In MI: I have a 1999 model with same engine…same symptoms…problems …etc. But here is a twist for ya…In the Summer when it is 60-105’F… the car runs perfectly fine…cool air …no leaks no problems. The car Temp stays at a steady 50% mark.
But, as soon as the air ambient drops below 55’…it heats up and has issues!?? It can be the dead of winter…10’F…and this thing gets hot! Today it was down to 35’ am…high of 45’F today…it ran hot at 75-85% mark most of the day. Last winter it did loose antifreeze and I had to keep refilling & watching the reservoir. If it is only trapped air…why does it only get hot when the weather gets cold?
Chevyguy28 have you resolved the problem yet? I had the same problem with my 02. It happened to be the thermostat. I changed the motor after this happened because my wife overheated and blew the head gasket. I put a new thermostat in from pep boys and the new motor still overheated. After some research i found out about a service update. This was for the thermostat. I guess the valve in it needed small slots in it to circulate more water. I was going to just drill some 1/8 in holes in the one I had but opted to get the right one from a dealer. It was more expensive but I haven’t had a problem in over 2 years. Hope this helps!