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This issue is fairly common on these vehicles. there are a few things to check, not assuming you are auto savy. first off, check the coolant fill cap. check for swelling of the gaskets. The lower gasket should be slightly smaller in diameter than the valve plate. The cap should be rated at 18PSI. If not, get one that is. Each pound increases the bointing point 3 degrees. Also, check to make sure the radiator and the trans. cooler are free from debris outside and in-between them. If your PT has a Turbo, make sure there is no debris between the intercooler and the radiator. Check your coolant levels. These vehicles have an issue with bubbling into the overfill.