JHZR2
Staff member
I have yet another question regarding choosing oil viscosities. Say a vehicle calls for 10w-30 oil. OK, thats all well and good, there are a lot of good types around. But, say you know a little about oil, and want to squeeze out a few extra MPG. Would the change to 5w-30, or even 0w-30, assuming that you get a high quality oil (mobil 1) with no or high quality VIIs, make much if any difference?
I cannot imagine that the protection provided by a 0w-30 oil in an engine designed for 10w-30 could possibly be much less.
Is there a guideline for allowable spread, assuming that a high quality oil is chosen, for what is reccomended and what is used? Say my car uses a 15w-40 oil for the most part. WHat is the effect if a 0w-40 oil was used instead, all the time? Why do people talk about an oil being too light for their climate? A 5w-30 oil may be really thin at startup in 110 degree weather, but whats the problem with that? And, since engine temperature is controlled, and at steady state is more or less the same, then all that really matters is to get the top number correct for your engine design, and not have the low number be higher than the MFR's reccomended (but lower is OK).
Is my reasoning correct here?
My second, related question is regarding oil weight specs, and engine design. What is the important thing, the ability for oil to flow through the engine, or the ability to have a certain viscosity? There are all sorts of numbers provided on the spec sheets, but I am not very knowledgable as to what are really important to the engine design and oil specification. At low temperatures, is it more important to have something that pumps well, or is it more important to have something with a certain viscosity (both things are related, but synth oils, for example, pump well in the cold, but have essentially the same viscosity as a dino oil). At high temperatures, I guess most specs are the same, or unimportant for the most part (assuming your engine is healthy and not too hot), except shear stability. so then the viscosity chosen by the MFR. is based upon bearing clearances almost entirely, correct?
I am sure these are relatively simple questions, but Im trying to learn as much as possible for my own ood, and thank you for your help... this site is great!
JMH