oil weight - 0w50 vs. 20w50 .... why use one over the other?
09-29-05, 01:00 PM
#26
He was actually running Redline 40W race oil, which is similar to a 15W40.
The question here was because people were suggesting 20W50 as a part of a larger solution so he stops spinning bearings. I don't think there was any illusions that switching the oil weight was the 'fix' for the issue by itself. There are several other things he's planning on doing as well as possibly changing oil weight. Higher oil pressure, thermo pellet replacement, clearanced bearings are all possibilities.
I told him if people are saying use 20W50, use 0W50 because there's little difference between the two at high temp, and at low temp the 0W will be more useful for lubrication. The car is not strictly a track car, he does have to drive it to and from the tracks/shop to work on it etc.
Also just wanted to say that there's lots of good posts here. I expected the thread to be less useful.
The question here was because people were suggesting 20W50 as a part of a larger solution so he stops spinning bearings. I don't think there was any illusions that switching the oil weight was the 'fix' for the issue by itself. There are several other things he's planning on doing as well as possibly changing oil weight. Higher oil pressure, thermo pellet replacement, clearanced bearings are all possibilities.
I told him if people are saying use 20W50, use 0W50 because there's little difference between the two at high temp, and at low temp the 0W will be more useful for lubrication. The car is not strictly a track car, he does have to drive it to and from the tracks/shop to work on it etc.
Also just wanted to say that there's lots of good posts here. I expected the thread to be less useful.
Originally Posted by Kento
Oh, and I agree with Damon: I doubt that the bearing problems you experienced can be blamed on using a 20W50 oil. 
09-29-05, 01:31 PM
#27
2/4 wheel cornering fiend
Originally Posted by GooRoo
He was actually running Redline 40W race oil, which is similar to a 15W40.
Originally Posted by GooRoo
The question here was because people were suggesting 20W50 as a part of a larger solution so he stops spinning bearings. I don't think there was any illusions that switching the oil weight was the 'fix' for the issue by itself. There are several other things he's planning on doing as well as possibly changing oil weight. Higher oil pressure, thermo pellet replacement, clearanced bearings are all possibilities.
Originally Posted by GooRoo
I told him if people are saying use 20W50, use 0W50 because there's little difference between the two at high temp, and at low temp the 0W will be more useful for lubrication. The car is not strictly a track car, he does have to drive it to and from the tracks/shop to work on it etc.
If he's concerned about lubrication at low temps, I'm not so sure he needs to drop to a 0W oil. I don't see a reason why a 10 or 15W multi-vis oil shouldn't be fine for low temp operation.
09-29-05, 03:09 PM
#28
Originally Posted by Kento
It may be "similar to a 15W40", but it's still been categorized as a straight grade oil, regardless of its low temp viscosity properties. I'm assuming that he ensured the engine and its oil were up to proper operating temps before ever getting on the throttle...
Originally Posted by kento
Before experimenting with all these options, he needs to be sure that he has ruled out all other possible causes besides a oil pressure/bearing clearance issue.
Originally Posted by kento
Hmm, I'd still be wary of using an oil that has such a wide viscosity range, even if it is synthetic. You still have to add a bunch of additives to get that wide a range, leaving less room for the base stock, which really does most of the work.
If he's concerned about lubrication at low temps, I'm not so sure he needs to drop to a 0W oil. I don't see a reason why a 10 or 15W multi-vis oil shouldn't be fine for low temp operation.
If he's concerned about lubrication at low temps, I'm not so sure he needs to drop to a 0W oil. I don't see a reason why a 10 or 15W multi-vis oil shouldn't be fine for low temp operation.
Based on what I've read, the reason a 10W or 15W isn't low enough is that even a 0 isn't low enough. No oil available is low enough for ambient temp lubrication. A working engine wants between 5 and 20 cS viscosity to flow (and therefore lubricate) properly at pressure. Even a 0W oil is 40cS at 75 degrees which is too high. But that compares to the 15W oil at 85cS (again at 75 degrees) which is substantially worse.
09-29-05, 04:24 PM
#29
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Originally Posted by Kento
(IIRC, in the other thread, one poster who spoke to a Formula Mazda engine builder said they must do complete rebuilds every race. Whether this is the result of their using 0W oils is obviously open to question, but the fact is there.)
They don't know if it was the oil or the other changes but for whatever reason they are not going to experiment to find out.
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/mixing-10w30-5w30-447759/page5/
ed
09-29-05, 04:58 PM
#31
2/4 wheel cornering fiend
Originally Posted by GooRoo
Based on what I've read, the reason a 10W or 15W isn't low enough is that even a 0 isn't low enough. No oil available is low enough for ambient temp lubrication. A working engine wants between 5 and 20 cS viscosity to flow (and therefore lubricate) properly at pressure. Even a 0W oil is 40cS at 75 degrees which is too high. But that compares to the 15W oil at 85cS (again at 75 degrees) which is substantially worse.
09-29-05, 05:36 PM
#32
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My buddy runs straight 50w in his 1st gen race car, BUT all clearances in that motor are on the loose side of spec. Additionally, that engine is never run when it is cold outside.
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