Can too thick of oil be damaging?

[OVERKILL]

Originally Posted by StevieC
It may allow 20w50 but it might not be optimal for bearings. The reason they "allow" it is because there might be limited choices in certain parts of the world and the trade off could be minor wear/tear that results in using a less optimal thickness of oil. I'm talking 5w30 to 20w50 sort of scenario.


Based on Shannow's significant presentation on bearing design and operation, my takeaway is that you can't really go too thick on the bearings (within reason based on the W rating relative to ambient). They are self-regulating via side leakage and if anything a thicker oil just provides a more generous MOFT. What you do end up with is some more heat generated by the heavier oil as a result of friction, higher load on the oil pump drive assembly and higher oil pressure as an artifact of resistance to flow.

Conversely, to accommodate thinner oils there have been changes to bearing design which increase friction somewhat. The primary modification is bearing width as a lower MOFT can be counteracted via a wider interface.

 

[StevieC]

Originally Posted by hatt
If they list xw-20, xw-30, xw-40, and xw-50 please explain how you know which ones are speced and which ones are allowed?

They will usually put the recommended grade in the owners manual that no one reads and also on the oil cap. Further in an owners manual if you have never read one it will have a chart similar to above or list other appropriate oils that may be used if the recommended grade isn't available. Some go as far as to list a temperature chart as well. You should really read some of the manuals online in PDF format for popular vehicles.

 

[StevieC]

Originally Posted by OVERKILL
Originally Posted by StevieC
It may allow 20w50 but it might not be optimal for bearings. The reason they "allow" it is because there might be limited choices in certain parts of the world and the trade off could be minor wear/tear that results in using a less optimal thickness of oil. I'm talking 5w30 to 20w50 sort of scenario.


Based on Shannow's significant presentation on bearing design and operation, my takeaway is that you can't really go too thick on the bearings (within reason based on the W rating relative to ambient). They are self-regulating via side leakage and if anything a thicker oil just provides a more generous MOFT. What you do end up with is some more heat generated by the heavier oil as a result of friction, higher load on the oil pump drive assembly and higher oil pressure as an artifact of resistance to flow.

Conversely, to accommodate thinner oils there have been changes to bearing design which increase friction somewhat. The primary modification is bearing width as a lower MOFT can be counteracted via a wider interface.


I don't doubt that. I would run a few UOA's at the recommended oil for a base line and then play around and see how it affects the wear metals to make an educated decision. Not just use a thicker oil because of the "Thickie" crowd here thinks they know better than the engineers that designed the engine or because it's "allowed" according to the chart in the owners manual. Which again might be allowed but less than optimal. Show me evidence that it provides better wear protection / longevity and not increased wear and I will jump on the band wagon. It's the hearsay that drives me nuts. "I think a 30wt" is better, or this is what they use in Australia so I'm good. No show me it.

I myself once break in is over on my Toyota will run a few baseline UOA's on the 0w20 and then step it up to a 0w30 and see what that gets me. Both Winter/Summer for comparison under both conditions. That is how it should be done. Not by the "Feeling" or "Because the thickie crowd told me so"

My Journey operated as a fleet vehicle which used to be spec'ed as a 5w30 ran beautiful UOA's on 5w20 in really hot summers and very cold winters with short trip driving mixed in and multiple re-starts. I didn't get a chance to do a run with a 30wt to see that UOA before it was totaled but the 20wt UOA's were so good that there wouldn't have been a need to change or risk the warranty by using something Chrysler didn't specify in the manual. (No chart in that manual)

Not pointed at you Overkill, just in general as a sideline to your post back to me.

 

[hatt]

There are two charts listed on this page. All grades are recommended grades. Certain grades are recommended if you're worried about slightly better fuel economy.

 

[OVERKILL]

Originally Posted by StevieC
I don't doubt that. I would run a few UOA's at the recommended oil for a base line and then play around and see how it affects the wear metals to make an educated decision. Not just use a thicker oil because of the "Thickie" crowd here thinks they know better than the engineers that designed the engine or because it's "allowed" according to the chart in the owners manual. Which again might be allowed but less than optimal. Show me evidence that it provides better wear protection / longevity and not increased wear and I will jump on the band wagon. It's the hearsay that drives me nuts. "I think a 30wt" is better, or this is what they use in Australia so I'm good. No show me it.


I don't think our typical Blackstone UOA is going to have the resolution to discern that nuance, which is a topic we've discussed ad nauseam.

Neither crowd "knows better". Engines are extremely tolerant of varying grades as evidenced by the specs around the world and the ranges given in the manuals. It is highly likely that it isn't one oil that is "optimal" but rather a reasonable range that is appropriate for the given conditions and these charts pretty much support that. If you aren't going to be seeing 120 degrees ambient, the 20w-50 is probably not going to be within that optimal range for an engine that specs 0w-20 under more "typical" conditions. And of course one can reverse that.

It's like the Ford 5w-20/5w-50 game. The 5w-20 is optimal for typical street use the 5w-50 is optimal for the track. But they for whatever reason, couldn't spec both (like GM does/did with the Corvette and 5w-30/15w-50). So if you used a non track pack at the track you were outside the optimal range for the lubricant and had to rely on temperature activated safeties to preserve your bottom-end. If you had a track pack and primarily used it around town you were using an oil that was overly viscous for that usage pattern and subsequently burning more fuel than necessary (as minute an amount as that might be) and had excessively generous reserve for temperatures that were not going to be experienced.

Would a 0w-40 (or 5w-40) have been a good compromise or a Euro spec 0w-30/5w-30? Also perhaps. Dodge appears to feel it is OK for a tracked 707HP mill and GM has moved to it with the Corvette.

There really is no single answer. Every vehicle is driven differently and so that range of reasonable compromise is going to shift one way or the other. Following the manual is the no-brainer solution barring the resources to perform extended tear-down testing or at least trying to correlate viscosity selection with oil temperature tracking. It's a fun game, but as you yourself have demonstrated, using a quality lubricant at a sane interval will result in something else happening before anything pertaining to lubricant selection becomes evident with the engine in most cases.

 

[hpb]

Originally Posted by FordCapriDriver
Some people in this board think that pouring 20w50 in your engine is about as good as pouring sand into it.


Exactly! Drives me crazy. 20w50 went into "everything" here 20 years ago, and engines weren't grenading into a million pieces.

These days, 10w40 is our go to oil, where the same vehicle in the US would be spec'd for 0w20 - again, engines are living long and healthy lives, even with 15,000km (9,200 mile) OCI's specified by just about every manufacturer for Oz vehicles...

 

[Silk]

I'm off the recommended chart...it still runs, no loss of power or increased fuel consumption. When it comes to a shuddering halt, I'll report back here ASAP.

 

[ndfergy]

Originally Posted by OVERKILL
There really is no single answer. Every vehicle is driven differently and so that range of reasonable compromise is going to shift one way or the other. Following the manual is the no-brainer solution barring the resources to perform extended tear-down testing or at least trying to correlate viscosity selection with oil temperature tracking. It's a fun game, but as you yourself have demonstrated, using a quality lubricant at a sane interval will result in something else happening before anything pertaining to lubricant selection becomes evident with the engine in most cases.


BINGO

That's why I generally avoid making recommendations. Not that I'm qualified to do so anyway.

 

[RDY4WAR]

What about on cold starts? On a 50 degree morning, a more viscous 20w-50 would take longer to circulate to the top of the engine than a less viscous 10w-30, correct? If that is correct, wouldn't that contribute to more long term wear?

 

[Shannow]

Originally Posted by StevieC
They "Allow" a 50wt not "Spec" a 50wt. There is a difference in what I said.

Why isn't it the other way around ?

They ALLOW 20 grades in CAFE world, but SPECIFY 30 grades in non CAFE countries.

E.G. GM, who specify ILSAC Dex 1 (economy) grades in the US, but in Oz, your warranty is CONTINGENT on running Dex 2 for exactly the same engine

 

[OVERKILL]

Originally Posted by RDY4WAR
What about on cold starts? On a 50 degree morning, a more viscous 20w-50 would take longer to circulate to the top of the engine than a less viscous 10w-30, correct? If that is correct, wouldn't that contribute to more long term wear?


The whole purpose of the W rating is to indicate the suitability for the Winter temperature one is going to experience. 50 degrees is not cold and the 20w-50 would flow just fine. That said, with low ambient temperatures, a 20w-50 is likely not an ideal choice as high oil temperatures are unlikely unless you drive like Mario Andretti.

Remember, oil pumps are positive displacement. They don't care if it is 20w-50 or 0w-20, as long as it can be sucked into the pump, it is going to move roughly the same amount per rotation. In fact, assuming we aren't on the relief, you'll have less leakage through the pump with the heavier oil.

 

[Shannow]

Originally Posted by StevieC
It may allow 20w50 but it might not be optimal for bearings.


I'm interested whether this statement comes from spitballing and conjecture (might), or from an understanding of bearing operating parameters and design.

Interested in your take on the Sommerfeld number versus MOFT and side leakage with respect to your statement, and how within the range of automotive engine oil viscosities it will lead to anything but a slight reduction in brake horsepower and economy...


Originally Posted by RDY4WAR
Can excessive viscosity accelerate bearing wear due to increased shear and heat?


Not if you are buying it as engine oil...there's industrial viscosities that you simply wouldn't use, but not any engine oil you are going to find.

If you get the wrong "W" rating for your ambient, then yes, but tht's an entirely different issue.

 

[RDY4WAR]

What about areas that don't see direct pressure from the pump such as cylinder walls / rings and cam lobes?

 

[Shannow]

Originally Posted by OVERKILL
Originally Posted by RDY4WAR
What about on cold starts? On a 50 degree morning, a more viscous 20w-50 would take longer to circulate to the top of the engine than a less viscous 10w-30, correct? If that is correct, wouldn't that contribute to more long term wear?


The whole purpose of the W rating is to indicate the suitability for the Winter temperature one is going to experience. 50 degrees is not cold and the 20w-50 would flow just fine. That said, with low ambient temperatures, a 20w-50 is likely not an ideal choice as high oil temperatures are unlikely unless you drive like Mario Andretti.

Remember, oil pumps are positive displacement. They don't care if it is 20w-50 or 0w-20, as long as it can be sucked into the pump, it is going to move roughly the same amount per rotation. In fact, assuming we aren't on the relief, you'll have less leakage through the pump with the heavier oil.


Per the pic...oil gallery filling time and rocker arm oiling time are the same...provided that the oil is in it's pumpable range.

Drop below the temperature appropriate for the "W" rating, and it's slower getting there.

That being said, the majority of the wear is in the initial operation coming to temperature, not the few seconds that it takes the oil to get there. The parts are already coated in a highly viscous layer at initial turnover/

 

[OVERKILL]

Great info as usual Shannow.

 

[Gasbuggy]

Originally Posted by Motorking
Absolutely. Thick oil will not get into the tiny bearing clearances of modern cars, causing way to much heat and bearing wear. I once put 20w50 mobil 1 in my CTS-V that called for 5w30. It went into limp in mode while driving at freeway speeds and oil temp shot up to 245 degrees



Assuming you had a gen 1 V since you know the exact temperature, though 245 shouldn't cause limp mode. I noticed my oil temps on my old V going up when I switched from 5w30 to Rotella T6 5w40. Didn't have that issue with Mobil 0w40 though.

 

[Shannow]

Originally Posted by RDY4WAR
What about areas that don't see direct pressure from the pump such as cylinder walls / rings and cam lobes?


See above...if it's pumpable, it gets there around the same time.

But if you've ever pulled an engine apart you'll see that the pistons and rings, and cam/lifter interface is wet with oil

 

[RDY4WAR]

Great info. Thanks for all of the replies so far.

I've torn down and built several engines. Earlier this year, I had to rebuild an engine I'd built a few years ago. It only had 18k miles on it. It was a 306ci SBF. I built it a little tight with .0020" main and .0018" rod bearing clearances. I recommended 10w-30. He didn't take my recommendation and ran VR1 20w-50 with Lucas oil stabilizer instead. He brought it back for a rebuild because he cut open his filter and found a lot of shavings. It still held 40 psi oil pressure at hot idle with no knocking. When I tore it down, 4 out of the 5 main bearings had spalling. Those same bearings had discoloration but no scuffing, uneven wear, or anything that would indicate metal to metal contact. The crank wasn't out of round. I put new bearings in, along with new seals and gaskets, and sent it back out. I took into consideration that he wasn't going to run anything but 20w-50 so I opened up the clearances to .0028" and .0026". I still am not sure what caused the bearings to spall but have been curious if the oil viscosity being too high for the clearances was a contributing factor.

 

[Shannow]

Given that the oil has to pass through the mains to get to the big ends, and they weren't starved, I'm not sure either...if the big ends were hurt too, I could see it.

Had a mate back in the day with a Falcon ute and 302 Clevo and 4 speed.

After a movie (for example), he'd come out, back out of the carpark, and straight into a burnout...all on BP Corse 25W50...he never had any issues, in spite of being insane.

 

[OVERKILL]

Originally Posted by RDY4WAR
Great info. Thanks for all of the replies so far.

I've torn down and built several engines. Earlier this year, I had to rebuild an engine I'd built a few years ago. It only had 18k miles on it. It was a 306ci SBF. I built it a little tight with .0020" main and .0018" rod bearing clearances. I recommended 10w-30. He didn't take my recommendation and ran VR1 20w-50 with Lucas oil stabilizer instead. He brought it back for a rebuild because he cut open his filter and found a lot of shavings. It still held 40 psi oil pressure at hot idle with no knocking. When I tore it down, 4 out of the 5 main bearings had spalling. Those same bearings had discoloration but no scuffing, uneven wear, or anything that would indicate metal to metal contact. The crank wasn't out of round. I put new bearings in, along with new seals and gaskets, and sent it back out. I took into consideration that he wasn't going to run anything but 20w-50 so I opened up the clearances to .0028" and .0026". I still am not sure what caused the bearings to spall but have been curious if the oil viscosity being too high for the clearances was a contributing factor.


Well Lucas is nothing but a thickener with zero additives in it so I guess it's possible there was some pump cavitation

What kind of pump did it have in it? stock or an HV or HV/HP? My experience with Windsors is that a stock pump is all they need.