Longtime lurker, new member here. Thought I'd ask for your expertise here, if anybody's got some time... I'm kinda stumped.
My '99 TJ started blowing cool/lukewarm air out of the heater vents. The upper hose to the heater core is pretty warm, while the lower hose is less warm but not cold. After some investigation, I thought the heater core might be clogged, so I thought I would use an air compressor to blow out the gunk.
First thing I noticed: when I took the hoses off the water pump and therm housing, no coolant splashed - the hoses were dry, even though I'd just had the Jeep up to operating speed. I went ahead and used the compressor, and got almost nothing out of the core - just a small splash of coolant. I refilled the hoses with fresh coolant (trying to fill the core itself) and put everything back together. When I test drove it, the air coming out of the vents warmed up quite a bit for a little while, and then went back to lukewarm/cool.
Another odd thing I've noticed is that no matter how hot/cold I've gotten the Jeep, my overflow reservoir is always at the same level.
My next thought is that the water pump is bad, but it doesn't overheat - gets up to about 200 degrees and stays there. Granted, it's been averaging about -5 degrees outside here in Alaska lately, but even when it was warmer, it didn't overheat. Do you think my water pump is bad? I don't want to replace that in these temps (I don't have a garage) unless there's a good chance that's the problem. Perhaps a bad water pump means there's no coolant through the core, and thus no heat?
Any help you guys could give would be greatly appreciated.