My 96 LSS does not seem to be transferring overflow coolant back into the radiator. What I have done so far is replaced the radiator cap (twice because I thought the first cap might have been defective) and had a mechanic pressure test the system with up to 15 lbs. of pressure. The pressure test revealed no loss in pressure so the cooling system seems to be intact.

A little history on the car. The radiator is a new one, replaced due to an accident. The car does not overheat at all and there are no problems with the engine that I can tell (no loss in power, no drop in gas mileage, no sign of coolant in the oil, no steam coming out of the tailpipe). It has 183,000 miles on it but runs like a champ.

The only problem I am having is that the coolant from the overflow tank will not return to the radiator. I have to top off the radiator once a week to make sure the engine has a sufficient amount of coolant. Has anyone out there experienced this problem? Let me know if I need to add more detail. Thanks in advance!