Quote:
Originally Posted by EricSilver
I had a tech who specified 20-50 for high-revving engines, but I did not follow his logic. (The faster a machine spins, the less I would want to inhibit its performance with a heavy oil.)
I think the kindest thing I can do to my engine is to relieve as much of the burden placed upon it as possible. With 15W oil, it was under visible strain, i.e. vibration, sound, and a jittery oil pressure needle -- as if the 15W had a harder time flowing through the filter. With lower oil weight, everything settles down.
Oils I have used ranged from 10W-30 to 15W-40. The ideal compromise was probably Rotella 5W-40 synthetic (but it still made me uncomfortable when driving in hot weather).
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Those broad spectrum oils are not near as robust/long lived as those w/ a lesser spread even with a synthetic. The friction modifiers/viscosity improves required to achieve the spread make the polymers more likely to shear.
I have never experienced any of the aforementioned symptoms you describe when running heavy weight oils. All of my, and my customers M116/117's/103's/110's/119's all run 20/50 hear in the summer (my personal cars run 20/50 year round due to my particular driving style) and 15/40 in the winter months.
Jonathan