I have a 1994 Z28 stock with 70k miles. I want to use mobil 1 synthetic. The car calls for 5W30 but i hear alot of people using 10W30, what is the best to use?

 

During the warm months up here in Michigan I use the 10 weight because it doesn't thin out as easy with the heat. In the colder months I go back to 5 weight because you don't want the oil real thick with the cold weather.

 

I started useing the 15/50 at 80thousand miles I live in Fla.

 

If you're using a synthetic then 5w30 and 10w30 would both offer the same performance, both will be just as thick when hot, it's just that the 5w will flow better on startup. A dino 5w30 will thin out quickly and become 5w20 though, while a dino 10w30 remains a 10w30 much longer. A good 5w30 synthetic won't thin out though, so it'll offer just as good high temperature protection as 10w30 synthetics would.

15w50 is far too thick, even in the hottest weather. You're just robbing yourself of power and you're going to have higher oil temps with the engine working so hard to pump the thicker oil. Go no higher than 10w40 in these engines. 15w50s are for loose clearance engines and all out race vehicles, not for the average street car.

 

I like 10w30 year round. My car is garaged at night during winter.

John

 

I tryed 10w30 and my oil pressure was way to low at an idle! Switched to 15w50 and oil pressure is alot better at idle! (both oils carried really good pressure under acceleration)

 

That's because the thicker oil isn't flowing as well. It's a band aid fix, sort of like adding STP oil treatment in order to boost your oil pressure. You're not fixing the problem at hand, just masking it.

 

This gets discussed a lot. You might want to do a search.

Rich Krause

 

15-50 the guy at Crane Cams reccomends using this wieght with the roller rockers. Can't say they don't know what's up.

 

Why not? Do they have oil analysis results which prove it works better? Probably not. A lot of old school mechanics recommend super thick oils, do you think they studied lubrication? No, they simply are hanging onto old beliefs.

 

Hmm. I was thinking about going to Mobil 1 10w30 synthetic once I finish out the last batch of my break in dyno oil. I currently using mobil 1 5w30. Would it be a good choice to step up to 10w30 for the summer or should I just stick with the 5w30?

 

They guy at Crane explained to me that it'll help pump up the lifters better, cushion the internals when accelerated hard, that and I know it's a good idea to run the 15-50 when usin n20 again for the cushioning effect that it has. Maybe they have run tests, I don't know, I just trust these guys at Crane. I wouldn't use it if I lived where it was cold during the winters, but with a good filter you shouldn't have problems. That's what I ran and I never had problems, my 2 cents.