First off, if you have proper oil pressure you aren't going to have bearing to metal contact... As such things with a crankshaft, rods, and cam... all ride on a film of oil and don't have a metal to metal contact except for initial start up... in which it doesn't matter what oil you run, unless you have a pre-oiler, you run the inital split second dry, until oil pressure is built up.

And just an FYI, do you realize that motorcycles have wet clutch systems, very similar to that of an automatic transmission? Have you ever looked at the recommened oil for a motorcycle? It doesn't contain the 'friction additives' that you are talking about. Why? Because it will cause the clutch pack to slip... Doesn't seem to hurt motorcycle engines... which last time I checked, still use crankshafts, cams, and rod bearings.

It's also funny how mechanics have been using transmission fluid as a cleaning agent in engines for the last 50 years and it's never hurt anything before. Like I said, if you don't want to use it fine... but don't give other people false information about it ruining your engine or your oil viscosity. Viscosity is the 'thickness' of the oil. It's measured by determining how much fluid (oil) will flow through a given orafice in a given period of time. Now, if you add a quart of 20wt tranny fluid to 20wt motor oil, how do you figure the viscosity is going to change. This has absolutely nothing to do with the friction additives that you are now talking about, which you didn't mention in your first post... you said it will ruin the viscosity.

And as BigSwede stated:


That was pretty much the advice given above.