Ok so here is a weird one ... I am not a heat expert so I am hoping that someone on here can help me out. Last winter, the heat in my truck was great, it was hot and heated up quickly, so no problems. The temperature just dropped below 20 the last two days here so this is really the first time this season where I have had to use the heat. What is happening, is that when I am sitting still (just idling in a parking lot) the truck is fully warmed up and everything, the heater blows cool air, like it is mildly heated, but not really hot by any means. As soon as I start driving, or even if I just rev the engine to about 1500RPM, the heat instantly becomes super hot like it should be. Same thing, if I am driving down the street and the heat is blowing nice and hot, then I stop at a light, the heat instantly cools down. any thoughts??

 

insufficient flow through heater core at low rpm. possible air pocket - check coolant level (while cold) and top off overflow tank. but more likely you need to back flush heater core.

 

hmmm ... I will check the coolant level when I get outside. Is there a special kind of coolant I need to buy?

 

match your existing color - green or red.
for dilluting, use distilled water rather than tap water to avoid passages stopping up with mineral deposits.

 

if you wanna get an airbubble out without flushing it, park with the nose of your truck higher than the rear, take the radiator cap off, start truck and shift to neutral, turn heat on high and let it run... Once the thermostat opens up it should push your air out, then you can add coolant to get to necessary level and your all set...

 

Hanson ... that's a great idea, I will try that tomorrow. Thanks!!

dhvaughan - that's a great call about the distilled water, I've never done that before but thinking about it I don't know why I haven't!

 

well i got a problem with my heater. the passenger side blows nice and hot the way it should but the driver side is COLD like no heat at all and it does it through all the vents (feet, defrost, head, etc.) but i dont have dual climate controls so what could be going wrong? it is a 2003 1500

 

Ok, so turns out I was low on coolent ... I put in a full gallon of 50/50 mix this morning to bring myself up to the correct level. Unfortunately, it didn't seem to help on the way in this morning ... I'm thinking maybe the thermostat is stuck open?

 

I am having the same problem as nickbbb. I just replaced my thermostat. Now the passanger side blows nice hot air in a matter of mins. The driver side vents never seem to get hot. The hearter core is good and the coolant level is correct. Any suggestions?

 

watch your temp gauge from a cold start. if i rises from nothing to about 195 within 5 min or less, and then sits on 195 nice and proper, then the thermostat is good. if it take longer than that, or it sort on lingers around 130- 140- 150, or doesn't want to hold 195 nice and steady, then the thermostat is bad.

you may want to recheck your coolant level every couple of days. you want it to be where the overflow tank is at max level when cold, as well as the radiator full at cold. it may take a few fills to get it full and all the air out. caution never open radiator when not dead cold... i just added to my overflow tank each day until it stabilized. the radiator somehow sucks it in.