'98 Chevy Lumina-Coolant reservoir won't stay filled

Also temp gage fluctuates while driving, but does not show to be running hot. No leaks can be found. Have filled and by the next day the reservoir is empty and the radiator not full. What is up w/this? Where is it going??? Using GM Coolant mixed 50/50 w/water. :confused:

How about posting in the correct FORUM, lop?

Check your oil... does it look like a chocolate milk shake? (Leaking head gasket). Does your car run ok other than losing coolant? When you filled the cooling system, did you bleed all the air from the system? (your temp gauge will fluctuate with low coolant)

Be absolutely sure that you don't have an external leak somewhere, like the water pump (the weep hole will drop coolant and is not so easy to detect without a coolant system pressure tester). I don't know of any part stores who actually carry coolant system pressure tester for rent, I ended up buying my own (most of the stores I asked, thought I was talking about an antifreeze solution tester). A radiator repair shop would have them though.

any white smoke coming from the tail, could be head gasket or intake manifold gasket they are pretty common. You can also do a compression check in the cylinders, to check for that head gasket just to be safe. I assume you have a 3.1 ltr.

Mine was doing the same thing but little at a time could not notice steam out of exhaust. went for 2 months. Pressure in cylinders was within 5-10 lbs on all 6 of them. Still had to fill reservoir every two weeks then boom head gasket failed end of sad story.

Thanks guys-It's going to the shop soon-the head gasket thing is my luck and I don't notice any smoke or anything either...we'll see.

just went thru this on a 96 lumina 3.1
looked at first like the oil pump was bad (it was too much coolant i guess) replaced the pump and a week later checked the oil and it was milky.my temp gauge also fluctuated, but never went very high.
turned out to be the lower intake gasket. chicago area cost at a local garage was $512.00 complete. bit the bullet and had it done and am very pleased with the car. (bought it as a work vehicle for 380.00, spent 200.00 on the oil pump and 512 on the gasket) now the only problem left is the paint. almost 1/4 is gone... primer issue i guess