I think you have a 3.4L engine. The most likely suspect is a leaking cylinder head gasket. That can allow combustion gases to sneak into the cooling system. If it pools under the thermostat, it can fail to open resulting in no coolant flow. That means no hot coolant giving up its heat at the radiator and no hot coolant to the heater core in the dash. Thermostats need to be hit with hot liquid to open. Hot air won't do it.
Your mechanic can do a quick, five-minute chemical test at the radiator to test for one form of a leaking head gasket. That involves drawing air from the radiator or reservoir through a glass cylinder with two chambers partially-filled with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow.
Saturday, February 23rd, 2019 AT 3:10 PM