Thanks for the advice from each of you. The car does not over heat. It had a new radiator and hoses put on about a year ago. It does not overflow all the time. I did have to do a patch job on the inlet nipple to the tank because it broke off and I didn't want to replace it ($55 new). I inserted a brass tube thru the nipple to support it and epoxyed it together. It has held up well but maybe the openinig too small. Coolant does pass thru freely. I will get the tank checked for Co2 gas to see if this might give me a clue. Thanks again... AC