LetThePoniesRunFree

Listen my friend. I don't care what anyone else says about this synthetic vs petroleum oil on high mileage vehicles.[8D] A high qualitysynthetic oil will NEVER hurt your engine no matter how many miles it has on it. Synthetic motor oils have smaller molecules than your standard petroleum based motor oils. That is how a synthetic motor oil benefits your engine. It gets to places petroleum products cant get to. But, you have to keep in mind that if you have any sort of seepage through a gasket surface when using a petroleum based oil, that seepage will be greatly increased if you use a synthetic oil only because of the nature and design of the synthetic oil. No oil, synthetic or petroleum "boils" off under normal driving conditions. If you have blow by via the rings, you will notice more smoke out of the exhaustwitha petroleum product. Here again is the nature of a synthetic to have the ability to "seep" through a specific clearance that is smaller than what a normal oil can do.

CobraStangGT16

I have a 99 GT as well, and I bought my car from some guy who disappears after I bought the car. I don't know what kind of oil he used, and I have no idea when the last time was when he changed his oil. So I'm doing it tomorrow. I have 98k miles on my car, and I bought 6 quarts of Mobil 1 synthetic 5w-20 and a motorcraft filter.

Supposedly, if he didn't use synth. oil, this still wont do damage to my car if I change to synth. tomorrow?

Thanks. I had some issues with different opinons on this subject.

LetThePoniesRunFree

No man. Synthetics CAN NOT HURT your engine. Can you imagine how many law suits there would be if someone could prove synthetic oils hurt you engine? Come on now. The ONLY down fall of synthetics is they will find every leaky gasket on your engine.

CobraStangGT16

Well thats not good!!! I have a motor with almost 100k! Theres bound to be a leaky gasket somewhere in thar! Where are the usual spots to look for? Rear main seal?

Yeah I knew this was coming though. Synthetic oil is MUCH more viscous than regular oil.

*viscous- The resistence of a fluid to deform under shear stress.

LetThePoniesRunFree

You guys are really blowing this way out of proportion. If you don't spot the drive you park in now, you probably won't spot it after using a synthetic.

CobraStangGT16

OK, then...nothing to worry about!

Thanks!

SmallFeesh

Royal Purple Syn. all the way!