I have a 1999 JGC with the 4.0 motor. When running the heater it blows lukewarm air at best. Temps of the blown air are 55-60°. I flushed the cooling system and put new coolant in and then ran jeep for almost an hour to work out any air bubbles. Still not blowing warm. When I run it on the re-circ setting it blows warm air and is comfortable but the windows fog quickly. Coolant temps inside the motor seem normal and sit at 210 average.

That being said, if coolant temps are normal, my problem isnt the t-stat, right?

I'm thinking heater core but want to explore all options before I spend money on a heater core.

Any ideas? It's really cold where I live so heat in a car that I drive to work would be swell

 

I'll bet it's the "really cold" part. See if it gets warmer on a lower blower speed. Last year I had this same problem at -15*F outside air temp. I put it on recirculate and the heat was brutal. Back on defrost and lukewarm air. I figured out the air was going thru the core too fast to transfer heat. It worked much better on a lower blower setting then high. If your heater core is partially plugged with crap, that makes it worse.

The situation with me was I was driving around with the driver's window wide open delivering newspapers and it was hard to keep the windshield and wipers from freezing up. I had to stop several times and put the window up to get the jeep warm enough to continue. One of those times, I switched to recirculate and pretty soon I was sweating! I then switched to defrost and lowered the blower speed. Ta-Dah!

Try pressure flushing the heater core to be sure it's flowing good. Don't use more than a garden hose though.

 

Blend door may be broke. Common problem on the Grand Cherokees.

http://www.jgcparts.com/JeepHeater.html

 

Instead of starting a new thread, does anybody else have this issue? I flushed the core and that never really improved the situation.

Run on recirc: blows hot air
run on any other setting" blows lukewarm air, maybe 50-60 degrees

now in the summer, the AC works perfectly but just running vents temps blow about the same.

Does anybody have thought/vids on what needs to be done?

 

I'm having the same issue... I just had the heater core flushed and not even a week later the same issue... I want to get this resolved before it gets too cold.

2002 4.0L WJ

 

how does your oil look? could possibly have a cracked head which can cause heating problems

 

I know my head isn't cracked on mine I checked for hydrocarbons in my coolant and got nothing so no blown head gasket or cracked head. It seems to be doing better at the moment it's very selective.