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.

 

I would break it in for at least 5k miles before using Syn oil.

Chris
'88 F350 XLT Lariat CC DRW/7.5l/C6/4.10
'93 Mustang LX 5.0l/T-5/3.55's/Flo's/pulleys/K&N
Nissan p/u (DC commuter)
Volvo 940

 

Sometimes synthetic oil will leak out when conventional oil wont. Its just "slipperyer". Waiting until 5K miles is good advise. A new motor should be broken in on petrolium oil, then switch.

Nathan

 

Thanks guys. I just wish I had a little more information about using synthetics with older designed engines.

 

check with Jasper and see if the warranty will be voided if you use synthetic's. also make sure the cam manufacture can use the oil. alot of cams can"t use this oil it will destroy the cam.

 

Warrenty says to follow guidelines in original owners manual. The original owners manual does not prohibit the use of synthetics.

Thanks guys! The more that I think about it the, more I think that I will try synthetic oil again.

 

The early design of Mobile One synthetic's (and other's) had an additive put in to swell up the seals a little to help keep from leaking on high mileage engines. By doing so, it actually detoriated the seals faster causinig leaks. From what I understand that additive has been dropped long ago and today's synthetics are far superior than the one's on the market 20 years ago.


Xaviar

 

The "wait to use synthetics till X miles" is an old wives tale. Many NEW cars (read expensive) start from the factory with synthetics. Corvette, MB, Porsche just to name a few. Go ahead and use it at the first oil change if you'd like. Your rings will seat, your cam will not magically be destroyed and you will have a little bit more piece of mind during the hot summer months.

 

I have a 1970 351W in my '64.. speedshop rebuild.. not to wild.. but my builder suggested I break it in with conventional 10w30 or 30 weight, then switch to Mobile I... I ran the conventional oil (oil changed right after cam breakin) for 2000 miles before I switched to 20w50 Mobile I.. (again the heavier weight was the builders recommendation due to the way the engine is set up).. I now have about 4000 miles on the engine and time to change again.. no problems to report...

Bill in Mobile
'64 F100 Shortbox ('70 351W/'76 C4)

 

Thanks guys! This is really helping me make my decision. I thing I'll go to synth at my next oil change.