When is it time to replace intake gaskets?

[ted4887]

Okay, here's the deal.

I have a 2002 Grand Prix with the 3.8L supercharged motor. Recently it started misfiring badly.

It's in the shop today getting new plugs, wires and coils... but my mechanic raised concerns that there is a little puddle of coolant near the gaskets. Could leaky intake gaskets be the cause for the spark plugs fouling out?

Forgive my ignorance, but I'm curious if I should consider fixing this before the problem gets any worse? If not, how do you know for sure when it is time to replace them?

[Scott K]

Yes it can cause it, or the plenum itself can be leaking by the egr port. I would pressure test the cooling system and see how bad the leak is.

[Eric Wettschreck]

I'm of the thought that you replace parts when they are faulty, or you know they are soon to be faulty, and not just cuz.

Having said that, 4WE is spot on. A pressure test will tell you if/where the leak is.

[lotsofish]

It's a common problem with this motor. I had a 97 that I had to replace the intake manifold gaskets twice on. Check your oil to see if it looks milky. That would be water/coolant getting into the oil, which obviously is not a good thing.

[Jeremy airjer W]

It's a common problem with this motor. I had a 97 that I had to replace the intake manifold gaskets twice on. Check your oil to see if it looks milky. That would be water/coolant getting into the oil, which obviously is not a good thing.

You probably had a 3.1 liter which had its own set of problems with the lower intake gaskets. The 3.8 liter has an issue with the upper plenum rupturing which causes an extreme coolant loss internally. This usually results in one or more cylinders hydro locking. The external leak could be in between the throttle body and the plenum, which is pretty common. The plenum would be replaced, or should be replaced if it has not already been replaced.

If the leak is from the lower intake and on the drivers side than the lower intake gaskets still need to be replaced and again replacing the plenum at this time would be a wise choice.

If the leak is on the passenger side than I would be suspicious of either the coolant nipple or elbow (I don't remember what year they switched) that is in the lower intake right above the water pump.

[lotsofish]

You probably had a 3.1 liter which had its own set of problems with the lower intake gaskets. The 3.8 liter has an issue with the upper plenum rupturing which causes an extreme coolant loss internally.

It was the 3.8 (not supercharged). The lower gaskets had broken down similar to the problem they had on the 3.1's and slowly leaked coolant into the oil... twice.

[Jeremy airjer W]

Interesting, I can't say I have run into that on a 3.8. They are typically external leakers and usually replaced because of oil leaking more so than coolant.

[NIBOWMAN]

Ted4887 said that he had the supercharged 3.8. This engine does not have the plastic plenum with the leak problem at the EGR port. I have seen a couple SC engines with intake leaks, typically external. Do a pressure test and find out where and why before just throwing parts at a perceived problem. Just my opinion.

[Jeremy airjer W]

Ted4887 said that he had the supercharged 3.8. This engine does not have the plastic plenum with the leak problem at the EGR port. I have seen a couple SC engines with intake leaks, typically external. Do a pressure test and find out where and why before just throwing parts at a perceived problem. Just my opinion.

Yup, missed that part!

[ted4887]

Thanks a lot guys! I'll get it pressure tested next week and see what the guys say. I've had bad experiences dealing with this stuff, and just want to see if I'm being fed a line of carp, or if the mechanic is truly right about it needing to be replaced. A lot of my hesitation comes because it's a new mechanic that I've never dealt with. Will probably get a second opinion on it, just to make sure.