TonyBurns

iTrader: (3)

Actually you have no idea, have you actually read what he said or did you just pick out the parts you wanted to?
He has lots of good arguments, yes this is great for an engine that to build and then buy would cost inexcess of the top of the range factory Subaru Impreza STI, built to far tigher tolerences, and then he goes and does this.....

Carry on Craig, more than interested to see what you think?

Tony

TonyBurns

iTrader: (3)

He even agree's that cars with more miles on them require a thicker hot oil, he said his ferrari may require a 30 then a 40 and even a 50 weight, wow, and guess what? He doesnt run his ford on a 0w oil damn, mega wear and tear eh?!

Tony

captain_anonymous_2003

AGAIN, no argument against 0Ws!!!!! I am picking parts out of this that suit me? Why didn't you include this Tony, in the same section!

"Remember, the only difference between a 0W-40 and a 10W-40 is that the 0W-40 thickens less after you turn off your engine. It is still too thick in the morning at startup but not as thick as the 10W-40. Yet, they are still too thick to use until they both warm up to operating temperature at which point they have the save viscosity, around 13 to 14. Remember that the 0W-30, 10W-30 and straight 30 weight oils all have a viscosity of around 10 at normal engine operating temperatures.

There is one more thing. A 20 weight oil is not half as thick as a 40 weight oil. The real scale is more like the oils having an absolute thickness of 108 and 114. Now it can be seen that the 40 weight oil is only around 10 percent thicker than the 20 weight oil. The difference is not that much at operation but at startup the difference is significant. Pressure / flow dynamics go along with this 10 percent figure. A 30 weight oil should be thought of as having an absolute viscosity of 110 and a 50 weight oil has an absolute viscosity of 120. I am talking about operating temperatures.

I thought everyone knew that 90 percent of engine wear occurs during the startup period because oil is just too thick. Some think it is good to have a thicker oil for startup since the parts shrink when cold and would otherwise “rattle.” Sure, your piston diameter will shrink on cooling but so will the diameter of your bore. The net result is about the same clearance hot and cold. This is not true for your valves. They lengthen when extremely hot. In the Murcielago they use shims instead of self adjusting valve tappets. You need to put a millimeter of clearance there so that after expansion the valve will not be held partly open when it is supposed to be closed.

If it were true that thicker oils were needed at startup then the manufacturers would not be requesting oils that thicken less on cooling. They would just specify that one should use a straight 30 or 40 weight oil. Instead, over time, they are specifying thinner and thinner oils.

The manufacturers know what parts shrink or expand and the clearance changes that result. You do not have to worry about this. If it was that easy to design engines we would all be making them.

I would like to go back to the worry that oil falls off the parts when a car is stored or sees long periods of inactivity. For the first oil change in my 575 Maranello I drained the Shell and put in 0W-30 Mobil 1. This was at 775 miles on the odometer. I drove the car home from work, put it on the lift and drained the transaxle and engine oils. I also opened and drained the oil cooler and took off every line that is in the oil system. I wanted to get every speck of the Shell oil out of there. For optimal results you are not supposed to mix synthetic oils of different brands.

The system takes 12 quarts with a “normal” oil change but took 15 quarts for this change. It all took about an hour. I then started the engine to check for leaks. The multitude of mechanical engine noises that followed nearly broke my eardrums for about 10 long seconds. Then it was suddenly very quiet. You could hear a pin drop. There was certainly the most possible amount of surface oil on all the internal parts as the engine was only off for an hour. But it was not until the oil circuit primed, filled then sent flow into all the parts that any lubrication was occurring. Hence all oil filters that are manufacturer certified have back flow limiters to keep the oil filter full even with the engine off."

Tony obviously only read part of this.. you know what oil he was putting in his car people? Yep... a 0W

"When I took delivery of my 575 Maranello I drove for 500 miles then changed the oil to 0W-30 Mobil 1. There were no changes in operating pressure or temperature. Starting the engine seemed faster though. I called up FNA and was told that all new Ferrari cars are delivered with 5W-30 Shell Helix Ultra. That is when I decided to try the 0W-20 Mobil 1. I could even go to a 10 weight oil as my pressures are still excessive while driving around town. I do not drive on the track."

Why are people still listening to you? In fact ironically what you've pointed to here supports what I am saying!

TonyBurns

iTrader: (3)

I have read what he has put, he runs his Ford Exploration on a 5w oil, ever thought why he doesnt run it on a 0w one?
Have you ever owned a subaru also? just a run of the mill question.....

Probably because they dont want to damage their engines, but you dont seem to understand that, if you have a clue, then go read the 2nd quoted part I put in post 121, then go and have a good think about it.

Tony

captain_anonymous_2003

I included the second para you quoted Tony, it had no context on its own so supported neither of us, however with the context it actually supports what I am saying.. He openly says.. he went from a 5W-30 Shell, to 0W-30.. he's thinking of a 0W-20.. and could even go to a 0W-10.. you must be horrified.. But hey what does he know? I mean he's just an expert in fluid dynamics but hey..

ZEN Performance

Tony,

10 seconds of that on a Subaru would be the end!

TonyBurns

iTrader: (3)

You still dont get it do you?
He is demonstrating on a Ferrari engine, for the cost of that engine you can buy 2 ford focus 1.6's, a 2.5ltr STI 330s, 1 BMW 520d, getting the point?

All the above are mass produced cars, that ferrari is probably hand built, has all the pistons fine honed to within .001 rather than a variance of .004 on your normal car, he can run oils like that, a 20 year old+ engine design cant, help yourself, most of what he put I knew anyway, you dont also understand that in his 10 seconds of "madness", he probably caused 100k miles worth of wear on that engine, no 0w oil will repair that.

Tony

TonyBurns

iTrader: (3)

Yup!

captain_anonymous_2003

That's utter rubbish Tony.. At no point did I suggest using a 0W-10 in a Subaru. My disagreement with you is the use of 0W-40.. or 0W-50.. in a Subaru.. which I believe is perfectly acceptable.. You still.. STILL have got nothing to go on that says that's unsuitable.. All the evidence... physics.. knowledge about Synthetics.. and so on fly in the face of your dogmatic view that 0W's are harmful.. They simply aren't.. If I had a scooby.. I'd use 0W-40.. 5W-40... 5W-50.. or 0W-50.. depending on how strapped for cash I was... People use 10W's because of NOISE, no other reason, oilman said the same.

You knew it all did you? And yet you still think 0W's are bad.. that's irony right there..

captain_anonymous_2003

10 seconds on a 0W-20? I'd be fine actually, but there are other factors that would come into it using an oil like that, that would simply make it totally impractical. I am not sure how well it would cope with any lengthy service interval. I would have to do an analysis after a very short time. This why 0W-20's aren't in common use, because they don't perform well for cars that are used as daily drivers.. much better with a 30 or 40. 0W-20 or 0W-10 is a no compromise for a garage queen, that rarely goes anywhere, but for every day cars would be impractical. Oh and of course there is a the bag of spanners din it would make..

If you used it with any extensive service interval and pushed the car regularly, I imagine that results would be far from favourable. So no.. I wouldn't subscribe to a 0W-20 being suitable.. I think you might be ok on a 30.. but I think 40 is the happy medium for most drivers. But, without analysis and understanding driving style it's very hard to recommend. I will leave that to oilman (Tim).

TonyBurns

iTrader: (3)

Do you understand what NOISE is?
Or have we lost you?

TonyBurns

iTrader: (3)

captain_anonymous_2003

Please if you're going to quote me, quote everything I say.. Or you take what I say completely out of context to make me sound stupid which I am not. So include my entire post or don't at all thank you.

I await your reasoning why a 0W is bad.. still.. it's been a long time now and you still are unable to come up with anything to support your view.

gallois

i don't think the foibles of bearing oil starvation on the scoob engine after an oil change are in question here, this would happen using any grade, it is the reason why a 0w oil is not suitable but a 10w or 15w is ok, why is 0w not suitable? There is no logical explaination for this.

TonyBurns

iTrader: (3)

Still you have not replied if you know what noise is associated with (and im working btw, so as im busy im just fitting this in between)

TonyBurns

iTrader: (3)

Engine design and lubrication factors are probaly the biggest issue, just remember this isnt a ferrari engine, its a main stream production unit.

ZEN Performance

There is nothing fundamentally wrong with a 0w oil, and it's nice to have an oil that's thin when the engine is cold. However trying to get an 0w oil that's stable at higher temperatures can be an issue. A Subaru engine is very fussy when it comes to oil and bearings, as the bearings are narrow and there are a few issues that can be a serious problem if everything bad happens at once.

I would certainly advocate the use of the thinnest oil that is appropriate, but for a lot of cars owned by people on here 0W-30 is probably not a good idea.

gallois

thank you zen, a logical explaination at last.

It seems, for the scoob, that one of the first mods should be an accurate oil temp & oil pressure gauge.

the answer then is surely:-

If you running oil at 100deg regularly, then 40 weight is good (0w40 might be unstable at higher temps due to VI improvers?, so 5w40 or 10w40 is better for stable high temp performance on a car that is around 100deg more often than not)

if you regularly exceed 100deg i.e. track driven, or always driven hard, then a 50 or 60 weight (depending on temp) is preferable, but why not 5w50 instead of 15w50, is this also due to the oils stability at higher temps, is a 15w50 more stable than a 5w50?

Maz

iTrader: (34)

Which is basically what captain anonymous is saying. Choose an oil based on how the car is driven. He (captain anonymous) couldn't have made things more simple unless he'd drawn pictures.

captain_anonymous_2003

I agree with what is said here mostly, there is nothing fundamentally wrong with the use of a 0W oil in this car. It's a great idea to have an oil that's as thin as possible at low temperature to reduce wear and ensure the highest flow possible early on. A Subaru engine is certainly no more fussy than my M5 engine, there isn't anything particularly special about this engine I am sorry to say. My M5 engine runs perfectly happily with 0W-40 bearing in mind it's operating conditions suit this weight.

I would agree that a 0W-30 is not a good idea but for different reasons. I imagine the consumption may be higher and this would make it impractical to use for a daily driver. Same with lower weights like 20's or 10's. Their ability to protect the engine isn't a problem but their shear characteristics and consumption rates would make servicing expensive (far more oil changes) and for the gain you'd get it most likely wouldn't be cost effective. This is why I asked oilman about 5W-30 for my car. I would go 5W-30 because it's more likely to withstand shear (than a 0W-30) but I might compromise slightly my cold start protection (although I'd have to look at the thicknesses at 40C in more detail for both). As oilman mentioned he's seen high consumption with this viscosity, as a result most tend to choose thicker as it is more cost effective and they're not forever dropping the oil and replacing it (as well as topping up!). I think my consumption right now is acceptable if it were to increase dramatically I might spend a lot more on oil and it wouldn't be worth it to me if the 0W-40 is doing the job for now.

As for noise, it's just that the thicker weight oil dampens the vibration within the engine that causes that noise more effectively. However this is not necessarily directly linked to the protection offered (neither is consumption btw). Synthetics stick very well to moving parts like bearings and provide a perfectly adequate barrier, we've already explained why (esters). The noise in this case is personal preference and nothing to do with mechanical wear of the engine when we are comparing a 0W, 5W, or 10W. It's personal preference! Oilman even explained this in his post earlier. When he rightly commented that I wasn't taking into account personal preference, a perfectly valid point as to which you might choose a 5W or 10W. But at no point did he contradict that a 0W provides better cold start protection that both a 5W and 10W.

When at temperature there will be relatively little difference in terms of noise as most oils are in the same viscosity range, and certainly little difference in terms of wear. The advantage of the 0W is that at low temperature flow rates are higher and as we all know flow is directly linked to lubrication, this can't be a bad thing for an engine.

Still there is no reason why you shouldn't use a 0W. I don't know how much a 0W-50 is, I bet it's not cheap but that'd be a great choice for someone who drives hard all the time and wants better low temp protection too. Yet no one has advocated or suggested this weight?

I think you'd struggle to justify the use of a 15W for most people on this forum.

captain_anonymous_2003

I would agree with most that is said here too. I would say that a 15W-50 would be more stable at high temps for long service intervals than a 5W-50 or 0W-50. But those oils aren't going to be far off to be honest. But they come at a price! And that's why you see, it's hard to make oils that offer good cold start protection and also good constant high performance high temperature protection. This is why they're generally more expensive. I would still go more for a 5W-40 or 0W-40 than 10W-40. I would perhaps keep service intervals lower with a lower weight though and get a UOA to see how it's doing in terms of wear and shear between cycles.

Sabas

iTrader: (22)

So, a thinner oil might need changing more frequently then a thicker oil?

Or does it depend on consumption?

Or have I missed the point? Which is probably the case!

ZEN Performance

A subaru engine IS very much more fussy than just about every other performance engine when it comes to oil quality and grade. What you will get away with just fine on with an 4g63, RB26 or YB engine will routinely kill a Subaru engine.

Turbotits

iTrader: (2)

wow turned into some thread,

The techical stuff is a little beyond me, But i can say ive used a 0/40 and found it too noisey on start up(piston slap). To my mind if i can aduible hear metal on metal rattle then theres either no oil there between the sufaces or its two thin, I switched to 5/40 and the engine became much quieter but still had some slight rattle so i switched to 10/50 some months ago and havent had any rattle or noise at start up at all. I do a mix of town,motorway and some track stuff and it seems to suit all these applications. oh and the cars done 97k

oilman

iTrader: (9)

Sorry double post

oilman

iTrader: (9)

A very long time ago (more than 5 years) we posted this by an oil "expert", perhaps worth a re-read for those that have lost the plot on the teccie stuff......it was written for pre 2000 scoobs, we all know that the post 2000 ones require 5w-30's and 5w-40's in stock configuration.

Lubricating the Subaru.

Basically

Basically, to use that irritating in-word, engine lubrication is simple, and consequently boring. So I intend to treat the subject “complicatedly”, which may not be an in-word, but makes life far more interesting!

So, to take a quick look at the simple picture; the oil keeps moving parts apart, reducing friction and carrying away heat. Where there is metal-to-metal contact there are chemicals in the oil to reduce damage. Because the internal combustion process is always less than perfect, some soot is produced and this must be washed off the pistons and rings by the oil, so it has a cleaning or detergent function as well.

The trouble is, all this is just as true for Henry Ford’s original Model T engine as it is for the Subaru or any other high output motor. So where is the difference? The Model T, with 10bhp/litre at 2,000rpm and a single underhead camshaft, was filled with a thick, greenish liquid from somewhere near the bottom of the distillation colums on the Pennsylvania oilfields. It did a vague tour of the internals by guesswork (there was no oil pump) at a temperature around 50 degC, and lasted for 1,000 miles. On the plus side, some of the impurities acted as anti-wear and detergent chemicals. They didn’t work very well, but it was better than nothing. The engine wore out in around 20,000 miles, but even ordinary people, not just amateur rally drivers, were happy to put up with this.

The difference begins with the first turn of the key. The modern high-pressure pump would cavitate on the old heavy monogrades, starving the bearings for a vital couple of seconds, even in warm weather. Likewise, cam lobes would suffer as the sluggish oil found its way along narrow oil ways to the valve gear. The turbo bearing (if fitted as the handbooks say) already spinning fast, would also starve, and when it got going, how long would it be before the heat soak-back fried the primitive oil into a lump of carbon? (This was the problem with “modern” oils only 15 years ago).

So, a good oil must be quite low in viscosity even in the cold, so that it gets around the engine in a fraction of a second on start-up. On the other hand, it must protect engine components (piston rings for example) at temperatures up to 300 degC without evaporating or carbonising, and maintain oil pressure.

Unmodified thin oils simply can’t manage this balancing act. The answer is to use a mixture of thin oil and temperature-sensitive polymer, so as the thin oil gets even thinner with increasing temperatures as the engine warms up, the polymer expands and fights back, keeping the viscosity at a reasonable level to hold oil pressure and film thickness on the bearings. This is called a multigrade.

But, this is all too basic! What I have just written was and is relevant to a 1958 Morris Minor.

The questions that Subaru owners need to ask are: “Will this thin oil evaporate and be drawn into the intake manifold (via the closed circuit crankcase ventilation), leading to combustion chamber deposits and de-activated catalysts?” and “Will the polymer shear down at high engine revolutions and high temperatures, causing low oil pressure and component wear?” and “Will it carbonise on the turbo bearing?” These are 21st century questions which cannot be answered by a basic 1990’s approach.

BUT! Before we head into more complications, some figures………

The SAE Business (American Society of Automotive Engineers)

Viscosity is the force required to shear the oil at a certain speed and temperature. Oils work because they have viscosity; the drag of a rotating part pulls oil from a low-pressure area into a high pressure area and “floats” the surfaces apart. This is called “hydrodynamic lubrication”, and crank bearings depend on it. In fact a plain bearing running properly shows literally no metal-to-metal contact. Experimental set-ups have shown that electrical current will not flow from a crank main bearing to the shells. Also, the energy loss due to friction (the co-efficient of friction) is incredibly low, around 0.001. So for every kilogram pulling one way, friction fights back with one gram. This is very much better than any “dry” situation. For example, the much over-rated plastic PTFE has a co-efficient of friction on steel of 0.1, 100 times worse than oil.

Oil viscosities are accurately measured in units called “Centistokes” at exactly 100 degC. These fall into five high temperature SAE catagories:-

SAE No. 20 30 40 50 60
Viscosity Range 5.6 - <9.3 9.3 - <12.5 12.5 - <16.3 16.3 - <21.9 21.9 - <26

A decent quality oil usually has a viscosity that falls in the middle of the spec, so a SAE 40 will be about 14 Centistoke units, but SAE ratings are quite wide, so it’s possible for one 40 oil to be noticeably thicker or thinner than another.

When the polymer modified multigrades appeared, a low temperature range of tests were brought in, called “W” for winter (it doesn’t mean weight). These simulate cold start at different non-ferrous monkey endangering temperatures from –15 degC for the 20w test to a desperate –35 degC for 0w. So, for example, an SAE 5w-40 oil is one that has a viscosity of less than 6600 units at –30 degC, and a viscosity of about 14 units at 100 degC.

Now, those of you who have been paying attention will say “Just a minute! I thought you said these multigrade polymers stopped the oil thinning down, but 6600 to 14 looks like a lot of thinning to me!”. Good point, but the oil does flow enough to allow a marginal start at –30 degC, and 14 is plenty of viscosity when the engine is running normally. (A lot more could damage the engine. Nobody uses the 24 viscosity SAE 60 oils any more.) The vital point is, a monograde 40 would be just like candle wax at –30 degC, and not much better at –10 degC. It would even give the starter motor a fairly difficult time at 0 degC. (At 0 degC, a 5w-40 has a viscosity of 800 but the monograde 40 is up at 3200!)

Another basic point about wide ranging multigrades such as 5w-40 or 0w-40 is that they save fuel at cruising speeds, and release more power at full throttle. But complications arise……..

Building a good oil

A cave may not be the best place to live, but it’s ready-made and cheap. This is the estate agent’s equivalent of an old style monograde oil. Or you could get Hengist Pod to fit a window and a door; this is moving up to a cheap and cheerful mineral 20w-50. But an architect-designed “machine for living in”, built up brick by brick, is an allegory of a high performance synthetic oil.

It is impossible to make a good 5w-40, or even 10w-40, using only mineral oil. The base oil is so thin, it just evaporates away at the high temperatures found in a powerful engine that is being used seriously. Although there are chemical compounds in there to prevent oil breakdown by oxygen in the atmosphere (oxidation) they cannot adequately protect vulnerable mineral oil at the 130 degC plus sump temperatures found in hard worked turbocharged or re-mapped engines.

Synthetics are the answer. They are built up from simple chemical units, brick by brick so as to speak; to make an architect-designed oil with properties to suit the modern engine.

But sometimes, if you look behind the façade, there is a nurky old cave at the back! This is because the marketing men have been meddling!

The Synthetic Myth

What do we mean by the word “synthetic”? Once, it meant the “brick by brick” chemical building of a designer oil, but the waters have been muddied by a court case that took place in the USA a few years ago, where the right to call heavily-modified mineral oil “synthetic”, was won. This was the answer to the ad-man’s dream; the chance to use that sexy word “synthetic” on the can….without spending much extra on the contents! Most lower cost “synthetic” or “semi-synthetic” oils use these hydrocracked mineral oils. They do have some advantages, particularly in commercial diesel lubricants, but their value in performance engines is marginal.

TRUE synthetics are expensive (about 6 times more than top quality mineral oils). Looked at non-basically there are three broad catagories, each containing dozens of types and viscosity grades:-

PIB’s (Polyisobutanes)

These are occasionally used as thickeners in motor oils and gear oils, but their main application is to suppress smoke in 2-strokes.

The two important ones are:

Esters

All jet engines are lubricated with synthetic esters, and have been for 50 years, but these expensive fluids only started to appear in petrol engine oils about 20 years ago. Thanks to their aviation origins, the types suitable for lubricants (esters also appear in perfumes; they are different!) work well from –50 degC to 200 degC, and they have a useful extra trick.

Due to their structure, ester molecules are “polar”; they stick to metal surfaces using electrostatic forces. This means that a protective layer is there at all times, even during that crucial start-up period. This helps to protect cams, gears, piston rings and valve train components, where lubrication is “boundary” rather than “hydrodynamic”, i.e. a very thin non-pressure fed film has to hold the surface apart. Even crank bearings benefit at starts, stops or when extreme shock loads upset the “hydrodynamic” film. (Are you listening, all you rally drivers and off road fanatics?)

Synthetic Hydrocarbons or POA’s (Poly Alpha Olefins)

These are, in effect, very precisely made equivalents to the most desirable mineral oil molecules. As with esters, they work very well at low temperatures, and equally well when the heat is on, if protected by anti-oxidants. The difference is, they are inert, and not polar. In fact, on their own they are hopeless “boundary” lubricants, with LESS load carrying ability than a mineral oil. They depend entirely on the correct chemical enhancements.

PAO’s work best in combination with esters. The esters assist load carrying, reduce friction, and cut down seal drag and wear, whilst the PAO’s act as solvents for the multigrade polymers and a large assortment of special compounds that act as dispersants, detergents, anti-wear and oxidant agents, and foam suppressants. Both are very good at resisting high-temperature evaporation, and the esters in particular will never carbonise in turbo bearings even when provoked by anti-lag systems.

Must Have MORE Power!

Motorcars are bought for all sorts of reasons, but enthusiasts like lots of power. To get more power, a lot of fuel must be burnt, and more than half of it, sadly, gets thrown away as waste heat. For every litre of fuel burnt, 60% of the energy goes as waste heat into the exhaust and cooling system. A turbocharger can extract a few percent as useful energy and convert it into pressure on the intake side, but only 40-45% is left, and only 25% actually shows up as BHP at the flywheel. 6% goes in pumping air into the engine, 6% as oil drag losses and 2-3% as engine friction. The oil deals with 97% of the friction; so reducing the remaining few percent is not easy. If you doubt that even ordinary oil has a massive effect, take a clean, dry 200 bhp engine, connect it to a dyno and start it up. It will only make 1 bhp for a few seconds. Now that’s real friction for you!

Oddly enough, people get starry-eyed about reducing friction, especially those half-wits who peddle silly “magic additives”, which have not the smallest effect on friction but rapidly corrode bearings and wallet contents. In fact, even a virtually impossible 50% reduction in the remaining engine friction would be no big deal, perhaps one or two bhp or a couple of extra miles per gallon.

Even More Power!

He place to look for extra power is in that 6% lost as oil drag. In a well-designed modern motor, the oil doesn’t have to cover up for wide clearances, poor oil pump capacity or flexy crankshafts, so it can be quite thin. How thin? Well take a look at these dyno results.

A while ago now, we ran three Silkolene performance oils in a Honda Blackbird motorcycle. this fearsome device is fitted with a light, compact, naturally aspirated 1100cc engine which turns out 120+ bhp at the back wheel. The normal fill for this one-year-old engine was 15w-50, so the first reading was taken using a fresh sump-fill of this grade. (The dyno was set up for EEC horsepower, i.e. Pessimistic)

15w-50
Max Power 127.9 bhp @ 9750 rpm
Torque 75.8 ft-lbs @ 7300 rpm

After a flush-out and fill up with 5w-40 the readings were;

5w-40
Max Power 131.6 bhp @ 9750 rpm
Torque 77.7 ft-lbs @ 7400 rpm

Then we tried an experimental grade, 0w-20 yes, 0w-20! This wasn’t as risky as you may think, because this grade had already done a season’s racing with the Kawasaki World Superbike Team, giving them some useful extra power with no reliability problems. (But it must be said, they were only interested in 200 frantic miles before the engines went back to Japan)

0w-20
Max Power 134.4 bhp @ 9750 rpm
Torque 78.9 ft-lbs @ 7400 rpm

In other words, 3.7 bhp / 2.9% increase from 15w-50 to 5w-40, a 2.8 bhp / 2.1% increase from 5w-40 to 0w-20 or a 6.5 bhp / 5% overall. Not bad, just for changing the oil! More to the point, a keen bike owner would have paid at least Ł1000 to see less improvement than this using the conventional approach of exhaust/intake mods, ignition re-mapping etc.

Am I recommending that you use 0w-20 in your Subaru’s? Well, perhaps not! The 5w-40, which is a “proper” PAO/Ester shear-stable synthetic, will look after a powerful engine better than a heavier viscosity “cave at the back” conventional oil, and provide a useful extra few BHP.

The End

However, as with all good things in life, we don’t live in a world of perfect motor cars and therefore we have to look at the lubrication trade-off between longevity, reliability, power and cost, relative to the vehicle in which the oil is being used (a scruffy old XR2i with 192,000 miles on the clock is a very different proposition to your spanking new Impreza). Which is why Subaru (and probably your local dealer) recommends a 10w-50 (Such as PRO S); you could look at a 5w-40 for competition and track-day use, but only the most committed competitor would want, or need, the 0w-20 for the extra 5% power.

John Rowland (Fuchs/Silkolene Chief Development Chemist)

Cheers
Tim
www.opieoils.co.uk

oilman

iTrader: (9)

Probably worth a re-read too

0w-40, 5w-40, 10w-40 and 15w-40 are all the same thickness at 100degC sump temperature 14cst (centistokes).

Centistokes (cst) is the measure of a fluid's resistance to flow (viscosity). It is calculated in terms of the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid.

As viscosity varies with temperature, the value is meaningless unless accompanied by the temperature at which it is measured. In the case of oils, viscosity is generally reported in centistokes (cst) and usually measured at 40degC and 100degC.

So, all oils that end in 40 (0w-40,5w-40,10w-40 & 15w-40) are around 14cst thickness at 100degC.

This applies to all oils that end in the same number, all oils that end in 50 (5w-50, 10w-50, 15w-50 & 20w-50) are around 18.5cst at 100degC and all oils that end in 60 (10w-60, 15w-60 & 20w-60) are around 24cst at 100degC.

That’s a fact…

Now, ALL oils are thicker when cold. Confused? It's true and here is a table to illustrate this.

SAE 40 (mongrade/straight 40)

Temp degC.........................Viscosity (thickness)

0..........................................2579cst
20..........................................473cst
40..........................................135cst
60..........................................52.2cs t
100........................................ 14cst
120.........................................8.8cst

As you will see, there is plenty of viscosity at 0degC, in fact many times more than at 100degC and this is the problem especially in cold weather, can the oil flow quick enough to protect vital engine parts at start up. With difficulty really!

So, given that an SAE 40 is 14cst at 100degC which is adequate viscosity to protect the engine, and much thicker when cold, how can a 0w oil be too thin?

Well, it can't is the truth.

The clever part (thanks to synthetics) is that thin base oils can be used so that start up viscosity (on say a 5w-40 at 0degC) is reduced to around 800cst and this obviously gives much better flow than a monograde sae 40 (2579cst as quoted above).

So, how does this happen, well as explained at the beginning, it's all about temperature, yes a thin base oil is still thicker when cold than at 100degC but the clever stuff (due to synthetics again) is that the chemists are able to build these oils out of molecules that do not thin to less than 14cst at 100degC!

What are the parameters for our recommendations?

Well, we always recommend and oil that gives good cold start protection, by this we mean flow so a 5w will flow better than a 10w and so on. This is why a 5w or 10w oil is about the thickest you want to use except in exceptional circumstances. Flow is critical to protect the engine from wear!

We are also interested in oil temperatures, modifications and what the car is used for. This is related to the second number 5w-(XX) as there may be issues with oil temperatures causing the oil to be too thin and therefore the possibility of metal to metal contact.

This is difficult to explain but, if for example your oil temp does not exceed 120degC at any time then a good "shear stable" 5w-40 or 10w-40 is perfectly capable of giving protection.

"Shear stability" is important here because if the oil shears it thins and that's not good!

However, if you are seeing temperatures in excess of 120degC due to modifications and/or track use there is a strong argument to using a 10w-50 or 15w-50 as it will have more viscosity at excessive temperatures.

There are trade offs here. Thicker oils cause more friction and therefore more heat and they waste power and affect fuel consumption so it's always best to use the thinnest oil (i.e. second number) that you can get away with and still maintain oil pressure.

In most scenarios a decent proper synthetic 5w-30 or 5-40 are the best options, especially for road use all year round.

The Opie Oils Team

ZEN Performance

Run 0w-20 in a Subaru on a track day at your peril!

oilman

iTrader: (9)

We wouldn't recommend it.

New Hondas come out of the factory with it in.

Cheers

Turbovin

iTrader: (2)

I would like to know how many car manufacturers recommend a cold viscosity higher than 5W...I work at the Volvo Engine plant and have a hard time understanding the 15w recommendations, maybe they work fine in the UK but I would never use it here in Sweden.

I always use 5w50 in my Sti Type R. Tried 10w50 but I see no point as the engine wasn't any quieter (it's not noisy at all with 5w either).