Used the search, didn't mind much -


Ambient temp is high 20s to low 30s. At idle I get almost no heat - wait, let me finish...

Even after the truck warms up, at idle the heater is blowing borderline cold air. However, when it is running at 1500 - 2000 RPM I can barely hold my hand in front of the heating vent. Hate it think it's a water pump but not sure what else would cause that...

I flushed coolant about a week ago, this is the first time it's been cold enough to really use the heat, Could this also be a symptom of air in the heater core?

 

have you checked the coolant level? Sounds like might be low.

 

Yes, coolant is where it should be. I'm thinking air bubble in heater core.

 

These engines at idle are barely heating 300°F EGT. Most of that heat goes out the exhaust, Some into the oil and out the Oil Cooler and some makes it thru the block and into the Coolant.
It takes a while to warm up a cold soaked engine block. And it's not producing a lot of heat to even maintain coolant temps when sit and idle.

contrast that to having 800°-900°F EGTs when you have 15-20 lbs boost going through a working engine

What are your coolant temps at idle when you have no heat?

 

I've started a new thread, turns out there is plenty of heat at idle, but it's only on the passenger side.

 

If you have dual zone climate control, you may have air in one of the cores. Did you pull a vacuum on the reservoir after changing coolant?

 

That's a good thought, I will be pulling vacuum on the system tonight.

It's really strange as I'll get heat if the rpm are 1500 to 2000, other than that nothing.

Also discovered this morning that the hubs aren't engaging with 4wd. Had to manually lock the hubs in order for it to work.

 

Having same exact issue have you found the problem.