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Unread 02-17-2014, 01:40 PM   #1
unabashedpraise
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Finicky Heater Issues

Searched and tested many different forum issues/fixes.

Current problem is that at idle the heater puts out luke warm air. At higher rpm's the heat is nice and warm.


-I have a smallish leak in my radiator, upper driver's side. After being driven around town and then left sitting over night we usually have about a 6" diameter wet spot from the coolant leak.
-I keep the overflow tank full, but have to fill it up from the "add" level about every three weeks.
-Have flushed core/radiator in last 6 months, I did hear gurgling from inside cab after system was refilled. I think I burped it properly at the time and don't hear any more gurgling sounds.
-No OBDII codes, no ATC codes.
-Both heater core hoses are nice and hot so I'm at least getting some circulation.
-Blend door shaft turns when the temp control is moved from hot to cold and back again.
-Strong air comes out of the vents and changes from all settings properly.
-Temp gauge works, sits at 195-ish; thermostat changed in last year.
-New rad cap in last 6 mo.
-Water pump changed couple years ago.

-I planned on waiting for warmer weather to repair the radiator. Meanwhile I took a chance and bought some Bars Copper radiator leak seal and put it in. I usually don't mess with this, but was hoping it might hold me for awhile. The issue of luke warm air was happening before the stop leak was added. It's only been a couple of days and haven't seen any change in leaking amounts or in heat from the vents. Same issues before and after.

Would the leak in the radiator be enough to allow air to get trapped in the heater core? Water pump need replaced?

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1998 Grand Cherokee Limited; 5.2 L, 249

Help: Rear left lock doesn't lock using power locks, but will unlock. Any ideas?

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Unread 02-18-2014, 01:05 PM   #2
unabashedpraise
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Now I know forum members aren't THAT busy at work...
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1998 Grand Cherokee Limited; 5.2 L, 249

Help: Rear left lock doesn't lock using power locks, but will unlock. Any ideas?

-Born once, die twice. Born twice, die once.
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Unread 02-19-2014, 07:23 AM   #3
bcbueller
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does the fan speed change while this is happening ?
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Unread 02-19-2014, 09:59 AM   #4
unabashedpraise
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Fan speed normal.
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1998 Grand Cherokee Limited; 5.2 L, 249

Help: Rear left lock doesn't lock using power locks, but will unlock. Any ideas?

-Born once, die twice. Born twice, die once.
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Unread 02-19-2014, 08:24 PM   #5
bcbueller
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i would still suspect your heater core . . i have removed/reinstalled my complete heating system in my 98 and i had similar issues till i guttedd it and reinstalled and now it seems like all is well . sorry thats all i have
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Unread 02-19-2014, 10:39 PM   #6
unabashedpraise
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Did you replace with a new one?
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1998 Grand Cherokee Limited; 5.2 L, 249

Help: Rear left lock doesn't lock using power locks, but will unlock. Any ideas?

-Born once, die twice. Born twice, die once.
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Unread 02-20-2014, 01:04 AM   #7
Uniblurb
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You don't have a pressurized system if you have a leak in your radiator. If coolant can bleed out air can leak in. And if your heater core is clogged that Bars stop-leak will just make it worse. Personally I'd replace your radiator, they aren't all that expensive, and flush the whole system out. Also flush your heater core out separately in both directions using the heater hoses. Good luck!
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Unread 02-21-2014, 09:18 AM   #8
bcbueller
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removed heater core had it sent out flushed and tested it was full of crap that just flushing it regular ( twice) did not work
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Unread 02-21-2014, 09:59 AM   #9
Uniblurb
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Still believe it's worth a shot to flush the heater core before going through the hassle of tearing the whole dash apart to replace it. And while you're in there you might as well replace the AC evaporator which are known to leak/fail, the accumulator (filter/dryer) should also be replaced, evac/recharge the AC system, and it gets real pricey. I've done this repair on both my ZJ and wife's TJ while not wishing it on anybody.

An open cooling system with a leak in the radiator pulling in air may be the root of the problem in my opinion.
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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
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Unread 02-21-2014, 11:53 AM   #10
unabashedpraise
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Last night I drove with no discernable heat. Gotta do something.

This morning while researching my issue I realized that I have never reverse flushed the core. I got everything setup, isolated the core and used hot water and air to flush. I used air first, then hot water, then air, etc. I did get a lot of crud out including this gem. Even after the tenth time I was still getting sediment out. I burped the system and will double check fluids after some driving.

This is about 4" long piece of gasket sealer...
2014-02-21-12.49.29.png

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1998 Grand Cherokee Limited; 5.2 L, 249

Help: Rear left lock doesn't lock using power locks, but will unlock. Any ideas?

-Born once, die twice. Born twice, die once.
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Unread 02-21-2014, 01:24 PM   #11
Uniblurb
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Ahh, looks like a little too much gasket sealer on the thermostat housing or water pump when replaced. If that type of sealer gets in the thermostat area it can also cause the thermostat to not close all the way. Curious if any of the Bars copper particles also came out of the core?
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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 02-21-2014, 02:00 PM   #12
unabashedpraise
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I did not see any large shiny chunks, but a lot of darker pieces. Adobe chunks may have come off the hoses as well. Heat was hot going to work, course it was 56 outside too...
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1998 Grand Cherokee Limited; 5.2 L, 249

Help: Rear left lock doesn't lock using power locks, but will unlock. Any ideas?

-Born once, die twice. Born twice, die once.
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Unread 02-22-2014, 07:05 PM   #13
50notch
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I chased a poor heat temp issue for like a year! My heat output sucked no matter what, idling or driving, flushing heater core, new t stat, even a new water pump. I only replaced the water pump because I was in there replacing my leaky timing cover gasket. Anyway, last month I finally had it with having little heat in the jeep and replaced the heater core and a/c evap core. I think 90% of my issue was that most of the foam that seals all the ducting to the HVAC box had deteriorated to the point that air was just going everywhere. I blew through my heater core with very little resistance. After replacing the cores and all the foam my is hotter than it has been in the 5yrs I've owned the jeep!
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Unread 02-24-2014, 11:32 AM   #14
unabashedpraise
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Heat is much better, in fact while driving it is warmer than it has been in a long while. However, while idling at a stop light it still seems to blow cool air. The stop leak seems to have plugged the small leak in the radiator. I'm still going to get it fixed this summer, but I'm still trying to figure out if this is water pump related or not. This week I'm going to put a flushing agent in the heater core, then flush with air and water again.
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1998 Grand Cherokee Limited; 5.2 L, 249

Help: Rear left lock doesn't lock using power locks, but will unlock. Any ideas?

-Born once, die twice. Born twice, die once.
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