Originally Posted by PsRumors
My wife'* 98 Bonneville is going through a gallon of coolant a week. There does not appear to be any external leaks. After reading the archives I figured upper intake.
I had her drive the car slow, fast, hard, easy, and normal while I followed behind her. There are no signs of condensation in the exhaust. The car can idle all day long and there is no coolant loss it only happens when she drives the car.
Is there any thing else to look for? There doen't appear to be anything on the block. Is there any way to check the intake without pulling it?
This is the EXACT problem I had with my 98 Bonneville. I even drove her from DC to Ocean City, MD and back with the problem. No condensation, no leaks, nothing. Without condensation, or coolant in the oil, it'* not the head gaskets.STOP DRIVING IT AT ONCE OR YOU COULD LOSE THE ENGINE!
Pull your front plugs and stick a new pencil into the cylinders. Check the eraser for wetness. It'll be there! It is probably the lower intake gaskets, but when you remove the upper plenum, you'll be hard pressed to reinstall it without damage. The rubber seal (gasket) for the throttle body is probably bad as well. You can get an upper plenum from any GM dealership. Don't go used on this part, you'll be sorry down the road. My new U.P. cost $300US.
Once you get the plenum off, you should see quite a few swimming pools of coolant in the recesses. Dry these out completely before you pull the lower intake. There are 2 bolts you need to remove that are hidden as labled on the upper plenum...(facing engine)one in the upper left and one in the upper right. The job is really well layed out in the Haynes manual for our cars.
If you haven't yet changed your thermostat to a 180, this is the time to do it. That will stop this from happening again any time soon. Good luck!