Cummins Diesel Forum banner

heater core replacement

2004 Views 10 Replies 6 Participants Last post by  Brian01
OK, I've been reading the forums for a while now with regard to changing out the heater core, now that it's getting cold the time has come to change it out. I have the fog/mist coming out of the vents and the top radiator hose is stone cold even with the temp gauge reading 190* so i think its time to swap it out. Pass side floor is dry but if I turn on the defroster the windshield gets coated with antifreeze film. I was wondering if this job has already been done on my truck? I'm the third owner and it has 140k its a 1997 2500 4x4. The reason I ask is that I already have heater hose running from the engine hard lines directly through the firewall and I wasn't sure if this indicates that someone has already been in there? I thought the heater core hard lines would have come through the firewall and been connected with heater hose under the hood from the core lines to the engine lines?
1 - 4 of 11 Posts
The heater core lines are stubbies that just stick out the firewall a couple inches. When the heater hoses are connected they slide all the way up, giving the appearance that they go through the firewall. If your core is leaking it is an indication of really poor maintenance being done by the prior owners. My heater core is the original. I suspect your radiator will be leaking soon also.

I'm curious about the top radiator hose being cold. You are talking about the one into the radiator, right?
I am not sure, but here is a writeup on how to change the dash which is needed for a heater core replacement.

I found that removing the steering column made it is a lot easier when I took a dash from a junk truck.
A lot of that stuff is not required (like removing the instrument cluster) to replace the heater core. The FSM has you evacuate the A/C, again not required. In addition, there are a few things not in that link that do have to be done.
It is not necessary to break the old pipes off or cut the new ones. The plenum can be unbolted (bolts are in the engine compartment) and slid back. If you have access to the Turbo Diesel Register issue 59, page 90 has a picture and instructions. If not, this is a pretty good write up. My experience replacing the heater core in my 2001

There are also instructions in the FSM. (WHAT??? read the repair manual????. What a concept!!!)
It sounds like your t-stat is stuck open, possibly missing. I recommend a genuine Cummins, the ones out of parts stores don't seem to work well, judging by several dozen threads. You will get better fuel mileage if the thermostat works correctly.
1 - 4 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.