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 wifes 99 Expy since it had 500 miles on it with out any problems. However, I started using Mobil 1 in my bronce 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.

 

Synthetic oil will flow to leaking more easily than regular motor oil. When I install a new motor in my 85 Bronco, I had no problems with leaking when using synthetic oil.

 

Thanks for the reply Winkelhawk. Do you still have the 85 Bronco? How many miles on the new engine? Are you still using the Synthetic oil?