5-40 Oil, I know it is a no-no....

[Chucks Stude]

Is anyone using the new Rotella 5-40 synthetic? It is not a diesel oil, but looks like something that might be good for cars that aren't run every day. Thoughts?

[StudeRich]

Since you KNOW too light (thin) a viscosity oil is a No-no in a American made Engine, then why even consider it? Just DON"T!

Update: (Thanks Mike V V) More CORRECTLY, not in an older school engine with looser tolerances.
Lol! I just could not think of a new car WITH an American made Engine!

[Mike Van Veghten]

Yep...only if the engine's rebuilt with tighter bearing clearances and balanced properly.

Has nothing to do with....American...engines..! Most of todays...American engines are designed and built with slightly tighter clearances and can (see owners manuals !) run thinner oils.

The NASCAR guys...um..."race" engines run (or used to) 5-xx and 10-xx weight oils during qualifing. While that may only be 3 or 4 laps...it IS at nearly 200mph on some tracks..!
The same thing is sometimes done in drag racing also.

I in fact had my crank ground with more of a "factory" clearance rather than a race clearance...even though this engine will see more drag racing thAn it will street driving.

Mike

P.s. - Chuck...na..on a, stock, long since it's last rebuild Stude engine...run the heavier oil.
I run Castrol GTX, 20/50 in my daily driver 259 Lark.

[Chucks Stude]

I am running 15-40 for the winter, and 20-50 for summer since it is so hot here. I was just thinking that for winter, and infrequent starts during the winter, that it might run thru the passages better when it is cold. Agree with you all on the thicker stuff, especially during the summer.

[Bud]

I would think that the use of a lighter synthetic oil in an engine that is in good shape shouldn't be a problem. The 5W-40 synthetic oil can be used place of the older 15W-40 in diesel engines with no ill effects as the oil will remain at SAE 40 when it's hot and will flow better when it's cold providing faster lubrication at startup in cold weather. All I can say is to try it and watch the oil pressure when your engine heats up. I've been using Mobil 1 15W-50 in my Avanti for a couple of years and the oil pressure stays higher when the engine is hot vs. Castrol 20-50 regular oil. Bud