I have a 2001 Duramax that has a pressurized coolant system. Pressure will force coolant out overflow of surge bottle. Have had to shop 6 times. Coolant analysis says coolant has no contamination. Mechanic at shop verified coolant as non-contaminated. Glow plug test, on cold engine, shows no misting. Truck has never overheated even in summer pulling 10,000 lb travel trailer. Having trouble with heater/defroster. Truck runs great most of time, no smoke, vapor,loss of power, leaks, etc.
Shop mechanic ruled out head gasket after tests and test drives. The best option offered for repair was injector sleeves, which have been done, ($1900) and both thermostats have been replaced ($330). Problem still exists. I think the shop may still say head gaskets are the issue. That repair will be $2400 if GM pays half or $4800 if GM will not as truck is out of warranty. Has anyone solved this problem?