quote:
Originally posted by Titan:
Oil is the "blood" of an engine. Viscosity is like the hematocrit. Too thin, and the heart has to be able to pump a little more per minute to keep up with the tissue requirements (but, that's not hard to do when the resistance is decreased with thinner fluid to pump). Too thick, and the heart has to pump HARDER to overcome the viscosity-induced drag, which takes more energy input. PLUS, the smallest capillaries may be underperfused, and sludged. Yep, that is the term used...it isn't sludge like oil sludge, but, it is areas of decreased/no flow. Athletes, blood doping, and the problems it creates are good examples of what can go wrong with having fluids too thick.
Below operating temps, oil is too viscous. This slow-flowing, too-thick oil is what is causing the increased wear at startup, and for the first 10-15 minutes of operation. TOO thick is obviously bad. What constitutes too thick, depends upon other things besides temperature. If you have an older engine with a bit of crud built up in some of the oil passageways, your engine might run cooler/better with THINNER oil, because thinner oil can squeeze through the narrow passageway better than thick oil (we use that information in medicine to provide better blood flow past narrowed arteries...you want the blood less viscous in order to perfuse the areas past the narrowing. And, no, this is not related to "blood thinners"...I wish EVERYONE would quit using that incorrect terminology...people are not on "blood thinners", they are on anticoagulants. Completely different subject.)
Anyway, I think there are very good reasons to steer away from using oil that might be too thick: and remember, they are ALL too thick at startup.