Originally Posted by IcemanV8
Not only should you never mix them, you should never use synthetic oil in a car that has been running normal oil for a good amount of time. It will break up build up from the old oil and that will go through your engine, causing some damage. You don't want old chunks floating through your engine.
Sure, some people have done it, heard of someone who has done it, etc., and didn't have any problems, but then there are the ones that have done it, heard of someone who has done it, etc., that DID have problems. On a brand new, clean engine, I would want to run synthetic. Talk about keeping your engine clean, but other than that, stick with what's been in it.
So you have never done the Seafoam thing in your car?
That is exactly what that does; (Break all the crap loose) It makes a major difference...or at least it did to me...that was the dirtiest oil I've ever seen, that came out after the Seafoam oil change/seafoam intake/ seafoam gas treatment job I did. Car felt new...
I use synthetic on everything; it makes a large difference in gas milage, 3-4 mpg, and the engine feels smoother.
I changed my 63 bird from quaker state to castrol, years ago, and it made a major difference too, but I had the valve covers off, and cleaned all the solidifies paraffin out first; THAT would have probably killed the engine, for sure, if I hadn't got that out...
I did a post in a thread about quaker state oil; search for it...You sound a lot like my Dad's mech did, before I showed him all the crap out of my engine...
Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.
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