I've got a 2002 with a 3.8 V6. I've changed the water pump, bypass elbow, thermostat and radiator cap. There are no visible leaks, no coolant on the floor underneath, no water coming out of the tailpipe and there is no coolant in the oil. But continuously the coolant disappears somewhere. The only thing I can think of is it is leaking into the exhaust flow and going out the tail pipe as vapor. Has anyone else heard of or experienced this problem?

 

look closely around where your intake mates up with the engine block for any yellowish stains. May have an intake gasket leaking.

 

i had a similar situation with my LeSabre and it was the lower intake gaskets. it's a known problem.

 

^^^ these guys are most likely right, you could rent a cooling system pressure tester from your local parts store and do a pressure test. while its pressured up you can look around for any leaks. a coolant hose can have very small holes that only leak a small amount and only when the system is pressured up during operation. i had this happen, coolant never made it to the ground where i parked and i could not find a trail. pressured up with a pressure tester and poked and pulled on the hoses finding one by a clamp that only leaked when i poked on it with a screw driver. was not poking very hard so as not to damage a good hose.

 

My money's on the intake gaskets too.

 

I've had other GM vehicles and the intake gasket always seems to be the problem when the coolant goes "missing". I would agree that pressure testing may be the best way to diagnose the problem. Hope you find the culprit.

 

I'm not mechanically smart, but I have a friend that had the exact same problem. He had replaced a bad radiator, and went ahead with water pump, thermostat, etc. Turns out the new thermostat was defective. Replaced it again and all was good.

 

I will post my end results in a few weeks but I did my intake gaskets Wednesday and they looked very simialr to the ones in the pics. I also had coolant disappearing. I have to say this is a beast of a job to do. I started a 8:30 in the morning and did not finish until about 7 that night with only one hour long lunch break and one 45 min trip to the parts store. For anyone thinking of doing this themselves. Figure about $125 between gaskets, oil and antifreeze. If you pay to have this done figure on about $5-600