98 ZJ 5.9 Troubleshooting cold heater air - JeepForum.com
 
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post #1 of 13 Old 10-19-2016, 03:15 PM Thread Starter
DrReaper
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98 ZJ 5.9 Troubleshooting cold heater air

98 ZJ blowing cold air when heat is turned up

It's starting to get cooler here in Idaho. Looking a 40F next week. It's my first winter so I would like to have the jeep get warm in the mornings.

I recently replaced the blower motor regulator and the blower motor to fix a vampiric battery draw. The air really blows well now with the new motor. However, it never gets hot. If i set the system to 85 it doesn't go past 65.

I flushed the heater core with the garden hose and clear water came out. No debris as far as I could tell. I back flushed it as well.

I tested the hose temps at the firewall in the engine well and they are both at 114

Not sure what to look for next. I did look up the system in the Chilton guide and it says there is a "Heater Water Control Valve" I don't see one in the engine compartment.

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post #2 of 13 Old 10-19-2016, 09:15 PM Thread Starter
DrReaper
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Removed the blend motor and was able to move the door by hand. No difference. I connected power to the motor and tried the controls and the motor doesn't move. Strange it may be broken but not the problem.
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post #3 of 13 Old 10-20-2016, 12:25 AM
Zilliver
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Did you bleed the cooling system correctly?

´95 Grand Cherokee 5.2
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post #4 of 13 Old 10-20-2016, 05:05 AM
jeepjeepster
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Are you sure you removed the blend door for the temp and not the position door?

The blend door for the temp is known to have issues with the little gears internally snapping, so it cant move the door. Removing it like you did and manually moving the door would bypass that, of course.

Have you felt of the heater hoses to see if both are hot?

1994 ZJ-I6 w/216,000 mi
1998 ZJ 5.9 w/65,155 mi Slate Black
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post #5 of 13 Old 10-20-2016, 07:13 AM
Timo_90xj
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Wait.. hose temps at firewall are only 114°F? Coolant from the engine goes to the heater core, then back to water pump, then to radiator. With the engine at operating temp (~200-210°F), both of the hoses should be way hotter than 114°F.

What is your engine operating temp? Does your engine stay at operating temp and has no temp creep in slow traffic/ idling? Are sure your water pump is in good condition?

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #6 of 13 Old 10-20-2016, 02:20 PM Thread Starter
DrReaper
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I backed flushed it again this time with a better connection. Did not help. I did get the blend door motor to actuate so I reinstalled it. This is the motor under the glove box next to the hump. Still no heat.

I am heating the engine by letting it idle in my driveway. It's running about 190. I am testing temperature with a Harbor freight laser temp gauge. Shooting the hoses with the laser.

I am going to drive it a couple of hours tomorrow morning. Will that be enough to burp it if it needs it?
Not sure what to do next.
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post #7 of 13 Old 10-20-2016, 05:53 PM
Uniblurb
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Have you done a self-diagnostic test on your ATC panel to see if it's throwing any codes? It should if you're having motor/door problems.

Here's a real good post with photos showing a cracked nylon gear in the blend door motor.

http://www.jeepforum.com/forum/f13/z.../#post14155615

It's my understanding the coupling between the door shaft and motor can also crack if there is one on your 98.

Typically you can't get air out of the cooling system by just driving it. It takes 3 heat-up/cool-down cycles according to the FSM.

Some still have to bleed the air out of the system by having the front end higher on an incline or jacks/stands while running it with the cap off starting with a cool engine.

Some of the XJ's have the "Heater water control valve" on the heater hose near the firewall for shutting coolant off to the core. But ZJ's do not have this valve and coolant flows through the core anytime the engine/water pump is running.

Agree with Timo and you best get it hotter since temps should be way above 114F at the heater hoses at the firewall. Good luck.

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post #8 of 13 Old 10-27-2016, 12:46 PM Thread Starter
DrReaper
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New update: When the system is set to defrost or defrost and interior and the motor is running and hot. I get heat for maybe a few seconds. Then it goes cold.

Removed a couple of hoses to try to figure this out. They were not clogged. Had to cut one off because it would not break free. Still looking for the answer.
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post #9 of 13 Old 10-27-2016, 02:58 PM
GOLDWING
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Get one of these at your local parts store and install it in the return line from your heater core. connect a couple of feet of garden hose to it and connect a clean transmission funnel to that. Hang the funnel off of the hood and start the engine. Add coolant until you can see it in the funnel and keep the coolant level up until the engine reaches operating temperature. All the air should escape the through high point. Shut off the engine and carefully lift the flush tee up as you pour the excess coolant from the funnel and hose into a drain pan. Disconnect the hose and put the flush tee cap on. Bob's your uncle!

Be very careful of hot coolant and moving parts. Eye protection, heavy rubber gloves and an assistant are recommended.
GW

2 '98 4.0 ZJs
Hers is stock, mine, OME shocks, BB, Aussie, 2x6 sliders, 31s, etc.
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post #10 of 13 Old 10-27-2016, 06:25 PM Thread Starter
DrReaper
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I do have an Uncle named Bob so I will try this before I disassemble the dash.
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post #11 of 13 Old 10-27-2016, 06:38 PM
StPaul59
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A radiator funnel is gold when it comes to burping the system. They might be $30 . If there's a lot of air in the hoses, just driving it wont do much.
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post #12 of 13 Old 10-28-2016, 04:30 PM
AVR2
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I should have got one of those spill-free funnels. I used to burp my ZJ by running the engine with the rad cap off until it stopped spitting coolant everywhere. It always worked, but it made one hell of a mess.
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post #13 of 13 Old 10-30-2016, 04:51 AM
coralman
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They work very well. I am putting a tee in mine now that the block drain is finally free to turn.

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Originally Posted by HighLonesome
lol...if life is as a simple as a 5.9 making you happy, I'd say go ahead and buy it on impulse. ZJs are the way of Zen. Wax on, wax off
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