Disappearing Coolant?

I have a 02 Grand Prix GT and my low coolant light keeps coming on, then turning off. Everytime i go to refill the coolant, the light will go off then come back on again. When i take a look at the tank the coolant seems to just disapear (and i have done this about 5 times, and i put a good amount in). I am pretty sure i dont have a leak b/c i dont have any spots on my driveway or any other signs of a leak. The engine runs at a normal temperature also. Anyone have any thoughts, were could all of the coolant be going? could there be a bubble in the system? or would flushing the system and re-filling it help? Bad switch or sensor?

Obviously coolant is being consumed probably in combustion. Did you check the oil for any brown milkshake including the radiator filler neck, reservoir and radiator cap for sludge? How is the oil level? Most likely bad LIM (lower intake) gaskets or even a UIM gasket as long as there is no external leaks.

idk about a bad gasket b/c i just changed the oil and it definatley wasnt a brown milkshake color. when i changed the oil i was down alittle bit, and theoretically if coolant was getting into the oil wouldnt my level be up? I havent checked the radiator cap for sludge or anything like that.

How many miles do you have?

I've worked on a total of six UIM and LIM jobs on SII 3800 engines and the symptoms vary. Two of the 6 just had unexplained coolant loss with no oil in cooling system or coolant in the crankcase. No DTCs, overheating or driveability issues either. One was detected after the return of oil analysis testing. Approximately 1 qt of coolant had to be added to the cooling system monthly. If coolant is getting into the crankcase you may not see it initially or visually but the bad part is it is causing damage to the camshaft bearings, crank and connecting rods bearings so it is best to nip in in the bud early on.

The only way you will know for sure is a visual inspection of the UIM and LIM gaskets after a tear down. Also, you can run a cooling system leak down test for bad intake gaskets which includes head gaskets before going into it.

The bottom line is if you do not see any external leaks then internal is the most likely and the UIM and LIM gaskets are typically the cause.

This pics shows the condition of the LIM port gaskets after removal on a SII 3800 with 130K miles. This engine had a coolant loss only with no external leaks but constant top off of coolant was necessary.

http://i5.photobucket.com/albums/y186/lizzywiz/DSC02590.jpg

I agree on the lack of symptoms other than mysterious coolant loss.

I've done quite a few of these jobs too, and the 99-earlier models have more UIM issues caused by the heat from the EGR stovepipe (there was a UIM revision in late 99) as well as the LIM gasket failure, where late 99-newer have more problems with just the LIM and UIM gaskets. As Bob stated, the only way to truly know the issue is upon teardown. My suggestion would be to replace both the plastic UIM (the aftermarket offers a kit with all necessary parts/gaskets included) and the LIM gaskets on any early-99 and older while you have it down and be done with it. On late-99 newer models, closely inspect the the UIM, as even though they are revised to alleviate the EGR stovepipe issue, I've seen some that start eroding around the coolant passages because of a faulty UIM gasket.

Since this a post 1998 Grand Prix with N/A SII 3800 meaning EGR stovepipe damage is highly unlikely I would carefully inspect the UIM plenum and UIM gasket but I would not replace it unless there was any obvious coolant passage damage or warpage which I doubt. Of all the '99 and up UIMs I never found one to be bad and reused them but of course with a new UIM and throttle body gasket. What I did note is the original GM UIM gasket flattens out over a period of time, age and mileage regardless of proper torque values on the UIM bolts. From my experiences the aftermarket intake gaskets made by FelPro are better than the OE GM.

This UIM plenum looks fine and was reused. It just needed a good cleanup to get all the old carbon out.

http://i5.photobucket.com/albums/y186/lizzywiz/uim_coolant.jpg

I agree with you 100% Bob. I expounded on the details to make the OP aware that there is a lot of misinformation out there (especially from the parts monkeys at the chain parts stores). I know a lot of people that have replaced UIM's when the didn't need to, and others that didn't when they should have due to a leaky UIM gasket eroding the coolant passages on the 99-up's. Exactly as stated, a thorough inspection is the only way to know exactly what needs to be replaced, as each of these seems to be different.

Also, one last note, GM now offers a metal-framed improved design gasket for the LIM on these engines. Fel-Pro still only offers a plastic framed design (although it is superior to the OEM gasket).

The problem with the latest GM aluminum framed gaskets is the silicone rubber used is still garbage although better than the previous gaskets. There are now anecdotal reports of failures on the revised LIM gaskets. Also, a complaint about erosion or deterioration of the aluminum on the LIM where the port gaskets are located requiring LIM replacement. Possible electrolysis.

I would use the latest Felpro LIM gasket kit only. Part number MS95809-1.

http://i5.photobucket.com/albums/y186/lizzywiz/DSC02591.jpg

I was not aware of the issues with the new GM gasket, thank's for the head's up. That doesn't suprise me one bit that GM can't even get a revision right!

Why hasn't fel-pro come out with a metal framed LIM gasket for the 3800 like they did for the 3100?

I put a metal framed fel-pro gasket in my g/f's 3100 GP when it blew the factory one at 65,000 miles. Almost 85,000 on it and not a drop of coolant less yet.

I ordered my parts, which included a new UIM, before I took the manifold apart. My old one looked really good but I put the new one on anyway and installed the newer version of the stovepipe that is a smaller diameter. That was about 40,000 miles ago and the last oil sample showed potassium at 4, the lowest it has ever tested.
Now if I can find the cause of that slight vibration in the engine.

If you have a GM car in the years '95-'98 with the Series II 3800 engine then you are better off upgrading the UIM preferably with the aftemarket Dorman or APN brands and installing the modified EGR stovepipe that come with those kits. However, the '99 and up have the modified EGR stovepipe installed on the LIM so there is nothing wrong with reusing the UIM if it passes inspection and just installing a new UIM gasket.

For the UIM gasket I recommend the aftermarket FelPro UIM gasket kit seen below over the OE GM.

http://i5.photobucket.com/albums/y186/lizzywiz/DSC02570.jpg