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Old 12-29-2010, 11:27 AM
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Question TJ heater problems

Hi all,

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.
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Old 12-29-2010, 11:50 AM   #2
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heater pump is unlikely bad because youre not over heating. as for why the coolant level does not change it could be that its so cold the engine coolant is running constantly in closed loop.
flushing out heater core you better use a water hose and back flush.

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Old 12-29-2010, 11:59 AM   #3
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X2 on backflushing the core with water. I need to do the same thing to mine. Might do that today in fact. My heater isn't running as hot as I would like.
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Old 12-29-2010, 12:30 PM
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Thanks, guys. Guess it'll have to wait until spring, since I don't have access to a garden hose until everything thaws. Maybe I'll take it to a Qwik-e-lube and see about a cooling system flush.
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Old 12-29-2010, 04:48 PM   #5
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i ve been in this same problem a friend of mine who owns a garage says these jeeps some how come up with air pockets.we used a air bleeder from snapon it worked you have to get the filler point higher than the heater core.u can buy the adater at the parts stores to fill it witch will let the air out while u fill it.
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Old 11-15-2014, 08:53 PM   #6
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We have a problem where the passenger side gets all the heat, while the driver suffers in the cold. Sounds like an actuator door not opening properly?

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