i know your supposed to change your oil evry 3k-5k miles, but im thinking of putting synthetic oil in my next change. whats the general life of the synthetic oil? and any one use this kind oil? i heard its supposed to be really good heat resistant wise.

 

An 89 should have an oil with zinc as an ingredient which synthetic does not. Zinc protects the valve train and cam. For years oil designed for a diesel had the zinc. Most now do not! If it were my car, I would use the 15/40 Chevron Delo, unless you live in an extreemly cold winter area,with The GM additive E.O.S. ( eng.oil supplement) which provides the zinc. Synthetic as well as conventionaloils can go 7500 miles with no issue.

 

oh well i actually sold my 89 fleetwood, i have a 94 fleetwood now. [really wish i wouldnt of put 89' as my user name] and i live in the blazing heat of florida. but you say 7500 mile huh? one guy told me 15k miles, i didnt really believe him.

 

When our fathers had their cars serviced, it was done either at 3000 or 5000 mile intervals, not because the oil was worn out but because the oil was contaminated by raw gas dripping into the crankcase and inefficiant crank case breather systems which caused acids to form. New cars that are fuel injected do not dilute the oil with gas, new breather systems and hotter running engines lessen the formation of harmful acids and moistureso the oil lasts longer. When I was a teenager in the 60's I sold recycled oil every day that worked just fine. Just my opinion after 30 plus years as a service manager/advisor with many new car dealerships. And add your newest car to your profile signature as my cars are displayed.