Greetings,

Ok, so I have one of those dreaded lower intake manifold gaskets made of plastic. My car is doing a couple of things that shows me there maaaay be something wrong with the gasket.

I will ask, what are all of the symptoms of a leaking LIM gasket?

Here is what I am seeing and experiencing. It's been going on for a while.

I noticed below the plastic air plenum on the metallic manifold (I don't actually know what I am looking at), there are pockets that are filled with oil. I drained them and see them veeeeerrrrrry slowly starting to fill back up (days later). Perhaps this is the valve cover gasket?

I see a little lack of coolant. Not a lot. Once the car is running and warmed, the coolant appears to be full. I have hardly ever had to top it up. When the car is cold, I can open the rad cap and not see fluid.

The car stumbles a little bit when idling. We're talking between 800-850 rpm for half a second every 4 of 5 seconds or so. Easy to see on the tach but not a major hesitation.

I'm wrist deep into my engine and I don't mind getting up to my elbows as long as I can get back out. She's my daily driver and I don't want her on blocks for days on end.

 

If you are concerned and not afraid to take the top half apart, just go ahead and do that and replace all the gaskets as you go back up. Also clean the parts you remove completely.

FELPRO makes an aluminum LIM gasket that should fix your problems. The valve cover gaskets are also pretty prone to going.

 

Sounds good! Are there other things I should be doing during this? Does there happen to be a walk-through of replacing the LIM gasket?

 

Haynes Manuals should help you a ton!

Articles - NAIOA

^^^ There is a decent walkthrough.

Just replace EVERYthing you can that is cheap to replace. Good time to do your plugs/wires/coolant elbows/gaskets/ etc.

 

I've used a radiator pressure tester and I have been able to find areas where coolant will bubble out (usually around the top of the LIM, near the top of the valve cover gaskets).

I agree with Chibi, if you think they went bad, it may be worth popping it apart and doing the job now. It's REAL easy. The only thing I used a shop book for my first time around was torque specs. Use Fel Pro aluminum LIM gaskets, Sadly, you still need to use the nylon UIM gasket. But these are not as prone to failure.

This would also be a good time to consider new plugs/wires if you need them and perhaps a refresh on valve cover gaskets.

As Chibi said, clean the parts off. You'll thank us later (re-assembly is just better with clean parts).

 

Thanks very much. Say, would you use the fel-pro aluminum gaskets or the GM OEM for the LIM? Also, do you happen to know the part numbers?

 

Definitely the metal ones. I don't have the part number on hand.

 

I bought mine from RockAuto.com and I used the FelPro ones (I did have to e-mail them and ask if it was the aluminum gasket, as I believe the description at the time stated something like "New solid carrier" or something a little ambiguous).

I believe there might be another company doing the aluminum LIM gaskets, but I just with Fel Pro. They are a good brand.

Whatever you do, just stay away from the nylon LIM gaskets. You will still need a nylon UIM gasket, but that's no big deal. And I think Dorman is about the only company to sell it.

OH and the Dorman UIM kit comes with stuff you may or may not need (like a throttle body gasket, I pulled my UIM off with T-body attached and saved the gasket for another time). BUT it also includes a modified narrow stove pipe. From what I've read, the factory stove pipe can cause some damage over time due to heat on the UIM. The narow pipe is to help prevent that damage (stuff I read on the Bonneville forums). I know when I modded my Monte with a port matched LIM last spring, I swapped the stove pipe over to the narrow one.

 

FelPro gaskets are GM's OEM version. GM doesn't make their own gaskets, they get them produced by another company then put their logo on it.

Originally it was FelPro that made them, then when GM first switched to metal ones in 06 Mr. Gasket made them, now they're back to FelPro.

 

Man, I guess buying up here is harder than it looks. I've got one hell of a time getting some straight answers from the suppliers; HOWEVER, I have had one dude tell me some descriptions.

Felpro - Permadry
or
Felpro 2nd Design; w/Rubber-plastic end seals w Locating pins

He tells me that both were a 2nd design but cannot tell me if the permadry or the '2nd design' are aluminum. He wouldn't give me part numbers over the phone.

Any ideas?