Synthetic oil dries out seals.

AZjeff

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High Mileage versions of engine oils have extra seal restorative products in them that can actually restore a seal and stop it from leaking if it has just dried out from too much use of a synthetic engine oil. Some synthetic engine oils will dry out the RMS and start it leaking.

This quote came from a respected long time member on another automotive forum I frequent. No use trying to clarify since it would result in an ugly dog pile for insinuating the esteemed member wrong. Some myths just won't die.
 
Such as that gets old. The same bad information just gets regurgitated over and over. Synthetic oil drying out seals and causing leaks is the big myth, but there's also the myth there of high mileage oil stopping a seal leak. The additional amount of ester-based seal conditioner in HM oil is quite small. It's just enough to keep a seal pliable a little longer. It's not enough to reverse the condition of an already dry rotted seal, much less stop a leak. It may help a little bit, slow the leak a little bit, but highly unlikely to stop a leak or repair the seal completely.

I blame hyperbolic marketing for a lot of these myths.
 
He's entilitled to his opinion. I fail to see any reason to post his quotation.

He doesn't present it as an opinion but as fact, no IMO present. People less versed in oil and what it does and doesn't do will believe his incorrect assertion. Can't recall anyone saying synthetic dries out seals before.
 
we have a nationally ranked/known Auto/Diesel/Motorsports college here in town... one of the instructors, who the local TV station and Newspapers have on call as an "Auto Expert" is still teaching young mechanics that not only can't you mix Conventional/Synthetic oil, but that if you put synthetic in, you can never put Conventional in it again...

few years back i was working retail with one of the students, who blew up the 5.3 in his Silverado, he got mad at the Chevy dealer back in his hometown for putting synthetic oil in his new engine..."cuz now I can't use regular oil any more!"

never mind that ( now i could be wrong, but i'm fairly certain...) chevy specs synthetic oil... and he had it done at the Chevy Dealer...
 
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