Last week the temperature gauge on my 2009 Journey 3.5 started fluctuating erratically,going from Normal to the Overheating warning and back. Sometimes it would drop back to Normal but then start climbing again but stay below overheating and then drop again. I assumed I needed to replace the thermostat, which I did this weekend. After replacing the thermostat and putting everything back together, I filled the coolant reservoir to the Cold level and ran the car for several minutes with the cap off, topping up the coolant as needed.
Then I took the car out for a test drive. She ran well until the gauge reached operating temperature but then started fluctuating again.
This morning, with the engine cold, I parked the car nose up on a hill and tried burping the coolant. Nothing happened. She ran okay until I drove the two blocks home and then the gauge started its old tricks again. As near as I can tell, I still may have air in the cooling system, another bad thermostat or a faulty sensor. Does anybody have an idea of what else I can do to solve this problem?

 

My 2015 AVP was having chronic overheating and it ended up being the 2nd smaller thermostat! (Yes there is 2)