based on what ive heard, 10w-40 was 10w-40 whether synth or dino, that was the main reason i never understood why it was believed you cant switch back.
it would seem that the thickness of the coating on the parts would only matter at start up, when the engine is "dry" because a thicker coat would decrease initial wear maybe-but if you can have a thinner coat on the parts yet still have the same friction coefficient, then it shouldnt matter i think. but thats off on a tangent-
anyway pertaining to the question-could it be that early synths had additives that reacted to the additives in the dino oil that destroyed seals? actually that dont make sense because then it shouldnt be compatible at all, dino to synth wouldnt be possible either.
just throwin stuff out there. i think it could possibly even be that some ppl took their vehicles to the dealer, took a chance and tryed synth-and didnt notice a difference that was worth the extra money. instead of switching back and saving money, they were told they couldnt switch back. cars come with synth now (most do i believe) so you have no choice but to use the more expensive synth. no more $15 oil changes. just another idea....
obviously u can switch back and forth with no problem according to the oil companies, so who the hell started this myth lol
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