Heater Core Replacement

[Keyav8r]

Well, I went into the garage today to bleed the brakes and paint the interior of the cab. But, when I looked into the cab I found a puddle of antifreeze in the passenger side floor. Gotta be heater core leaking.

 

I had bought radiator and heater hoses to be changed sometime in the future, but it looks like the future is here. I pulled all the hoses off (made phortos as I went), and pulled the radiator. Surprise - it looks like the PO or the PO once removed replaced the radiator at some point with a double core plastic tank radiator that is in really good shape. And, the PO actually did change the water pump as he said he did.

 

Also found the rubber just starting to poke out on the crank pulley/vibration dampener. Another project for sooner than I planned - like right now. Guess I'll go ahead and install the new timing gears, chain, seal and gasket while I have the radiator out.

 

I have pulled the dash out but can't see how to get to the heater core. Has anyone done a thread on changing a heater core? If so, could someone kindly point me to it? I tried searching for "changing heater core", "heater core replacement", etc. but couldn't find a detailed thread. I sort of remember reading something about some bolts on the firewall, but I don't want ot start randomly un-bolting things assuming that I will eventually find the majic bolt.

 

Being one of them dumb ole Southern boys, I work better with pictures. Anybody got a lead on this?

[Backdraft]

The entire HVAC box will need to be pulled to get at the heater core. You are correct in the location of the mounting bolts. There are five of them. One near the passenger side inner fender. Two almost directly underneath the heater and ac lines going into the box from the engine bay (these two wil be one on top of the other with about a 6 to 8 inch gap in between them). And two more one above the other almost directly behind the engine its self. They will be just to the passenger side off center from behind the head/block. These will all be nuts that you remove ( 10mm IIRC). The studs are formed into the HVAC box its self. You will also have to remove the heater hoses from the heater core as well as the AC lines from the evaporator if applicable. There are also a vacuum line or two that needs to come loose. Should be right by the heater hose connections. After that, it pulls straight out from the inside of the cab. Once its out, theres about a hundred little screws that hold the top and bottom halfs of the HVAC box together. Remove them, pop the top half off and you should be able to access the heater core for replacement. Assembly is simply in reverse order. Sorry, didnt have any pictures, but maybe i droned on with enough details to paint a picture. Good luck

[Keyav8r]

Backdraft - Thanks for the assistance! That's what really like about this forum. There's always someone who knows whatever is needed.

 

I remember seeing about three of the five studs you listed - the two behind the engine and one of the two under the heater lines. I've got the heater hoses off already. The AC isn't working so pulling the evaporator lines won't be a problem. I may get the evaporator checked for leaks before I re- install it. May as well disconnect the condenser and get it checked, too.

 

Again, many thanks for the info.

[Automan2164]

I'll add something to what has been said already... The five or so nuts/studs on the firewall - Don't get down if you can't stop the stud from spinning. If you just end up turning the whole assembly, it's fine. The stud isn't molded in, it threads in. If you spin the nut/stud as a unit, it will just be unscrewing the box on the other side. Then, after you remove the box, you will be able to grab the stud from the interior and get the nut off.

 

Rob

[Keyav8r]

Thanks, again. One thing I didn't mention and haven't seen on the forum - the fan thermostat/switch is in a fitting in the lower radiator hose, not in the radiator itself. The fitting has hose connections on both ends, about 3" long, and a boss in the middle to accept the thermostat/ switch. It looks like about an inch was cut out of the hose and the fitting inserted and clamped with screw type hose clamps.

I'm assuming the radiator was not '88 MJ specific.

[Backdraft]

Concerning the AC, If you have the lines unhooked and open to the atmosphere for an extended period of time, a new reciever/dryer may be in order. It is filled with a dessicant material and is very moisture sensitive.

 

For that temp switch. Its not OEM. Check the drivers side tank of your radiator. Just above the radiator hose, there should be a bung about an inch and a half to two inch diameter with a plug screwed into it. The plug has two wires coming off of it. That is a temp switch. If its not there, or no bung is present, it is probably a replacement radiator and that fitting with the boss is most likely an improvisation to put a temp switch back in service.

[Keyav8r]

Took another look at the radiator. There is what looks like a bung with a socket head plastic plug just above the lower hose bung. It appears to be the correct size for the temp switch. I believe the temp switch itself is OEM because it has the correct connector.

I'm going to GENTLY try to remove the plug and, if successful, put the switch back where it belongs. If the. Plug doesn't come out easily, I'll leave things as they are - don't want to buy another radiator right now.

The other thing I'm considering is adding a fill fitting in the upper hose as Pete did on his MJ. Keep the closed system. Just make it easier to fill and burp.

[skidoo_j]

I'm about to tackle this same issue, but was wondering if the entire dash is required to be removed or if the FSM is correct and I just have to remove the lower dash panel and the center console?

[MancheKid86]

Filling/burping a closed system is easier than it is made out to be,

Remove the upper rad hose going to the Tstat hold that hose comepletly straight up in the air,

FiLling the hose to the to the rim,

This will gravity feed/purge the entire system,

Once it is completley purged the anti freeze will come out of the tast fitting where the rad hose goes on,

 

Clamp the hose back on, fill up the overflow resivoir and you are done.

[Keyav8r]

Skidooj - after pulling my dash and looking at the HVAC module I don't see how you could get it out otherwise. Doesn't look like there would be enough room to pull the assembly back far enough to get the studs out of the firewall and then slide it out under the dash.

You've also got the connections for the heater core that project through the firewall and, in my case, the evaporator connections.

[skidoo_j]

Skidooj - after pulling my dash and looking at the HVAC module I don't see how you could get it out otherwise. Doesn't look like there would be enough room to pull the assembly back far enough to get the studs out of the firewall and then slide it out under the dash.

You've also got the connections for the heater core that project through the firewall and, in my case, the evaporator connections.

 

that's horrible.... I've never understood why they make wearable parts so damn hard to replace. It's even worse on new vehicles. spent almost 8 hours on my buddies 95 ranger replacing the heater core, had to pull the whole dash. the 93 ranger was a 30 minute replacement.

[Keyav8r]

Promotes dealer service business and dealer mechanic job security.

[Keyav8r]

Put a hex wrench in the plastic plug in the bung on my radiator and it came out smoothly. Unscrewed the fan switch from the fitting that had been spliced into the lower radiator hose and it screwed right into bung. Don't know why the PO didn't do that. Now I can put it back together the way Jeep intended (after I change the heater core).

I took photos of the heater hose arrangement so I may actually be able to put it back together right.