this one is strange...i've already put a new thermostat but my truck's temperature shifts between 170 and 220 degrees, then the temp is on the high end (should be at 190 but is around 220) then the heater doesn't work....its almost as if there is no water/coolant traveling through the engine....then after a little bit the temperature cools off again to 190 or 180, even 170 at times, at this point the heater works perfectly...i thought the themostat was being retarded but thats not the case....could the impeller in the water pump not be working properly?

 

my first guess is that you've got air in the system. the air could be a result of changing the t-stat, or it might be getting sucked in from a leaking hose, hole in heater core (steam and odor), or around a leaking water pump, radiator, or rad. cap. you could try removing rad cap and let it sit and idle for about 10 min to burp out.

my second guess is that might have a cracked head or leaking head gasket thats putting compression into the water jacket, which really screws up water flow. you could do a compression test or leak down test to rule this out. i hope its not this.

you might try another t-stat or just remove your to verify that you didn't get a bad one.

 

thanks buddy i'll try that