Hello everyone, I have a 2001 Chrysler PT Cruiser 4 speed auto (2.4L) with 148k miles (238k KM). When driving at 60 mph for at least 20 minutes it begins to overheat. I can hear the fan kick on when coming to a stop, and the thermostat, and radiator are both recently replaced, and the water pump is only like 2 years old. The coolant however is not original it is just. Prestone universal, all make, model, and color; 50/50 premixed coolant/ antifreeze. When it does overheat the only way to get it to cool down a bit is turn the heater on full blast and slow down. I have bled what I think to be all the air out of the cooling system and when it does get hot both the upper and lower radiator hoses are pressurized and warm. Keep in mind it is also below 40° F (4° C) when this occurred and it still began to overheat. The hottest it got was slightly above 3/4 mark but if it wasn't for the heater being on and slowing down it would've overheated completely. Could this be head gasket issues? The car does have quite a bit of mileage on it, but I've seen these go for a lot longer. Its been maintained regularly, and its not always beat on. The car shifts great and the engine runs well (sometimes in the morning ill feel a misfire for about 5 seconds and then it runs great this doesn't happen consistently but I think dirty fuel injectors might be to blame as I do also only get 17mpgs. But that's a whole different thing.. Currently I'm only concerned about the overheating issue) Anyways what do you guys think? head gasket issues? Or is Prestone really that crappy of coolant?? Any help is appreciated Thank You.