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Old 01-27-2008, 12:28 AM   #1
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Default Plastic Intake Gaskets

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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Old 01-27-2008, 12:38 AM   #2
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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.
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Old 01-27-2008, 12:42 AM   #3
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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.
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Old 01-27-2008, 02:56 AM   #4
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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.
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Old 01-27-2008, 03:03 AM   #5
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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.
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Old 01-27-2008, 09:35 AM   #6
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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.
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Old 01-27-2008, 11:02 PM   #7
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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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Old 01-27-2008, 11:04 PM   #8
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Sad. No support whatsoever. The tiniest assembly error can kill a motor. :(
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Old 01-27-2008, 11:14 PM   #9
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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.

Quote:
Install a new design intake manifold gasket. The material used in the gasket has been changed in order to improve the sealing qualities of the gasket. When replacing the gasket, the intake manifold bolts must also be replaced and torqued to a revised specification. The new bolts will come with a pre-applied threadlocker on them.
Notice An oil leak may result if the vertical bolts are not tightened before the diagonal bolts.

Diagonal bolts may require a crows foot to tighten.

Tighten
1. Tighten the vertical lower intake manifold bolts (1) to 7 N.m (62 lb in).

2. Tighten the diagonal lower intake manifold bolts (2) to 7 N.m (62 lb in).

3. Tighten the vertical lower intake manifold bolts (1) to 13 N.m (115 lb in).

4. Tighten the diagonal lower intake manifold bolts (2) to 25 N.m (18 lb ft).
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Old 01-27-2008, 11:22 PM   #10
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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.
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