in the morning when im driving my 4 cyl. truck, if the heater knob is turned to the heat side ( does not matter if heater is turned on or not) the temp gage goes to a little over 1/2 way and then starts to go down to normal ( about 1/4 to 1/3 ). only does it after a cold start, once motor is warm dont have any issues. heres the weird thing. if i have the knob turned to the cold side in the morning it does not go over 1/4 on temp. seems to run cooler if i have knob turned to cold position. already changed thermo stat. what could it be? thanx.