67mustang302

False(sort of). Heavier oil protects better. IF the engine can NOT use it, that doesn't mean heavier oil doesn't protect better, just that it won't work in that engine. Engines designed with tighter clearances are done so for mileage and emissions so they can "get away with" running thinner oils.

Look at how higher performing race engines are built, looser tolerance, heavier oils. And some of them do run gear oil(in terms of weight). Most of the nitro burning engines run something like a straight 70wt.

Keep in mind that viscosity does NOT mean how easily oil pours when cold, that's just how they measure viscosity indirectly since it relates in most cases somewhat linearly to "pourability". Viscosity is actually measuring the oils ability to resist sheer in a given thermal range at a molecular level. High viscosity oils are less prone under shearing forces at temperature to separate and generate air pockets. Fuel in the oil from blow-by also lowers viscosity by thinning the oil since it acts as a solvent.

Basically, if you plan on running hard you're best bet in terms of protection is to run the heaviest oil that the clearances will allow. Engines that are spec'd for 30wt can run 50, if it's spec'd for 20wt then 40wt is about the highest you'd want to go. Some of the newer smaller engines run 0-15 oils, so 30wt is about the heaviest you'd want to go. Also good synthetics have better pumpability than mineral oils.

mustangGT86_05

right I understand your point, thats why I said not exactly true. Higher performing engines need the thicker oil so that the oil doesnt give way under the extreme conditions. But I made the point so that people who don't race or whatever don't end up convincing themselves they are helping their engine with a much thicker oil than needed. Theres 2 sides to everything, unfortunately lol