ZJ Heater Core Slight Leak - JeepForum.com
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post #1 of 6 Old 08-19-2019, 11:26 AM Thread Starter
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ZJ Heater Core Slight Leak

I have a 97 ZJ and the heater core has a slight leak.

Everything that I have read indicates that the replacement of the heater core is a bear of a job.

This leads me to think of two different ways to deal with this.

First, tear the dashboard out to get to the heater core and replace it.

Second, use something like K-seal to plug the leak. If I do this should I leave the K-seal in of flush after the leak is repaired.

I want to all the pros and cons.


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1997 ZJ 4.0 L - Upgraded to heavy 93 sway bar
2004 WJ 4.7 L - 2 1/2" lift
2011 KK 3.7 L
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post #2 of 6 Old 08-19-2019, 12:05 PM
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1993 ZJ 
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Getting to the heater core the right way is an involved process. When I did it it took about 6 hours, taking my time, and referring to the Haynes manual. It is not at all difficult. It just takes a while and there are a lot of parts to remove. The Haynes manuals might be a little lacking here and there in general, but the step-by-step for removing the dash is very good. Or at least it is for the 93-95 interior. You do have to discharge and recharge the AC to do it but IMHO it's worth it. I have a vacuum pump and manifold set though so it's not a big deal for me. Reportedly most AC shops will evacuate your system for very little.

As for the heater core, I would get the APDI/PRO version on RockAuto. Based on the pictures, it's the only one that has the tubes brazed to the tank like the OEM core. All the others have an o-ring seal at the tank retained with a crimp. I don't really want to add a potential leak point to the system. Now, that's just my gut; I haven't heard of that style failing so it may be a non-issue.

Some folks (most?) will recommend replacing the evaporator while you're in there. I didn't replace mine on my 93. It looked like it was in good shape. It's still fine now about 5 years later.
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post #3 of 6 Old 08-19-2019, 03:15 PM
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1998 ZJ 
Join Date: May 2018
Location: Ozark
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ZJ Heater Core Slight Leak

Here is the full step by step write up on this replacement. Itís easy to follow and extremely helpful.

Mine has been leaking for a year or so now and I still havenít gotten to it mainly bc itís no longer my daily driver and I live in the Ozarks so I can get away with not using antifreeze for 8-9 months of the year, so I just top off my radiator every week.

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post #4 of 6 Old 08-19-2019, 03:44 PM
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1998 ZJ 
Join Date: May 2018
Location: Ozark
Posts: 99
Iím also putting it off until Iíve bought the following to do at the same time..
-fix blend door (not sure what the issue is yet)
-evap core (you should really consider doing this at the same time too.
-run 8awg line through firewall to the rear end.
-new radio head unit. And running some lines for that as well.
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post #5 of 6 Old 08-19-2019, 04:22 PM
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1997 ZJ 
Join Date: Nov 2014
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There is a shortcut way that doesn't require removing the entire dash. You take off the top and then cut out some of the plastic dash support framing above the heater core. Don't worry, you'll see that the material you cut out doesn't really do much of anything. Also, you cut the tubes and splice in the new heater core with heater hose over the cuts.

Yeah I know this sounds horribly shadetree mechanic, but it's a lot simpler and doesn't lead to a rattling dash or anything. 10 or 12 screws, cut some plastic, cut the aluminum tubes, get 2 pieces of heater hose 2 or 3 inches long and 4 hose clamps and you're done. And if it ever leaks again you can change it in under 30 minutes.

I didn't look at the method posted above to see if that is it, but the shortcut is posted on here. Do a search.
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post #6 of 6 Old 08-19-2019, 07:55 PM
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It takes time. The most issue is the plugs on the passenger side . And be careful with the antenna wire. I just stripped a 97.

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