ViR2 said:jdub, I wasnt talking about 50w, it just would be to heavy for normal engine, maybe suitable just for purpoise built circuit engine. I was looking at 10w-60 grade oil, and i dont see why should it be wrong. This grade is used in almost all rally races known to me, also I used to drive in Rally with compleatly built EVO VIII, and had 3 mechanics, all of them demanded only Castrol RS 10w-60 oil.
By the way, 5w-30 grade is non existant in europe (maybe such manufacturers like ELF have them, but Castrol and Mobil1 do not offer such grade).
Do u have any wear scales comparing 5w-50 or 10w-60 to some 5w-30? I would like to see more data before messing with oil
The way a multigrade works is this: For a 10W-60, the 1st number is the viscosity of the oil cold, the 2nd number is the viscosity of the oil at 100 deg C...operating temp for most motors. That's the way the oil is formulated to run...you are running a 60W oil (in this example) when your motor is at operating temp.
I know what a mechanic will tell you...ask him why. Ask him how the oil flows at 5 deg C...then go try it yourself. Put a bottle of 15W-50 in the refrigerator for a few hours and then pour it in a pan...that's how it's going to flow in your engine cold. Try the same thing with a bottle of 0W-30 and watch the difference.
I had this same exact discussion 2 weeks ago in the thread I posted above (post 10 on this thread)...look at posts 80, 83, 85, and 88. You can read it and believe whatever you wish. The problem is on engine start and getting the proper oil film thickness on the bearing journals...the lighter weight oil is far superior in this respect, especially in a tight tolerance motor. Getting proper oil flow to the journals to get the film thickness required is what's important, as is having proper flow to replace the oil on an open bearing like those used on a crank. Film thickness is not superior using an heavy weight oil.
This deserves repeating: What you will find out about oil is there is no simple answer. Wear/friction is determined by the oil used...syn vs. dino, additives, viscosity, hydrodynamic pressure, etc. All I can do is lead you to the information...it's up to you to learn it. I've done quite a bit of research, mostly prompted by JetJock (he knows more about oil than I ever will)...my conclusion is a 15W-50 (or any heavy weight grade) oil is not optimal for the 7M due to the tolerances of the engine on start.
You will have to do your own research if you want to know the truth...mechanics suffer from the same misconception as a lot of people. They were told a heavy weight oil was good...no reason as to why or based on analysis...and it keeps persisting by word of mouth. Like I said, run any oil you want...it's your engine and you can treat it anyway you see fit.
