98 Jimmy problem with heat

Started it and let it run for about 10 minutes to warm up with defroster on. Get in it its cool in the truck no heat so i start down the road and its starts to blow hot also noticed the temp gauge up around 210 then once it starts to blow hot it falls to about 190. Thermostat stuck? Also, got back in after about 5 hrs. and it works fine.:screwy: Need help please its cold out there.:frown:

Armallard

With the engine cold, take the radiator cap off and make sure the radiator is full of coolant.

given the time of year my freind, i would flush radiator and replace thermostate. Its to early into winter to start havin those problems

I have the same problem will check levels however when I set it to vent and I turn the temperature adjustment when it gets to certain position I can hear a tea kettle like whistle, any ideas on that?

One more thing I just thought of when I come to a stop the temp will rise and when I start again it will fall back tot he normal range.

FYI there is no coolant leak in the passenger compartment or the sweet smell either

TIA
Rick

One more thing I just thought of when I come to a stop the temp will rise and when I start again it will fall back tot he normal range.
Rick

stuck thermostat. at idle the water pump isn't pulling much coolant from the radiator letting the engine get warmer. as soon as you accelerate the pump pulls in cold coolant from the radiator since the thermo is wide open. replace the radiator cap at the same time, they're cheap and work as hard as the thermo so should be replaced at the same time.

Changed the thermostat once will try the cap tomorrow and have topped off the fluid.