These are pictures of the Felpro LIM gaskets on a 3400 engine that belongs to my daughter-in-law. They were installed less than 2 years ago when I replaced the head gaskets. Dex was not an issue here, as Prestone "all makes/all models" has been in the van since before the head gaskets went. I'll try to get some better pictures later. You have to look closely, but the plastic has degraded around all of the ports, in particular the coolant ports. She says that the engine has not overheated. Started out doing this job because of an external coolant leak, that apparently recently started leaking internally as well.
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I'm using the GM gasket kit that is listed in a TSB, this time. It includes the new gasket (still plastic), and new LIM bolts. There is also a revised torque sequence. I'm hoping that these will last longer, as it is a PITA to work on!

This is the foamy oil left behind.
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Ahh yes..... 60* LIM gaskets are NOT fun. My 2 3100'* I had were a absolute pain in the *** to rip apart.

Why I decided to stay with the 3800s.

Could be a gasket issue. :?

Could be a design issue :?

Could be an installation issue :?

Whenever I seal engine gaskets around coolant ports, I always use a smear of RTV even when the sealing surfaces are rubber. Not sure if that would have helped in your case but I never have leaks.

I know the manufacturer uses some kind of clear sealer on all metal gasketed surfaces. I have used the spray on type for intake ports on V8 engines but prefer using an RTV smear around coolant ports cause it seals and it'* almost non-existent if you ever have to remove the parts in the future making clean up simple.

Yeah, just recently had our friend'* 3100 crap out (previous owners of the av) in a 98 lumina. they said they smelled coolant....so i opened the hood...poked around...and smelled right around the LIM, gee, whattya know, coolant. the dex had been swapped out at about 75k, it now has 125k. i dont know its current status, but i know it isn't good.

That motor has a totally different set of problems than ours. Mostly in design. The new designed Nylon gaskets won't solve the issue permanently either. They roll the sealing material around the port edges.

The problem is in gasket retention and motor design.

They certainly do, including head gasket failures. I was hoping that the new gasket material would be similar to the one for the 3800s. No such luck. With the layout of things...having to remove the coil packs which are tucked well back under the cowl and over the rear valve cover making it tough to remove the bottom nuts, valve covers attached to the LIM, which have to be removed anyway, as the rockers have to be loosened to remove the push rods, because the gasket is under them, and other issues, this is not a job I want to do again soon. Bill Buttermore described it perfectly when I was doing the head gasket last time....it'* like working in the toe end of a boot!

I was wondering, as SilverBullet described, if putting RTV around the ports will help.

Some better pictures of the failed gaskets.
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and a closer view of the area around the coolant ports. These were on the intake side of the engine.
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This is the redesigned GM gasket. The only difference that I can see by just looking at them is the addition of 2 metal inserts near the bolt holes on each end. Maybe a little more material around the coolant passages?
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Sad. No support whatsoever. The tiniest assembly error can kill a motor. :(

Yeah...not much there...why I was hoping for the aluminum framed gaskets for better support. This is part of the TSB regarding it. What the new material may be for better sealing, I do not know.

It'* more of a rubber than a silicone. The difference isn't in the material though. It'* in the way it wraps around to protect the nylon.