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Discussion Starter · #1 ·
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?
 

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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?
 

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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.

http://www.cumminsforum.com/forum/94-98-chassis/285351-94-98-5-dash-replacement.html
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.
 

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My .02¢… just replaced my heater core bout a week or two. Its a job no doubt. But not as bad as everyone let's on... here's what all I done. Pop the dash bezel off. Took off battery terminals. Took airbag out. Dropped steering sector. Popped off the kick panels, near them on both passenger and driver side there is a bolt that holds dash up. Loosen them.. take bolts out along top of dash, near windshield, took cup holder and shifter cover loose. pull dash forward. Took little brackets off that hold core and core lines down. Core itself will not lift out with the tubes going through firewall...here's what I done...easy fix...take the rubber lines off under hood of course. Just bent the core tubes until the broke off right next to the core...pulled it out.no problem... on the new one I took a hacksaw n cut the lines down tojust a few inches. We t to auto store n bought new hose. 4 ft is plenty. Drip the new core in and put brackets back on. Tear out the little plastic piece that the lines go through on firewall...run the new hoses through and put em up on the core lines...clamp and put it all back together...
 

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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!!!)
 

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Discussion Starter · #7 ·
Thanks for the replies, I will get into it this weekend. GAmes, the top radiator hose is the one I was talking about, I suspect the T-stat is not working properly or not at all? the engine never overheats and seems to run fine. I will most likely do a pressure test on the system just to see if anything is out of spec.
I have a 4BT in an F-150 and had to take the fan right off the engine since it never got above 160* without the fan even in July / August I barley break 180 even in stop and go traffic, without the fan I get it up to operating temp and it seems to run better at 180.
 

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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.
 

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I too replaced my heater core without cutting the new heater core inlet/outlet tubes. I did cut the tubes on the old heater core just to make it easier to remove but the new heater core had adjustable tubes and it was a bit harder to put in but it can be done. I got my heater core with adjustable tubes from NAPA.
If you have a cracked dash board this would be the time to change it too.
 
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