My car had recently had a pressure cap issue and I replaced it several time and had the water pump and timing belt done and any time I replace the cap it still just builds up pressure like the thermostat is stuck could this be something happening??
If you get heat at the center vents with in 5 minutes of driving I doubt you have a thermostat problem. How much pressure build up do you have? 16 lbs. of pressure is correct. If you are blowing out coolant like a geyser with the radiator cap off while parked you either have a coolant leak and air in the cooling system or a bad head gasket. If your temperature gauge fluctuates you have an air pocket in the motor.
Head gasket or cracked head.
Caps are suppose to build up pressure. That's why they have PSI ratings on them. The thermostat has nothing to do with it. Even if a thermostat was stuck closed, which hardly ever happens, the cap would keep the pressure at the right level.
Head gasket. Have a pressure test done on the system. The aluminum cylinder head is the scourge of the earth. To save 20lbs, they went to an aluminum head on a cast iron block. Can you say dissimilar metals? Just WRONG!
thermostat can cause that, could also be an airlock stopping the thermostat from opening
head gasket leaking if its bubbling in the radiator consantly get the cooling system pressure tested will prove its leaking or not otherwise do a compression test