Quote:
Originally Posted by Steve Tinker
Why would you use 20W-50 in your engine even in elevated air temperatures - thicker is not always better.
The secret to good lubrication and cooling is oil flow, not viscosity. If oil thickness ( xxW-50) was the secret recipe for hot climates, why wouldn't you put in strait W-50 oil?
The oil flow to the bearings is (generally) dictated by the coolant temperature - lowering the coolant is possibly the best thing you can do for your oil.
In the old days, if you had 10 psi per 1000 rpm @ hot running temperture (never mind the viscosity), you were good to go....
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I am not an oil expert but my understanding (which could be wrong) is that at high temps lower viscosity oils can thin and/or become aerated to an extent that will reduce the oil's ability to adequately lubricate the moving parts. Thus, it has been common practice to use higher viscosity oil in warmer climates in an attempt to mitigate these concerns.
And yes, some racers back in the day have been known to use single viscosity 40 or 50 weight but these days almost everyone simply runs a temperature appropriate multi-grade oil.
Last, its almost impossible to separate facts from marketing hype these days. Even if a straight 30 weight would work fine for many people (like it did for many of us, our parents, or our grandparents), the oil companies have marketed multi-viscosity oils so heavily that single viscosity oils are nearly obsolete regardless of the reasons/benefits/concerns.