Thread: LIM Gasket, Head Gasket, or bad sensor?

I've been researching and troubleshooting this problem for weeks now but I'm starting a job 1.5 hours from home tomorrow and don't trust the GP right now. So to the rental agency I go!

But on a serious note, I honestly can not find a solution to the problem (which yes there could be more than one). But any and all input would be quite beneficial and appreciated. Here is the problem:

Car: 1999 GP GT, 3800 VIN K with 102K

Stalling. Over the summer, I was driving the car maybe once a week ... in stop & go Boston city driving. The car would stall 2-3 times on a 5-10 mile trip when coasting or at a stop. I figured b/c not driving it often, the computer wasn't adjusting properly. I've been driving it daily the past 2 weeks and seemed to have fixed itself. Initially it was at city speeds, but also died on me on a highway trip going 60 mph. Vacuum fitting are somewhat corroded, but I have siliconed everything I could find until I can afford a new set ($200 from the dealer!)

Ticking. In the past month, ticking has been coming from the lifters. At first it seemed to be coming from the front, then more recently from the back. It would go away though after pressure built up. Low oil? Low oil pressure? Either or... I did a change last week and the problem has seemed to vanish.

Overheating / Leaking. I put in a new thermostat and radiator cap in after the cap blew about 18K mile ago. Good to go. After the oil change last week, the car seemed fine. After a 400 mile trip over 3 days though... I have some serious overheating/rough idle issues.

- Cap was bad again. Replaced and now have vacuum pressure (I could squeeze the upper radiator hose completely before).

- However, now the car warms up and warms up fast. I can sit on the gas at about 2K rpm in the driveway and the car will be up to 210F in under a min from a dead cold start. And after 5 min of 40 mph driving, its over 235F but not "overheating".

- Low coolant. Light has been on for over a year so I lost faith in that aspect awhile ago. I've put a gallon of Dexcool in the past week both from the reservoir and straight into the radiator from the cap though. Still very low (reservoir empty this morning) and NO signs of leaks under the car.

- No white smoke from the tail pipes, but a lot of condensation on hands.

- The car is sluggish.. had complete loss of power at 25 mph yesterday from cold start. Pulled over, turned off and on.. and I got home ok. Still idling/running somewhat rough.

- Wouldn't start... once. When car "overheated" to about 240-245F, I pulled over and shut her off for about 5 minutes. I know the computer shuts off coils/cylinders? in this instance to prevent further damage.. but it wouldn't start at all. It would struggle for gas it seemed and would cut right out. After a minute and giving it some gas (2-3K rpm) it finally started but was really struggling to stay running. I limped home.

- No signs of coolant in oil. No milky-ness. Fresh oil change, bad or good to decipher?

These (-'s) are my symptoms. Out of everything I have found... I think its the LIM gaskets. Could be easy fix, but want to be reassured before I waste time and money. But from reading the forums, it could be a Head gasket, a sensor of any sort (MAF, radiator temp, ...??), or even the computer could be bad or needs to be reflashed.

Any and all help would be appreciated. Although I don't post or respond that much, I read them all the time.

Originally Posted by matt5112

If your LIM gaskets have never been changed then do that and see if it improves.

Guy at work had this issue, changed the LIM gaskets and put a new upper plenum on (old one warped) and it runs a million times better now.

Make sure you get the aluminum ones.

But if you want to be sure about the head gaskets do a compression test and/or leak down test.

For a leak down test, you use a 'leak down tester' correct? If so, where do you get one because Autozone didn't have one to rent?

Oil is not milky which is why I think LIM. Water is coming out of the exhaust at a slow rate, but doesn't smell sweet if it was coolant.

I'm gonna do the LIMs and MAF. Cheap and quick enough.

Where can I buy an aluminum plenum? Haven't looked toooo hard but google isn't showing any immediate help/

maybe a junkyard but that would be hard to find, maybe in the for sale section on the home page? some1 could be selling the top end after a top swap

You don't need an Aluminum Plenum, just a good plastic one the is not melted between the two coolant ports and the EGR port, located on the bottom side close to where the T/B connects. Yours may or may not be damaged, I have pulled several apart and only seen 2 failed upper plenums.
For the LIM gaskets make sure to get the Aluminum style from either Felpro or AC Delco

i didnt read your book, i might later. sorry im not actually contributing to this thread, BUT...

THANK YOU for being one of the only people in the history of the internet to actually describe what is going on in extensive detail in all areas. you are a master of your craft.

For those who read this in the future with any of the above symptoms.. the problem turned out to be the Upper Intake Manifold (Plenum). When the old one was taken off, the LIM was FILLED with coolant. Scary stuff.. it could've ruined the motor. Luckily it wasnt running when it hyrdolocked.

An easy way to test is to take off the the intake... open up the throttle body to see any signs of coolant (fresh or residue). But that isn't always the case.. just mine.

For those who don't know (which I didn't prior to this) the plenums are defective and melt/corrode fast around the EGR valve. The new valve is much narrower so the heat of the aluminum won't melt the crappy plastic intakes.

New LIM gaskets, UIM/plenum with new gaskets, thermostat, plugs, and 3 oil changes... the system is running great. SES light went off on its own and now getting 25+ mpg.

It was weird.. it was literally straight dexcool coolant ON TOP of the lower intake manifold. Oil I believe is a sign of the head gasket beginning to deteriorate.

The throttle body had crusted orange/pink residue in the grooves and around the sensor. But there was a black build up on inner side of the throttle body.

For the EGR valve.. you could replace it to prevent any further damage. But you should check the plenum when you have it off anyway to see any signs of corrosion around the valve. The two holes opposite each side of the actual valve was where the problem truly was. The coolant was boiling around the valve to the point that it would splash up and corrode it. Over time.. it just completely wore through the gasket and plastic.