Jeep XJ/MJ Heater Core Replacement
Installing a new Jeep MJ/XJ heater core without going crazy
Jake HeadleeWriter
If you haven’t figured it out yet, we’re about to cover the replacement of a heater core. Our subject is a ’89 Jeep MJ Comanche, but the steps are basically the same for an XJ Cherokee of similar vintage. This Comanche had a rough life, and it was time to bring it back to its former glory. The heater core was shot, but as Jeep stopped making the original part some time ago, Crown Automotive had stepped up to the plate and made a replacement. Crown has been building quality replacement parts for Jeep vehicles for decades, even going so far as to use OE part numbers to make finding and purchasing them even easier.
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A minor amount of knuckle skin was shed, and a few not-safe-for-work words were said, but we got through it. While doing so, we also attempted some of the so-called “quick fix” ways to replace the heater core in an XJ or MJ. Often, the quick fixes drew us in because we wanted to get back on the trail. Unfortunately, though, some short cuts can lead to more garage time than if it was done by the book. Here’s what we learned.
First, we attempted to take the box apart without removing the dash at all. All of the HVAC boxes used in the XJ and MJ Jeeps are two piece, so internal parts can be replaced, but some are a allegedly a design that allows you to remove the bottom portion of the box without taking the dash assembly out. We learned this was a no-go. Next, we tried doing a partial pull of the dash, unbolting it, leaving most wires connected, and positioning it out of the way so the heater box could be removed worked with some finagling, but this took longer than having taken the few extra steps to completely remove the entire dash.
As tedious as it was, pulling the dash was not that difficult. Lots of small hardware held it in, lots of wires snake through it, but it is entirely doable. The process took about four hours, with a short lunch break in the middle. Follow along as we go through the installation of the new heater core.
