View Full Version : mechanic recommends oil additive

06-26-05, 08:52 AM
Hi, I recently bought a '99 Seville with rather high mileage and it leaks oil from the main (lower) seal. Cadillac dealership mechanic said it would cost several thousand to replace gaskets, but that an engine additive that expands the gaskets would bring that leak down to almost nothing. He says it does not do damage in any way.
Any experience or thoughts out there on this recommendation? thanks.

06-26-05, 11:50 AM
I remember some stuff like that that swelled up seals and reduced leaks for awhile, but it broke the material down in the process and eventually the seal failed altogether and leaked as though there were no seal in it at all. It was mostly used as a ploy to sell a car. And by the way 130K miles is nothing for a N*. With the right care they are a 250K engine.

06-26-05, 12:20 PM
Generally speaking, I put most "repairs in a bottle" in the snake oil category though I admit I know nothing about this stuff. The old "If it sounds to good to be true, it usually is" adage usually applies.

06-27-05, 11:45 AM
thanks for the posts, guys;

normally I would have just dismissed this advice in a similar way, except for the fact that it came from a very honest, knowledgeable, candid and experienced mechanic, one that I trust more-or-less implicitly on most of my car matters.

My Seville did not leak at all until I put a can of engine cleaner stuff, and suddenly it's leaking like crazy. maybe someone before me HAD used some of this gasket expander stuff, and now MY additive flushed it away and disintegrated the seals or something.
I just don't quite get it; it's fine one day, the next day it's leaking lots of oil.

by the way, the source of the leak (lower gasket) has been confirmed by three seperate sources, two of whom I paid for the diagnosis.

06-27-05, 12:57 PM
There are some additives out there that cause some gasket materials to swell up a bit, thereby closing some small gaps, but those additives tend to degrade the gasket material and a major gasket breach can be caused by them some time down the road. There are no additives I've ever heard of that coagulate or build a dam across any gasket gaps in an oil system, such as what the Bar's Leaks powder does in cooling systems. Anything that did that sort of thing would probably cause some other major problem. Whatever additive your trusted mechanic friend likes probably contains a higher concentration of the gasket swelling compounds and thus helps to seal larger leaks a little better than other brands. At the same time, though, if it swells the gaskets more, it will probably also degrade them faster. It's possible that the combination of a previous use of gasket swelling chemicals weakened a section of gasket, then the cleaner or whatever you put in there weakened it further or somehow otherwise accelerated the failure. If a large breach has occurred in the gasket, no additives or chemicals will fix it, no matter how much gasket swelling capacity they have. If the gasket is blown, there is nothing to do but fix it. You can try the additive because it might be a cheap fix, but my guess is it will only slightly, maybe not even noticeably, slow it down and you'll wind up fixing the gasket. It's a crappy situation.

06-28-05, 10:41 AM
Thanks, mcowden; you stated exactly what my suspicion is. especially the part about the "clean-out" additive that I added causing a flushing out some previously-added gasket swelling condition.

I guess I will just have to drive it this way for quite a while until I can save up the two grand it costs to fix it properly.

by the way, you mentioned "blown gasket"; what exactly is that? what happens when an engine experiences a blown gasket?

Thoughts, anyone??

06-28-05, 11:22 PM
Blown gasket is simply mechanic's slang for a gasket failure. It leaks badly.