10W vs 10W-30 vs SAE 30 cylinder wear

[JAG]

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My opinion is that straight weight oils are viable only in engines that get lots of continuous hours...

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Trying to figure out lubrication based on imagining what's going on in an engine is what's got so many people misled about what's going on. This is a science and engineering subject and must be approached using the tools of those trades: testing and modeling.

Case in point: wear rates are highest during less than full operating temps. It's been proven through testing so many times. The fatal error that gets committed is attributing this to the oil being too thick. That's an imagination.

Case in point: fatal error of thinking that kinematic viscosity is the viscometric quantity that provides engine protection. Nope, kinematic viscosity is the viscosity at nearly zero shear rate, at atmospheric pressure, and some temperature. Those conditions are not present in bearings and cylinder walls where shear rates and pressures differ dramatically from those in the kinematic viscosity test.

Kinematic viscosity also can't predict cold cranking and cold pumping viscosities, for similar reasons.

 

[G-MAN]

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More data here: 1st slide of Page 6. Effect of viscosity on shear strain rate. The 30 wt oil is nearly Newtonian while the 20W-50, having polymers, is a psudoplastic Non-Newtonian fluid. In this chart, above some shear rate, the 30 wt. is more viscous than the 20W-50. Take this as an example, NOT a universal trend with all straight 30 wts and all 20W-50 oils.

Newtonian fluid means the viscosity is constant as shear strain rate varies.

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There ya go...and that's the crux. As good as VI improvers have gotten, and they are now light years ahead of what they used to be, they still are not in and of themselves lubricants. They "fool" the oil into behaving like a thicker oil at higher temps under static conditions but under high temp AND high shear this viscosity "sleight of hand" can't match the characteristics of a Newtonian straight grade, it can only approximate it. And it's at that point of approximation where the EP/AW additives are critical. Thus with a 5w30 and an SAE 30, both with the same HTHS vis of, say, 2.9, the SAE 30 will I believe offer greater protection because the HTHS vis of the SAE 30 is a product of the oil itself. For the 5w30 it's the product of the oil and a substance that offers no inherent lubrication at the molecular level. And the reason wear at that point is not excessive is because of the advanced EP/AW additives used in modern multi-grade oils.

If you look at the ZDDP additive levels for straight grades 30 years ago you would think the add pack looked weak. But straight grades simply don't require the level of EP/AW additives that multi-grades do to offer equal or better protection. Modern multi-grade oils can perform at the levels they do because of a carefully designed balance between base oils and and EP/AW additives. Over five years ago moly was just starting to be seen in a few PCMOs. Now its use is almost a given, and if not moly something else is used like boron or overbase calcium to work synergistically with ZDDP to "carry the load" that these thinner and thinner oils could not do on their own. Does this "carefully designed balance" work? Without question. I think I've shown that over the last few years with the stellar 5w20 UOAs from my Chrysler. But as we've seen in the Audi RS4, engine designers can come up with things that even the best multi-grade oils can't handle. These oils fail to protect precisely at their weakest link, that "approximation" of high viscosity, where "the real thing" is needed not a viscosity "sleight of hand."

 

[JAG]

Amen, G-MAN!

 

[G-MAN]

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More data here: 1st slide of Page 6. Effect of viscosity on shear strain rate. The 30 wt oil is nearly Newtonian while the 20W-50, having polymers, is a psudoplastic Non-Newtonian fluid. In this chart, above some shear rate, the 30 wt. is more viscous than the 20W-50. Take this as an example, NOT a universal trend with all straight 30 wts and all 20W-50 oils.

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Here's the slide:

 

[G-MAN]

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Some of Valvoline's SAE 30 specs are better:
VI = 113
Pour Point = -17F

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I'm having a hard time believing that Valvoline is not using at least some VII's -- with a VI that is up around 113. Schaeffers 7000 (mixed with PAO) only has a VI of 105.

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VI is not just the product of the VI of the base oil plus VI improver. Additives, especially if the carrier oil is high VI esters, can have a positive effect on the VI of the finished oil. PPDs can affect the VI, too. I think that's what is happening with the Valvoline SAE 30.

 

[buster]

Thanks G-Man. Great post.

 

[yannis]

Just for the record it like to comment that the right word is pseudoplastic , not psudoplastic .
pseudo has the meaning of not genuine; fake

 

[Curious Kid]

When I first viewed the graph results on the opening page, I recalled the limitations placed on 2-cycle diesel engines, in that straight weights are to be utilized. Apparently a multi-weight oil does not have time to recover between combustion loads for the amount that it shears when used in place of single grade oils, resulting in increased wear. I wish I took more interest in the reasoning/facts rather than just buzzing through and concluding, "Interesting". Such info would seem beneficial to this thread.

Where I'm confused is that I was into thinking that with the increase in VI due to VII's, the reduction in viscosity thinning as temps increased and whose oil had a "decent" HTHS value, would make it better than a single weight/grade oil.?.

I sense some understanding is being turned on end!?!

Good stuff.

Take care.

 

[TallPaul]

This is a great thread. In the chart G-Man posted, I am suprised 20w50 didn't hold up better. I was thinking that a SAE30 could classify as 20w30 and so a 20w50 would be like a SAE30 with some VII. Thus it should hold up as well under sheer, but apparently the VII interferes with HTHS, or more likely the 20w50 is based on something thinner than SAE 30.

I have visions of a whole forum for straight grade oil discussions.

Maybe I'll run a SAE 40 in my F150 next summer.

 

[G-MAN]

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When I first viewed the graph results on the opening page, I recalled the limitations placed on 2-cycle diesel engines, in that straight weights are to be utilized. Apparently a multi-weight oil does not have time to recover between combustion loads for the amount that it shears when used in place of single grade oils, resulting in increased wear. I wish I took more interest in the reasoning/facts rather than just buzzing through and concluding, "Interesting". Such info would seem beneficial to this thread.

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You've summarized the salient points rather well re why 2-stroke diesels require straight grade oil over multi-grade. With a 2-stroke the rod bearings never see a "rest period" since every downward stroke is a power stroke. With a 4-stroke every other downward stroke is a power stroke.

 

[buster]

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AMSOIL ACD is formulated without viscosity index improvers (VI). This shear stable formulation stops viscosity loss and associated bearing and cylinder bore wear.

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Amsoil ACD PDS mentions this.

 

[buster]

So ideally then, in high stress applications, the lower the VI, the better correct? Although using mostly all high vis PAO's/Esters could still give you a high VI with little VII's.

 

[bruce381]

Hey Gman maybe for winter you can PP depress the ---- out of the oil for decent winter performance send me 4 ounces and lets see if I can get the PP down some more.
bruce

 

[bruce381]

Bye the way the add pak and PPD will raise the VI some so a VI of 117 or so is perfectly OK and to me means NO VII at all.
bruce

 

[G-MAN]

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So ideally then, in high stress applications, the lower the VI, the better correct?

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That's my take on it. Remember back in the late 70s, early 80s when GM nixed using 10w40 because of premature cam lobe failure? This is why.

 

[G-MAN]

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Hey Gman maybe for winter you can PP depress the ---- out of the oil for decent winter performance send me 4 ounces and lets see if I can get the PP down some more.
bruce

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I bought a gallon of Amsoil ACD SAE 30 from Pablo and was planning to mix it either 80/20 or 60/40 to do just that. What did you have in mind?

 

[buster]

I might try and test a good 10w-30 with a low VI such as PP/Amsoil. For my type of driving, it's probably a good choice.

Take this two oils for example:

RL 10w-30 VI 145
Amsoil 10w-30 VI 171

Noack for both is 6%

RL is more shear stable. Could both of these oils contain little to no VII's at all? If Amsoil is using a high vis PAO/Ester, it could still have a high VI yet use little/no VII's right?

 

[jsharp]

Interesting test. Too bad we don't know what oils were used, the effects of wear metals and soot loading, fuel dilution, etc., etc.

Looks like in that particular engine 13 years ago some particular unknown brand of straight 30 weight showed better bore wear than two particular unknown 10 weight and 10W-30 weight oils.

I'd be very hesitant to extrapolate this to overall wear rates using modern oils in modern gasoline engines.

What was the recommended oil for those engines when they were being manufactured 20 + years ago? Anyone know?

 

[bruce381]

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Hey Gman maybe for winter you can PP depress the ---- out of the oil for decent winter performance send me 4 ounces and lets see if I can get the PP down some more.
bruce

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what you doing is fine I just was curious in that a small amount of PPD will bring down the pp to say -30 but a litle more say 0.5 %wt may drop it to -40 or so.
bruce

 

[bruce381]

never mind not as much effect adding extra PPD
as I thought. So adding extra will not get much improvement.

Example:
30 wt GP 1 base stock

PPD @ 0.00% PP = -6C
PPD @ 0.10% PP = -12C
PPD @ 0.25% PP = -18C
PPD @ 0.50% PP = -21C
PPD @ 1.00% PP = -24C

Thought at 1.0 % got more drop I was wrong.
brucein