Truck doesen't warm up until driving - no matter how long idling

[work sucks]

I've got an 04 silverado 5.3 that will not warm up while idling. If it has idled for a good 15-30 minutes or more, it still blows cold air until I drive it. I first thought thermostat, but it does the same thing in the summer with the air conditioning. (won't cool until driving) And... at a stop sign or other stop in the winter it will again blow cold air and warm air in the summer. The temp gauge goes up as it should and then drops when I assume the stat opened. Any ideas??

Thanks

[Pinusbanksiana]

Stupid question, but is your coolant level filled all the way to the top?

[BobT]

The heat part I can understand, especially if it is a diesel. Diesel engines run so efficient that it's possible they could idle all day and not reach running temperature. That's part of the reason, contrary to popular myth, it is NOT recommended to let them idle for extended periods unless you have a means to raise the idle rpm during that time. My understanding is that a lot of truckers have a manual throttle they use for this. My 1985 Ford 6.9L would cool down if I let it idle for very long.

The AC part has me baffled a little though because that works off a compressed system and your fans should be running to draw air through the radiators.

[gregg52]

i have a gmc yukon xl 2000

now that you say that one time my heat didnt work at all it blew cold air

the next time and forever after its fine not sure what that was all bout

bout i think something stuck in the heat vents or something

maybe for some reason they wont open i dunno

like the guy said above be sure the coolant is full

bobt your right if you going to leave a diesel run all night you should bump it up a few rpm to get oils around the bearings

theres a manual throttel on trucks

[delcecchi]

I've got an 04 silverado 5.3 that will not warm up while idling. If it has idled for a good 15-30 minutes or more, it still blows cold air until I drive it. I first thought thermostat, but it does the same thing in the summer with the air conditioning. (won't cool until driving) And... at a stop sign or other stop in the winter it will again blow cold air and warm air in the summer. The temp gauge goes up as it should and then drops when I assume the stat opened. Any ideas??

Thanks

I think I know this one from listening to car talk...

The vacuum to the doors in the ducting under the dash, whatever the name of that is. Controls the air flow. Check the vacuum or the hose to the motor that controls the air flow.

[Macgyver55]

I believe that the heater contols in this vehicle are not vacuum operated. Rather, they use small electric servos in place of vacuum ones.

[jwhjr]

I believe that the heater contols in this vehicle are not vacuum operated. Rather, they use small electric servos in place of vacuum ones.

Correct. I had to replace the driver side blend door actuator in my 04, and they are definitely not vacuum operated.

[work sucks]

Thanks for the input guys, gives me a few thongs to check!

[caughtacase73]

I have heard that in an attempt to make newer vehicles as efficient as possible that most of the pullies / pumps under the hood are undersized. In theory this takes less effort to turn them. Not until a higher rpm will they really start to get things moving and produce more heat. Not sure but seemed to make sense to me. I have a dodge and get the same results. It will warm some while idling but will not give me hot air from the vents until I start driving.

[Macgyver55]

Thanks for the input guys, gives me a few thongs to check!

Checking thongs?......sounds intriguing on the proper model!

[Dave S]

Checking thongs?......sounds intriguing on the proper model!

+1

RFLMAO

[delcecchi]

I believe that the heater contols in this vehicle are not vacuum operated. Rather, they use small electric servos in place of vacuum ones.

Well, so much for a good theory.

[Macgyver55]

Well, so much for a good theory.

And a good one it was on other/older vehicles.

[walleyehunter80]

the coolant level is what the problem is ................fill er up bud

[randerson]

Might need your coolant system flushed a buddy had to do it on his 02 I think the heater core gets pluged