate a target pressure for given RPM, this is your aim.
The thicker the oil the more resistance it has to flow, so when cold your 15W is going to reach high PSI for relatviely low rpm. Thus at high rpm starving the engine of oil. In fact it probably does this at relatively low rpm! Most oil pumps have a cut off point (PSI cut off valve), where a valve is released when the pressure hits the maximum value and the pump bypasses. This is not good, your flow will not increase from this point forward with rpm at all so you will not acheive the flow rate required to provide protection.
It is most likely that a 0W-20 oil will actually provide you a lower pressure at a given RPM than required to provide the flow required for lubrication at operating temperature. For example at 4000rpm the pressure may be 25PSI, which is too low and flow is less. It is a happy medium. If you have a pressure gauge it's a good thing to look at, what is your oil pressure at 6000rpm? Is it around or close to 60PSI (or whatever pressure Subaru specifies). If it's too high, try a thinner oil at operating temperature, if it's too low maybe you require something thicker at operating temperature.
I didn't go into this in a lot of detail and I apologise if any of it appears vague, as I said there is a detailed article on this subject. It's 40 pages long and goes into minute details that I wouldn't in a post on here.
I am genuinely trying to help people here! I don't want to appear difficult but I just get frustrated about this subject. If you need further explaination I will try to help
Hope that helps.
Craig
Last edited by captain_anonymous_2003; 02 September 2010 at 06:25 PM.
02 September 2010, 06:27 PM
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Tony,
I am sorry but again you've said that an oil choice is perfectly fine with no knowledge of the operating conditions of the engine whatsoever, how can you make an accurate recommendation without that information? You can't, it's as simple as that. I am not saying his car will explode and it's the worst oil possible, I am saying based on his car operating conditions this choice is poor.
I am sorry but again you've said that an oil choice is perfectly fine with no knowledge of the operating conditions of the engine whatsoever, how can you make an accurate recommendation without that information? You can't, it's as simple as that. I am not saying his car will explode and it's the worst oil possible, I am saying based on his car operating conditions this choice is poor.
Addition.... oh and I am gobsmacked that you'd put a 10W oil in this car in winter!? What is the logic here?
HTH
Tony
02 September 2010, 06:33 PM
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Tony,
Again I think you've missed my point. And you've done the classic thing that most do when it comes to this.. "this is what the subaru people say.. they must be right and you're wrong.. ".... They have recommended an oil based on their requirements for the engines they produce ok.. which is pretty much..
1 - NO BLOW UPS and warranty repairs.
So.. if they were to say put in an oil that was acceptable for 90% of drivers but 10% would destroy their cars within 16months of ownership it's not cost effective. Much better to choose an oil that does the job for all eventualities (and I use this term loosely, because we've seen how a 15W isn't great for cold start short trips, sure it'll work, but not very well) for at least 3 years.. that makes life easier for them.. Oil choice is subjective and based on how you use you car.. and very little else. There is no one size fits all. Like I've shown you, how a 15W-50 for one driver is rubbish but for a racer is great, however a 0W-30 would be the other way around. This is the same reason I imagine BMW chose 10W-60, and why after warranty had expired they said actually 5W-30 is ok.
Again I think you've missed my point. And you've done the classic thing that most do when it comes to this.. "this is what the subaru people say.. they must be right and you're wrong.. ".... They have recommended an oil based on their requirements for the engines they produce ok.. which is pretty much..
1 - NO BLOW UPS and warranty repairs.
So.. if they were to say put in an oil that was acceptable for 90% of drivers but 10% would destroy their cars within 16months of ownership it's not cost effective. Much better to choose an oil that does the job for all eventualities (and I use this term loosely, because we've seen how a 15W isn't great for cold start short trips, sure it'll work, but not very well) for at least 3 years.. that makes life easier for them.. Oil choice is subjective and based on how you use you car.. and very little else. There is no one size fits all. Like I've shown you, how a 15W-50 for one driver is rubbish but for a racer is great, however a 0W-30 would be the other way around. This is the same reason I imagine BMW chose 10W-60, and why after warranty had expired they said actually 5W-30 is ok.
Last edited by captain_anonymous_2003; 02 September 2010 at 06:36 PM.
02 September 2010, 07:10 PM
#22
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Interesting thread, i have a lot of time for both Tony and Paul Zen) not that i would admit it
I know nothing of yourself Captain but am interested in what you have to say
I know nothing of yourself Captain but am interested in what you have to say
02 September 2010, 07:14 PM
#23
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So Craig,
If we were to run a 0W-20 with a higher flow oil pump, such that we could maintain 10psi per 1000rpm of engine speed, surely that will give better overall protection over a wider range of temperatures?
If we were to run a 0W-20 with a higher flow oil pump, such that we could maintain 10psi per 1000rpm of engine speed, surely that will give better overall protection over a wider range of temperatures?
02 September 2010, 07:28 PM
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But we are losing sight of the discussion and talking extremes. A 0W-20 is unsuitable because pressure can't be maintained to deliver the flow in your engine. A 15W-50 is too thick for a lot of applications and provides poor cold start protection. A 0W-40 is the best of both worlds without the detriment of either, it requires no modifications and the difference in thickness is getting smalled. This is assuming normal driving conditions.
0W-20
50 mm^2/s @ 40C
0W-40
78 mm^2/s @ 40C
Those are rough estimates, think of the differences with a 15W-50.
15W-50
130 mm^2/s @ 40C
Do you see what I am getting at? Incidentally a 0W-20 is about 8 mm^2/s @ 40C. You will also want to consider the longevity of the 0W-20, how many top us, etc etc. I would not recommend that to anyone without looking at their car in detail.
think I will stick with my 5w oil thanks or my 15w oil in summer
02 September 2010, 08:33 PM
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How can the ability of 0w-20 to survive hard driving be limited? Provided we keep the pressure up, and the flow mega, your posts suggest that any oil no matter how thin will protect the engine bearings if pressure is maintained.
Would you not agree that the two bearing surfaces we are trying to keep apart don't really give a stuff about the oil pressure at the bearing journal? And it's the oil's film strength that gives the protection, and on a 0W-20 oil at 100ºC that is somewhat lacking. It doesn't matter how fast you replenish the oil that is lost from the bearing because with enough force the rod bearing will come into contact with the crank journal and no amount of conventional oil pressure will stop this from happening. When the forces involved are in the order of 15000N, it is quit reasonable to imagine that the oil film strength can be sufficiently low that the flow of oil will just be shut off to the loaded areas of the bearing as the two sides make contact and just displace the oil that was there.
I would be very cautious about employing 0W-40 or thinner oils in a high mileage subaru engine running 50% more than standard power.
Would you not agree that the two bearing surfaces we are trying to keep apart don't really give a stuff about the oil pressure at the bearing journal? And it's the oil's film strength that gives the protection, and on a 0W-20 oil at 100ºC that is somewhat lacking. It doesn't matter how fast you replenish the oil that is lost from the bearing because with enough force the rod bearing will come into contact with the crank journal and no amount of conventional oil pressure will stop this from happening. When the forces involved are in the order of 15000N, it is quit reasonable to imagine that the oil film strength can be sufficiently low that the flow of oil will just be shut off to the loaded areas of the bearing as the two sides make contact and just displace the oil that was there.
I would be very cautious about employing 0W-40 or thinner oils in a high mileage subaru engine running 50% more than standard power.
In effect yes, you would get a better protection at low temperature cold starts (although even a 0W-20 is still too thick for cold starts) but the same protection at 100C. However the ability of the 0W-20 to survive hard driving would be limited I expect and oil consumption would probably be high depending on the spec of the oil. I imagine the modification required to the pump would need to be very substantial and not warrant the gain you'll get.
But we are losing sight of the discussion and talking extremes. A 0W-20 is unsuitable because pressure can't be maintained to deliver the flow in your engine. A 15W-50 is too thick for a lot of applications and provides poor cold start protection. A 0W-40 is the best of both worlds without the detriment of either, it requires no modifications and the difference in thickness is getting smalled. This is assuming normal driving conditions.
0W-20
50 mm^2/s @ 40C
0W-40
78 mm^2/s @ 40C
Those are rough estimates, think of the differences with a 15W-50.
15W-50
130 mm^2/s @ 40C
Do you see what I am getting at? Incidentally a 0W-20 is about 8 mm^2/s @ 40C. You will also want to consider the longevity of the 0W-20, how many top us, etc etc. I would not recommend that to anyone without looking at their car in detail.
But we are losing sight of the discussion and talking extremes. A 0W-20 is unsuitable because pressure can't be maintained to deliver the flow in your engine. A 15W-50 is too thick for a lot of applications and provides poor cold start protection. A 0W-40 is the best of both worlds without the detriment of either, it requires no modifications and the difference in thickness is getting smalled. This is assuming normal driving conditions.
0W-20
50 mm^2/s @ 40C
0W-40
78 mm^2/s @ 40C
Those are rough estimates, think of the differences with a 15W-50.
15W-50
130 mm^2/s @ 40C
Do you see what I am getting at? Incidentally a 0W-20 is about 8 mm^2/s @ 40C. You will also want to consider the longevity of the 0W-20, how many top us, etc etc. I would not recommend that to anyone without looking at their car in detail.
02 September 2010, 11:13 PM
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This is a silly thing to say, and the fact that you smile and laugh after just shows the ignorance on this subject. Every oil you buy is too thick at startup. Simple as that, if you can find one that's not from cold and make it work in the internal combustion engine environment, you'll be a billionaire.. Castrol haven't done it, Mobil, Shell... but perhaps you have?
Last edited by captain_anonymous_2003; 02 September 2010 at 11:14 PM.
02 September 2010, 11:42 PM
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I would say if you can use 0W-20 in a car, the oil pressure, temperatures and so forth are favourable then why not use it? I imagine in a higher mileage car you won't be in that position. But don't assume because your car is high mileage that you need to bump up the thickness. You're basing your oil choice on "what ifs", base them on facts. What is the engine oil pressure doing with RPM? What are the operating temperatures? How many cold starts are you doing? How often do you change? Find this information and make an informed choice.
You are all missing my main point, which is how on earth can you recommend an oil without knowing how the car is operated!? I go running every day for 7 miles and I like these trainers so everyone else should use them regardless of what they are doing. It's nuts isn't it? So why is engine oil vastly different?
Yes the thinner the liquid the better, water in fact would be a brilliant lubricant if it could be supplied sufficiently, and of course could survive the operating environment in the engine, and of course not react with any engine parts, and of course... etc.. etc.... In fact it has a higher specific heat than oil. Alas it does react with metals and so forth, making it terrible choice for engines, however other applications it might be perfectly acceptable.
I refer to:
"I truly believe that oil is much better being too thin than too thick. Over the years we have been going to thinner and thinner oils despite hotter engines with turbos and the like. The tendency is that people figure they need a 40 weight oils but then use a 50 instead. Better thinking is that if you think you need a 40, use a 30 weight oil instead. I firmly believe this based on all I know about oils.
As it turns out synthetic oils do cling to parts better as they have higher film strength than mineral oils. Synthetics are thinner overall. They have greater slipperiness. Yet they stick better to engine parts. Again, this concept is the opposite of normal thinking."
Addtionally, lubrication is FLOW:
"Furthermore pressure does not equal lubrication. Let us look at a single closed “lifetime lubricated” bearing. We could hook up a system to pressurise the bearing. This can actually be done. We could have the oil at ambient pressure. We could then double, triple, quadruple the pressure of the oil. The oil is non-compressible. Regardless of the pressure we would have the exact same lubrication, that of the ambient pressure lubrication.
The physics of lubrication as I said earlier show a 1:1 relationship of flow to separation pressure. Lubrication itself is pressure independent. I will not go into the mathematical equations for this."
Rather than me just continuously pump this stuff out, you should take the time to read it yourself. It's very interesting and useful. It completely changed my approach to engine oil choices. Ultimately, if you really want to know how well your oil is doing, get a UOA done, have you done this? What were the results? Did they suggest the oil was doing it's job and that wear was minimised or not?
You are all missing my main point, which is how on earth can you recommend an oil without knowing how the car is operated!? I go running every day for 7 miles and I like these trainers so everyone else should use them regardless of what they are doing. It's nuts isn't it? So why is engine oil vastly different?
Yes the thinner the liquid the better, water in fact would be a brilliant lubricant if it could be supplied sufficiently, and of course could survive the operating environment in the engine, and of course not react with any engine parts, and of course... etc.. etc.... In fact it has a higher specific heat than oil. Alas it does react with metals and so forth, making it terrible choice for engines, however other applications it might be perfectly acceptable.
I refer to:
"I truly believe that oil is much better being too thin than too thick. Over the years we have been going to thinner and thinner oils despite hotter engines with turbos and the like. The tendency is that people figure they need a 40 weight oils but then use a 50 instead. Better thinking is that if you think you need a 40, use a 30 weight oil instead. I firmly believe this based on all I know about oils.
As it turns out synthetic oils do cling to parts better as they have higher film strength than mineral oils. Synthetics are thinner overall. They have greater slipperiness. Yet they stick better to engine parts. Again, this concept is the opposite of normal thinking."
Addtionally, lubrication is FLOW:
"Furthermore pressure does not equal lubrication. Let us look at a single closed “lifetime lubricated” bearing. We could hook up a system to pressurise the bearing. This can actually be done. We could have the oil at ambient pressure. We could then double, triple, quadruple the pressure of the oil. The oil is non-compressible. Regardless of the pressure we would have the exact same lubrication, that of the ambient pressure lubrication.
The physics of lubrication as I said earlier show a 1:1 relationship of flow to separation pressure. Lubrication itself is pressure independent. I will not go into the mathematical equations for this."
Rather than me just continuously pump this stuff out, you should take the time to read it yourself. It's very interesting and useful. It completely changed my approach to engine oil choices. Ultimately, if you really want to know how well your oil is doing, get a UOA done, have you done this? What were the results? Did they suggest the oil was doing it's job and that wear was minimised or not?
02 September 2010, 11:45 PM
#30
Double edge sword then...... 
Too thin an oil will cause microwelds as surfaces touch and it's low mass-specific heat capacity will not carry away heat from combustion in the cylinders.......
Back to a compromised oil like Silkolene Pro-R or as it is now called Fuchs Titan Pro-R 15w50. ..........which I use in my car
Shaun
Too thin an oil will cause microwelds as surfaces touch and it's low mass-specific heat capacity will not carry away heat from combustion in the cylinders.......
Back to a compromised oil like Silkolene Pro-R or as it is now called Fuchs Titan Pro-R 15w50. ..........which I use in my car
Shaun