The reason this problem started was because i was driving on highway and i went to 19psi , out of no where coolant sign came on / overheating needle went almost to H . and i took the exit went to gas station looked at my coolant it was full , so i let it cool down and then drove it home slowly . next day it's not really bad over heating but when ever I start my car and let it warm up , so far it's good . The needle goes right in the middle and stays , so i keep driving and about 10-15min later, the needle goes above middle and I can hear the fans being on . It doesn't keep going up but it actually fixes it self and goes back to normal. But sometimes it stays between the middle line and the next line . I don't let it reach Hot . So I turn the heat to full blast . I also had my water pump done 28k miles ago with the timing belt and tensioner . Also I did coolant flush today. I'm not sure what the problem is , is it thermostat ? Also I tried if I keep heat on full blast the car goes back to normal temp and it will sometime raise up and then come back to normal after a min. I'm not sure what the problem is.