No Heat! Schizophrenic Symptoms '00 XJ

little to no heat blowing in wifes daily drive 2000 xj
here is whats happening....

took a highway trip the other day and the heat seemed to go out.
10F outside - heater blowing COLD air

drive around yesterday 35F outside and i get some warm heat (still not what i get out of my other xj)

heat controls work - they go from defrost to vent to floor and there is a change in hot to cold when i turn the knob. new thermostat, water pump and radiator

what do i need to do to check this all out?

check coolant level?
check heater hoses that BOTH are hot?
maybe flush heater core?
burp the system, maybe air in it?

any othe suggestions? this seems to be a wierd on/off problem right now.

dumbagain said:

what do i need to do to check this all out?

check coolant level?
check heater hoses that BOTH are hot?
maybe flush heater core?
burp the system, maybe air in it?

any othe suggestions? this seems to be a wierd on/off problem right now.

Click to expand...

Start with those four things. On the plus side, you don't have a heater valve to worry about.

When you do the flush, use the 8-hour stuff, not the 'quick' flushes. It's OK to drive around with it in there over the course of a few days and does a much better job than the fast flushes. Be sure to both reverse- and forward-flush the core, BTW.

Cab heat is simply a byproduct of engine heat. What is the coolant temp gauge in the dash reading? The target there is 200-210. If that is good, that eliminates a few things.

Of course, coolant level must be verified. And because you have a 2000, with the infamous 0331 cylinder head which can crack, keeping a close eye on that should be second nature to you by now, because coolant loss is the #1 symptom of a cracked 0331 cylinder head.

You very possibly have a partially clogged heater core. You could try flushing both inlet / outlet with garden hose pressure. If that doesn't help, using CLR can be helpful. It is worth a try before tearing apart the dash to replace the heater core. Below is a link to a video showing the process. I have actually used this technique a couple of times with some success.

Good luck and be sure to check back in to update us.

http://www.youtube.com/watch?v=dcL_0TWeZJY&feature=channel

forgot to mention the jeep gets up to and stays at 210ish operating temp with no prob