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

[modularv8]

I have this SAE paper and the authors give no information about the formulation/properties of the oil, except for the grades. Very often researchers conduct lab/engine tests oils that are not fully formulated oils like you find on the market. Furthermore, they commonly do tests of oils that have considerably different formulations from each other; giving day and night results from each other that are the results of the additives. We don't know the straight 30 is fully formulated while the other 2 are not. The results of many of these SAE published studies can not be generalized because the conditions of the tests conducted are not representative of real world performance of engines or lubricants, the authors design an experiment only to determine some preset hypothesis of their study. Alot of studies do accurately represent real world outcomes.

The chart posted in this study is one of many charts of this study. The goal of the researchers (Mercedes) was determine the effects extended oil drain intervals. These kind of studies are usually done in extreme conditions with different oil additive chemistries and formulations to determine the effects of aged oil performance differences. Having said that, a fully formulated mineral multigrade has much better wear performance than a straight grade because of its better flow properties over a temperature range and the load bearing capacity of VIIs polymers. Some synthetic 10w30 formulations are essentially straight 30 wts.

 

[friendly_jacek]

Thanks for commenting on this paper. I didn't read the whole study, but the type of oils should be fully disclosed in the methods.

As for multigrade oils generating less wear that it certainly true for very low temps. But, the above graph doesn't deal with the low extremes in temps and the 20-80C results are very interesting to say the least.

The wear effect of VII is limited to bearing wear only (IIRC) and shouldn't be relevant to cylinder wear.

 

[modularv8]

Originally Posted By: friendly_jacek

The wear effect of VII is limited to bearing wear only (IIRC) and shouldn't be relevant to cylinder wear.


That is correct, only bearings. I think what may be happening here, is this test was done to see the effects of oil aging on viscosity modifiers. Alot of the studies I have seen, age the oil under extreme conditions (simulated aging with high temps) to the point of extreme degradation/failure. The multigrade oil will come out weaker than a straight grade because the viscosity modifiers have essentially been destroyed (during the aging process) leaving behind a weaker lubricant to do its work compared to a straight weight. This is one of the reasons straight weights are recommended in air cooled lawn equipment and most aviation engines (why it was posted in an aviation forum), but not in modern automotive engines.

 

[gfh77665]

Good thread here. I have had good luck mixing in 30 and 40 wt. with 5-30 and 10-30, and even running some of the 30 and 40 straight, albeit in generally hot SE TX.