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Topic Review (Newest First)
10-15-2012 10:54 AM
Heater on and off ?

Hi, I have read this thread and have a related question: Jeep wrangler sport 1999.
Heat works intermittently and doesn't respond to the dials. Sometimes it gets nice and hot and then won't shut off and other times doesn't work at all. Plenty of coolant and no apparent leaks. ??
I really want to fix this myself but am not sure what is going wrong, ideas?
11-30-2010 11:31 PM
mike_the_engineer Also, run the water in the opposite direction that it normally flows. So spray water into the outlet pipe and whatever crud is in there should come out of the inlet pipe.
11-30-2010 10:59 PM
If I held the RPMs up for awhile I'm assuming the outlet hose would also be hot
Yep. In fact, it should be hot at idle if the heat is on.

Perhaps there is a blockage and whenever I ramp up the RPMs it gives the coolant enough pressure to push past the blockage and bring back the heat?
That's exactly what's happening. And like jason said, it's probably your heater core that's clogged. That's a really common problem and you can flush it with a garden hose. Just pop off the two heater hoses where they connect at the firewall and run some water through it. Just be careful when you do that. The core is somewhat delicate and it isn't built to handle a lot of pressure. If you rupture it, you have to take the entire dash out to replace it. Not fun. If all goes well, the entire job shouldn't take more than 15 minutes.

A few tips:

1) Wait until the engine is cool. Getting sprayed with hot antifreeze sucks.

2) When you pull off the hoses, coolant is going to go everywhere. Have a bucket handy.

3) Don't leave used antifreeze laying around. It's highly toxic. Dogs will drink it because it smells sweet, and if they do, they'll die. Painfully. Make sure you clean it up, recycle it properly, blah blah.

Best of luck!
11-30-2010 10:20 PM
jasonwrangler heater core is clogged up, try flush it.
11-30-2010 10:02 PM
MrMiyagi Only residual heat. As soon as I let off the RPM it stops blowing out hot air. Just some more info:

Coolant level is OK

Inlet heater core hose is hot, outlet heater core hose is cold (this is at idle. If I held the RPMs up for awhile I'm assuming the outlet hose would also be hot)

So...this could call for a flush?

I'm not sure how the vacuum system or water pump system works on the jeep. Perhaps there is a blockage and whenever I ramp up the RPMs it gives the coolant enough pressure to push past the blockage and bring back the heat?
11-30-2010 09:49 PM
jasonwrangler once you get heat but the RPM goes below 1k do you get heat?
have you check your coolant level?
11-30-2010 08:46 PM
Heater issue

Hey guys,

Couldnt find a thread that helped me out. I have a 2006 TJ and the heater isn't working correctly. When I let the jeep sit idle and reach operating temperature with the heater on, there is no heat. Only until I start driving and run at RPMs over a grand will the heater kick on. I'm guessing this isn't electrical and has something to do with my vacuum tubing? I checked some of the connections that were easily reachable but didn't want to proceed any futher unless I had someone to back me up that I was going in the right direciton.

Any help?


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