Chrysler Repair: CHRYSLER 300M OVERHEATING, blown head gasket, vacuum leak

Question
I HAVE A 1999 CHRYSLER 300M.THE PROBLEM I'M HAVING is THAT I CAN START THE CAR AND LET IT RUN FOR AN HOUR OR SO SITTING STILL AND IT WILL NOT RUN HOT.But if I drive it a couple of miles the temperature gauge goes up on hot,and starts overheating.I've changed the thermostat,But still have the same problem.I took the car to a near auto shop in town To put on a machine to diagnosis the problem. They told me that the diagnosis came back as code #2 meaning that the car has a vacuum leak and my have a blown head gasket,cracked block,or worst case it may need a new motor. They wouldn't know until they break the car down. I don't think that sounds right.I live in a small town with about 3 auto shops in that town, and the Chrysler dealer is about 100 miles away.I think that they are trying to get over.Im not a mechanic, but if the car does have a blown head gasket or a cracked block, it would have water mixed in the oil that looks like chocolate milk on the oil stick and it would be gray smoke & steam coming out of the tail pipe.I don't see nothing of that nature going on with this car. Please advise.

Answer
Well I can say that I've seen lots of blocked coolant passage ways in the Cylinder Heads from poor casting in the Aluminum Heads on these cars. I do about 5 of these repairs on this engine a year. This is what happen the aluminum from the head gets coarse and starts flaking off the head. Then the metal particles find a spot on the head to rest normally right in the water jacket as time goes by more metal flakes and carbon and any other crude that may find its way into the engine start sticking to this area blocking the water passage way making engine overheat because of poor coolant circulation. If you do take it to the Dealer there is a Technical Service Bulletin on this issue under Star online The Dealer will know what I'm talking about. But if not definitely make sure your fans are working correctly.