Thread: how do i know if my lower intake manifold gasket is bad?

like the title says how to i know if my lim/uim is bad on my 99 gtp

Are you losing coolant? Gtp doesn't have upper intake just the supercharger and LIM. LIM gaskets can leak coolant into the air side of intake or into the oil. Original gaskets are black plastic, the replacements are aluminum.

i dont know if im losing coolent i have no way to tell, i know they have super chargers theres still a gasket though is it not called the UIM gasket?

Upper is a supercharger gasket and it's not a problem just the lower on the supercharged cars. Check your oil for coolant and look around your LIM bolts for coolant puddles.

hmmm ill check the oil dont really know where the lim bolts are though

Just look between the Head and the LIM and you can see if the LIM gasket is black or if it's Metal, if it aint metal change it, don't wait for it to fail because it will, potentially causing you a blown up motor

hmmmm ill take a look tomorrow, if it fails or is failing will i know before the engine blows like will the car run worse?

Well that sort of depends, sometimes you'll notice you have to add a little coolant every now and then, other times the beeotch can dump alot of water into the valley. Question is do you want to chance it? I have 5 cars with 3800's after the first one needed LIM gaskets they all got LIM gaskets, every one of the Intake gaskets was leaking to some extent. The longer you wait the more potential for more serious damage you have. Sort of like how long would you drive a round with a nail in your tire if you knew the nail was there. It's a crappy design that will fail for sure, and I wouldn't waste time waiting on it to do so.

how long does it really take to do a lim? my buddy took 3 days to do his but his was like a paste and needed a lot of cleaning and i say a video of it being done in 35min whats realistic

coolant hasnt gone down, oil looks fine cant see any puddles around the bolts but heres the thing theres this gunk all over my engine on that side (by the lim bolts) its really thick and black idk what it is or where its from

I wasnt leaking coolant in the oil, or anywhere for that matter. But when i took the LIM gaskets off for my topswap they were cracked where they always fail. Ive never seen a pair of the plastic LIM gaskets that werent cracked. Change them if you can. Its not hard, just a little time consuming.

oh no i am for sure gonna do it because the rear valve cover is leaking and my s/c is bad so im already half way there at that point i might as well do the lim its just i wanna know how high this should go on my priority list ya know?

Why do you think your sc is bad? If you have the sc off it's only ten or so more bolts to do the lim.

Lim's don't often leak enough coolant into the oil to see it. They sometimes allow a little cooalnt into the cylinders and you might get light misfires.

The SC gasket is referred to as a plenum gasket. It can leak. I've seen this occur when one of the o-ring has an issue.

The s/c is bad because it sounds like a bad bearing and a bad couplur ill try to get a video later today

Originally Posted by andremike

All this talk about coolant in the oil... I see oil around my LIM and also see oil on my garage floor. I am told the oil is pooling around the bolts and leaking down.. Is that a sign of a broken LIM

chances are you have a oil leak, (valve covers or oil pressure sensor or oil pan) and your lim bolts are seeping coolant, just like mine have been for 6000 plus miles.

i have 2 bolt valleys that have coolant in them, and one at the end that coolant runs off the side but steams off before you would know it was there.

i also have the old plastic gaskets and should change them on general principals but i am letting it go for now.

i'd address the oil leak first.

<Jumps up on soapybox>

Valve cover gaskets, oil pan gaskets and rear engine covers are the most common external oil leak areas of a 3800.
If you have oil or coolant in the valleys of your LIM, it means your LIM bolts are no longer sealed and seepage is occuring. Clean it and see how fast it comes back. Likely you'll give up waiting on it.

LIM gaskets 99% of the time do not allow coolant into the oil. This is a misconception just like the thought that when an L36 UIM fails and dumps coolant into the intake and fills the oil pan, it does not fill the oil pan with coolant.