No heat at idle?

[05spudman]

If the truck idles there is no heat. Rev it up a little and the heat comes back? What would cause this? Water pump?

[kinnisoj]

If this was my truck the first thing I would do is change the thermostat. Possible stuck open or only doing the partiall open thing. Then if no change I'd start looking at the water pump. Just put in the BPD water pump. Shame you cant see it...not to difficult

[Colin7.3]

Water pump is shot

The blades are worn down enough that it does not have enough force to push coolant all the way to the heater core. Eventually thus will deteriorate enough you will develop over heating problems

Beamed in from the Death Star with lasers and sh*t

[mhatlen]

I just did a coolant swap from Gold to ELC1 and pulled my thermostat and drained out system and refilled with distilled water and a cup of dishwashing liquid soap. took for a 30 minute drive and drained and flushed with distilled water. Repeated 3 times and installed new thermostat along with ELC-1 coolant.
A bonus was heater is hotter and now my temps are a steady 194 +or- a degree or two.

I would try this or thermostat alone first and see how it does, just dont put tap water in it the minerals will raise hell with cooling system...........

[amdriven2liv]

Check for vacuum leaks, or might be the vacuum pump.

How is your coolant level? Done any work on the truck lately?

Oh, turn it to "air", does that only blow out the defrost?

[Term3]

When your checking the coolant level check for any evidence of coolant around the recovery bottle cap, wetness, white deposits. If there is you have a bad head gasket and its filling up the block heater with gases since that's a high point and once you are up in RPMs the water pump has enough force to push those gases out of the heater core and then give you good heat inside. You can also verify this with the coolant test strips for exhaust gasses from your local parts store. Sorry in advance for the bad news.

[mhatlen]

Originally Posted by Term3

When your checking the coolant level check for any evidence of coolant around the recovery bottle cap, wetness, white deposits. If there is you have a bad head gasket and its filling up the block heater with gases since that's a high point and once you are up in RPMs the water pump has enough force to push those gases out of the heater core and then give you good heat inside. You can also verify this with the coolant test strips for exhaust gasses from your local parts store. Sorry in advance for the bad news.

Ouch, he didn't mention any coolant issues and same thought went through my mind but unless there is a consumption issue I would be thinkin radiator and thermostat.

Thats a BIG pill to swallow if your right. lol

[sinner6.0L]

When you've exhausted all other options take a look at the headgaskets. Like stated before they will put air pockets in the cooling system and get trapped in the heater core. Headgaskets won't cause coolant consumption, it may or may not pressurized the degas bottle to the point of blowing coolant either.

[Term3]

Yes, it depends on how bad the head-gasket has let loose. Most guys envision a bad head-gasket looking like Old Faithful blasting out their degas bottle when it can be just just a trickle of exhaust gases bubbling into the cooling system and venting out the cap with little or no trace.

[Term3]

First of all to rule out the thermostat since they usually fail wide open. If your not able to get up to normal operating temperature doing normal in town driving then your thermostat is bad. You can't go by the dash water temperature gauge which is basically useless. Get a real gauge or borrow something like a AE. It could be a bad water pump but personally I've not seen many that bad to cause this without also causing overheating when the motor is worked hard.