My wife'* car has been losing about a pint of coolant a month for the last 45000 miles. It does not leak out anywhere that I can see and the engine runs fine. When I change the oil every 3K miles it looks normal. We had the upper intake manifold replaced at 60K, but it made no difference. Any ideas as to where the coolant is going? Thanks, Jim

it would seem that your upper intake OR the lower gaskets cause im guessing that they were not replaced at the time of the upper...GM has come out with new metal lower gaskets

I agree with 1993 SLE. If the LIM gaskets were not replaced when the upper was done, they would be the prime suspect. If they were changed, you might have a pinhole in a hose. I had one of those once that would only leak hot under pressure. Very hard to find, and the stream was so small that it would vaporize on the hot engine before getting anything wet. A cooling system pressure test should help you narrow down the possibilities.

I had coolant loss for about 10k miles before I could find the leak. Although the leak was from the UIM, I replaced the LIM at the same time. It too was worn thin in places and would have been the next to go (if not already)

My coolant was leaking where through where the bolts were located. In the below pic - under the wires that go over the UIM.



....it would pool around the bolt and then evaporate, making it difficult to detect...untill it started to leak worse.



My leak was on the lefthand side, however I could see remnents of coolant on the right.

I'm not sure if they replaced the LIM gaskets when they did the UIM. Having the cooling system checked might be a good starting point. thanks