When I first picked up my T2 firebird Ed Bilmar told me to run 15w-50 and only that. GM of course says to run 5w-30. Well long story short, I listend to Ed and the motor was fine. I did a freshen-up on my motor this past winter and am wondering should I run 15w-50 after break in, use 10w-30 or go with 5w-30? The car is driven on the street from time to time but spends more of its life on the road course. Currently is leaks a little to so I hope that going with a heavier oil will cure that

What dictates what oil should be used aside from bearing clearances and weather? Since my car was build with facotry clearances and I run the car only in summer shouldn't it be save to goto atleast a 10w?

I know this has been awnsered before on "what oil to use" but I never caught the why and how to determine part.. Thanks!

 

5W30 is probably your best bet. If you live anywhere other than places where it constantly gets above 95 degrees F then you'll want to use 5W30. For people who live in hot climates, go ahead and try 10W30, however I would not use 10W40 or higher unless you have a supercharger or run the **** out of your car then 15w50 makes sence because more stress on the engine needs more protection

 

Does your idea of beating the **** out of it count running road course? I think it does My question is why do you come the that conclusion. I assume that running a 15W will cause more wear when the oil is cold but what about general operating tempatures?

 

Oil is a more complicated subject than it seems. I run 15W-50 because with a blower and N2O, it's hell on bearings, and the thicker oil at high temps will hopefully provide a better cushion. OTOH, I do not run my car in cold temps, I always fully warm it up before putting under much load, etc. In addition, I have my motor set up a little "loose", so the higher pressure with the thicker oil is a plus, also to protect the bearings. The few hp lost to running a thicker oil isn't of much importance with my setup, the protection is.

If you are a more typical user, 10W-30 is the way to go except in prologed, very cold weather where a 5W or even a 0W oil may be indicated. In persistent very hot weather, an oil like the 15W-50 may be a good choice. But in most of the continental US, stick with 10W-30 for all around use.

Rich Krause

 

If you truly honestly want to figure out which of those two viscosities of oil works best for your engine, do an oil analysis on two intervals with 15w50 and then two intervals with 5w30, and compare the numbers. To be honest, you more than likely will not need 15w50, it's simply too thick for the clearances in these engines. The 5w30 will flow better, run lower oil temps and will show lower engine wear numbers in oil analysis.