Originally Posted By: Solarent
What Mr. Ballentine fails to mention in his article is the role that new additive combinations are playing in controlling wear in thinner oils. In terms of viscosity to maintain the proper oil pressure, CATERHAM can probably speak to this better than I can, but as far as I am concerned the proper viscosity oil for your engine has more to do with engine design than anything else. Thicker Oil - depending on the engine design is not going to automatically give you better protection. Viscosity has much less to do with protecting wear now when you factor in bearing material and design, additives and other factors of the elastohydrodynamic regime.
...is going to make the consumer market a bit of a mess I think, but interesting because basically what the API and SAE are saying is that using thinner oils in older engines to obtain fuel economy improvements may not be good for those engines.
Solarent i'm not one to clamor for evidence as an entry ticket to discussion, i know in certain circumstances we have to make decisions without clear evidence and in those situations i want to remain open-minded to counter positions and evidence. I think for some cars and driving styles, a 1-step increase in viscosity will provide better protection unless the 20 wt add pack is vastly superior, but that's not so if you compare within brands. I see your point about better materials but thats another issue and also very difficult to prove.
Originally Posted By: CATERHAM
...Secondly, the assumption that more "protection" will be provided is often second guessing the oil grade recommendations of the manufacturer. Technically a heavier oil doesn't provide more "protection" but rather a greater viscosity reserve in the event of high oil temp's. The heavier oil is totally counter-productive if the higher oils temp's required to justify it's use does not occur.
It worth reminding all that when a 20wt oil is specified a very large viscosity reserve is still present to deal with higher than normal oil temperatures. Exceeding these viscosity reserves virtually always entails engine abuse such as exceeding the OCI, low oil level, using a low quality (non API) oil and/or exceeding the load carrying/towing capacity of the vehicle, something anal BITOG members would never do.
Caterham i respect you for the HTHS thread and your other work but i disagree because towing a load that is a bit under the rated spec will also increase stress and heat in a very large way compared to normal driving. Also racing and high torque/hp applications that many bitog members also drive.
you know the jump from 20 to 30 is very small compared to 30 to 40 (a 40% increase in visc vs 20 to 30 about 10%). So i would say the temp increase in 30 vs. 20 is also small compared to other jumps, but like you said, "does it justify it's use?" I think it would in certain apps but i have no proof.
This seems to be a matter of trusting the manufacturers with their billions in resources and engineering. Yes, it may sound presumptuous or foolish to question them but there are other business and political considerations in their recommendations. It's not NASA where they need to have multiple failsafes and way conservative numbers for the high degree of danger. So yes, in typical bitog fashion we are dissecting fine points here. gotta love it