micared

Hi, I'll try to answer your points as I reach them........

you own a U.K. car, and let the dealer handle it ....in my experience, reason enough to be worried, unfortunately.....

........degree of banter, accepted, missed the signs in the heat of battle However, the halfwit comment was justified, under the circumstances.

I'd be interested to see how Davids recommendations tally with your own.

Again, letting MY local Subaru dealer work on your car is tantamount to telling them that you want it to come back with a fault it didn't have prior to them touching it. No security from fools there, more's the pity.

Last paragraph in my second to last post may have been lost on you. Hardly the outlook of someone defensive to remind others that I've never said it wasn't an open forum, and that you shouldn't post your opinions.

Ultimately, my opinions may be the same as yours. However, your suggestion that using the safest sounding method to change the oil is comparable to " touching wood , and throwing salt over your shoulder ", is, imo, patronising at best, and misleading at worst. Sorry. You have yet to bring to our attention any information which directly contradicts the idea that the safest method used by some people is unnecessary, and, while asking questions is laudible, answers would be of more use. Until they are forthcoming, I'd imagine that the ' superstitious ' among us will continue to waste our time trying to avoid having our wallets emptied.

If the oil change is symptomatic, as you suggest, why is there no history of failings after changing the oil and filter using the safe procedure? Unless I'm missing something obvious ( and I am knackered ), this, surely, is the point at which we need an answer, and not a question. Certainly, in my time on the board, I've yet to see someone complaining that their engine has lunched itself under these circumstances......this seems to fly directly in the face of your suggestions, given that it's been well documented how many have let go just after an oil change that has not followed this procedure.

You'll be unsurprised to learn that I'm no engineer, which is why, after having observed the various posts from several, clearly informed, people on this board for a period of months, drew what conclusions I have. They may turn out to be wrong, but, fortunately, if so, I won't have done my engine any harm by doing what I do to try to protect it.

Absolutely agree with you about one thing, that being your comments on new ideas.

If this lot doesn't cure everyones insomnia, nothing will!

Jiggerypokery

I haven't actually looked at where the spark plugs are, but I was wondering, if the area around the spark plugs is dirty / dusty, isn't there a danger than some dirt could get sucked in when they are removed? I know this isn't the same as dirt coming through the intake, but could it cause any damage?

Adam M

ok sprint chief,

all I am saying is that it is irresponsible to disuade someone from doing something that can do no harm if there is chance it can save them from a big end bearing failure.

With regard to your questions, yes a friend and I (Pat) have done the calculations for the bearing size of the subaru engine and theoretically the oil film shear strength isn't sufficient in even the best of oils to withstand the force being applied by means of some of the engines we have seen.

The longer stroke of the 2.5 sti is the better bet as it applies less force in order to deliver this torque.

The oil will only stay in place if the shear strength is greater than the force applied by the con rod.

I would rather not rely on the shear strength to ensure that the bearing doesn't pick up, I would rather only crank the engine when I can be sure that any displaced oil has sufficient pressure behind it to be replaced.

I agree it is only conjecture, but your conjecture that it could be a symptom rather than a cause doesn't make a suggestion as to how to avoid it. The general consensus of this procedure is based on it being causal but as has been said before, so what? It can't hurt but it might help.

you saying it might not be the real problem so don't waste your time is still a foolish statement with hundres of thousands of pounds worth of engines hanging in the balance and a spate of unexplained big end bearing failures following oil changes.

When someone is in a position to say unequvicably what the problem is and demostrate it with evidence, then it would be ok to dismiss this belt and braces approach, until then, the sensible thing to do, is to spend an extra 5 minutes doing the service as descirbed above.

kwakman

Dont let engineering judgement get in the way of scooby folklore! The oil change procedure subject goes back to the old scooby testament so the keyboard disciples will hurl insults at anyone who might dare to question the wisdom behind it.

I have tried wet cranking with the crank sensor out but didnt manage to get the o.p. light to extinguish. Whats the cranking speed on a scoob? 50 rpm? Is that sufficient rot speed for the pump to generate enough oil pressure to convince the sensor all is well? I'll stick with the prefilled filter and sensor out approach cos it doesnt take much extra time, but find it difficult to believe doing it this way or another would directly cause big end failure.

I know of one case where the correct procedure was followed and the engine failed a couple of hundred miles later, but as this is an isolated case and I strongly suspect no meaningful failure mode analysis has been carried out on such events, it doesnt mean much.

Sprint Chief

OK I think some of my earlier posts might have been a little misunderstood That may have been more to do with the way they were written than anything else... note to self, always read the post before submission!

Just to make it clear, I'm not suggesting people don't go for belt and braces, I'm just trying to open up the engineering debate. Perhaps my throwing salt over the shoulder comment was a bit out of line Made you all pay attention though

Without a decent (controlled) statistical analysis of the failures we can't really work out much. Even that would need to be done with care - I'm sure those who take a lot of care over their oil change also take a lot of care over what fuel and octane boosters they use, etc. etc. - and since we know det can cause big end failures, it would become difficult to separate out exactly all the causes.

While it is right to say if we don't understand it is best to adopt belt and braces, my point (not very well made) should have been that if we are only addressing a symptom, rather than the root cause, we really should be searching for this instead, because finding this might be the only "real" way of protecting the hundreds of thousands of pounds worth of metal you describe!

Adam, you point out you have done the calculations for the Subaru engine but are these calculations at peak power, fast idle or at engine crank speed? All are very different conditions. Starting up after an oil change is going to relate to cold cranking, where the problem could be failure to generate sufficient hydrodynamic pressure due to bearing surface speeds (more a function of the bearing diameter than the width), or after the initial firing where we go to a fast idle situation, where the surface speed will be fine but the loads will still be light (even compression loads will be low as the engine will be operating on a partial vacuum at this stage).

The rod loads here will be small compared to the loads experienced at peak power, so the peak torque or power calculations aren't really relevant. Also we shouldn't see any difference between high power output engines and standard lower output engines using the same bearing design - again something for which some statistical analysis would be necessary to grasp.

In addition, if the rod load is sufficiently high to break through the oil pressurised by the hydrodynamic action of the bearing, any additional pressure provided by the oil pump is going to be down in the noise - the bearing will still pick up.

Note journal bearings do not really need a moving or pressurised supply of oil to perform their function as bearings, they could just sit in their own reservoir, the main function of moving oil through them is to prevent them from overheating.

On the other hand, I have access to some freeware CFD tools at work... if only I had the time to set up a few experiments! Perhaps next year...

scoobyboy

so why does this big end failure not happen to legacys or forester turbos in the same quantitys that it does to imprezas? we all know theres less compression on cranking a turbo than a n/a car, so surely a n/a car cranking puts more load on the bearings yet theres hardly any n/a cars with big end failure it's all turbos. so if it's because of a poor oil change then every subaru out there would be having a new engine fitted wouldn't it? of course it could just be that impreza turbos get a good hammering more often than the other models so the problem arises more frequently.
imo i don't think the problem is down to how the oil is changed, by all means fill the filter up it is good practice and disconnect what ever you want but if it's going to blow up it will.

Gear Head

iTrader: (2)

Guys, at the end of the day, it doesnt take long to dissconnect the crank sensor and prime the filter does it? Atleast if you do this, and motor does go bang soon after, you know in your mind that it wasnt down to the way you changed the oil. Common sense really, especially as engines have failed in this situation and a cause has not been found. Maybe then we can put this issue to bed!!!

micared

If disconnecting the crank sensor / removing the plugs isn't necessary, why does no-one ever come on here saying that their car's just blown up even though they've done this? Seems to me that the only people who have failures just after an oil change either didn't do the above, or aren't sure if it was done or not because they didn't see the car being serviced. Anyone who has had a failure just after an oil change, and did the above, please say so!

scoobyboy

so why is it turbos that only seem to suffer then dealers dont just service them and i can't see them changing the way they service them to the way they service legacys or foresters so why don't they blow up? i don't think we are looking at the bigger picture only a small part of it.

WR1 Ant

Done mine last sat at 3000 miles (half way between 1000 mile 1st service and 5000 mile oil change its a wr1) cost less than £23 for genuine oil filter and sump washer and 4.5L of castrol 10/40 magnatec (used this oil as its what my dealer uses as i wanted to use the same) will go to dealers for the 5000 mile one so I keep all the service history ok will then do one myself at 7500 miles midway between the official oil changes so the oil will get changed every 2500 miles.

micared

I agree that it's interesting that legacys and foresters don't seem to be affected, and I take your point that imprezas probably get more right foot than the others. Do legacys and foresters run as much bhp/torque as a u.k. spec impreza? Or are there any other significant mechanical differences? Don't know much about either of them, tbh. Still think it's relevant that no-one ever says that their impreza has grenaded just after a ' safe ' oil change though......it's nearly always quite soon after an oil change that's disregarded this. Still can't see the point in not disconnecting the crank sensor either.....it may help, and it certainly isn't doing any harm.

ALi-B

iTrader: (1)

A little point about this oil change procedure I'd like to make.

The fact that you do it the "advised" way by no means guarantees that you never ruin your engine.With the syndrome of engines blowing shortly after an oil change is no new thing, and it's not a Subaru thing either.

Why? Because the engine was already on its way out anyway, be it through wear, bad servicing, duff oil pump/pressure relief. Previous starvation/oil surge or heavy engine knock or some other fault....the momentary oil starvation after starting just finished it off.

I say this as the most likely time for engine to go is after a oil change, and not priming the lubrication system (or less than 1000miles). Not priming didn't cause the engine to expire but most certainly finished it off.

So priming the lubrication system by filling filters and cranking, will prolong the life of an engine that is on borrowed time. I don't argue against it, as it will never do any harm.

If it gives piece of mind, and seeing that Scoobs do seem to be prone to this. For the sake of a few minutes do it.

But on the other hand, I'd like to speculate that if every Subaru made had the oil changed using priming/filling filter method. I would be certain many engines would still expire.

micared

Btw, kwakman, why bother with the " keyboard disciples will hurl insults " comment, and then contradict your own criticism of them by doing what they do during an oil change? Seems to me you agree with " the wisdom of scooby folklore " that there is a risk, otherwise why do it? As I understand it, you're Sprint Chiefs brother....priceless that you come on to defend him, but don't take his advice seriously enough to disregard the ' safe ' oil change procedure. Not meant to be argumentative, and apologies if any of the above is factually incorrect!

Don't think anyone could ( yet ) be accused of 'hurling insults' at each other! Still, with threads like this, it's usually only a matter of time.

Interested to hear other views on the ' imprezas blow up because of the way they're driven ' theory.

ALi-B, no-one is suggesting that this oil change method is the key to eternal life.... as you say, just a means of helping to prolong it. And if all Scoobs did have their oil changed in this way, and still expired, at least we'd know for sure that the oil change procedure wasn't a possible issue. By doing it this way though, you eliminate a possible cause of damage, however slight that risk may turn out to be, and without any negatives to take away from the positives. Tbh, i've got so used to doing it this way now, I'd find it hard not to.

Andrew Timmins

Could someone please explain something to me?

If you leave your car to stand overnight, most of the oil will drain back to the sump. When you start the engine it will take a few seconds for oil to circulate and for normal pressure to be attained.

If you change your oil and don't prime the filter I can see that there would be a delay in the oil circulating whilst the filter is filled. This part of the procedure I can understand.

If you change your oil and prime the filter would the oil not be circulating round the engine just as soon as if you made a normal cold start?

I'm probably missing something obvious, so could you tell me what?

pslewis

Andrew - I see your point and rightly made, BUT the 'Old Women of Scoobynet Policy' in this situation is every morning to disconnect the Crank Sensor and turn the engine over, run round the car singing the Scooby-Doo theme tune (CLOCKWISE mind you!!), re connect the Crank sensor, get into car, kiss the crucifix and pray solemly as you turn the key.

You are quite right that theres not much difference in just starting the engine after an oil change and starting it on a winters morning after the oil has retired to sump over 12 hours! Remember that the filter is primed after the oil change (I have never said put an empty filter on)

Pete

jjones

oil pick up pipe old man.

have you ever heard a car start directly after an oil change? i can assure you it sounds nothing like it does first thing in the morning.

Patriot

Now thats what I really need, a pit in my garage, the answer to all my troubles working on cars. Must look at the possibility of digging one out.

Martin

easyrider

Has anyone thought of the possability that its not a problem with oil flow/pressure,but more of a case of air in the circulation system after an oil change-even if you prime the filter,theres still a little slug of air in the channels before and after the filter.
Thet shear of the oil sitting in the bearings should-and i emphasise should, be able to cope with it being cranked,but what with the bearings being quite small,when that little slug of air is introduced to them,gets shot of the small film of oil,it then causes metal to metal contact.
This theory will irradicate the "12 hours overnight" theory,as no air is introduced into the system,no matter how long the engine has been left standing.

Whats your thoughts?

Gary

scoobyboy

if say we take a forester turbo and an impreza turbo and compare them what differences do we come up with? we know theres a difference in ecu's as far as fueling,timing and so on but mechanically they are the same yet the forester does not blow up so what else is there that can be causing the problem? i take it the oil pumps are the same as also pistons,crank,conrods. must admit i've never had the engine out of a forester so can't confirm this but maybe some else can.

micared

Great reply, pslewis, spectacular ignorance displayed in one post.....in all honesty, are you on one of your wind-ups, or is that a serious reply?