I just put a rebuilt (Jasper) 302 in my 91 Bronco and have been considering using synthetic oil. I've been using Mobil 1 in my wife's 99 Expy since it had 500 miles on it with out any problems. However, I started using Mobil 1 in my bronco when it had 40K on it and at the time I replaced the Engine, it was leaking oil out of every seal that the oil touched. Did I wait to long to start using synthetics? Are the older engines just not very compatible with synthetics? Will the seals in the Rebuild be more compatible?

I do know that I got 1.5 Mpg better with the Synth than I did with the Conventional and would like to consider using it again. Any inputs would be helpfull.

 

On a brand new engine i would definitely use synthetic oil.(just stick with it)
I'm not too sure about the old engine with the oil leaks.But i've heard that you should not use synthetic oil on an engine that initially used petroleum based oil.
I hope this helps.
Jerry D
http://hometown.aol.com/dvldog458/myhomepage/auto.html