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Bad heater core or something else?

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Old Jan 6, 2026 | 07:22 PM
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Default Bad heater core or something else?

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Hey guys. About to finish putting in the vinyl flooring and what not. Had the D1 up on some foot tall ramps while finishing patching the floor. I noticed there was some coolant underneath the vehicle, then I noticed there was some all the way back under the rear differential. Still assumed a small line leak or something. Opened it up today and the entire floorboard was also full leaking from the firewall area. Is this a heater core? It’s been on those ramps about 2 months. Not sure if I need to pull the dash out now and fix that or try something else. I just had the dash out and if I pull it out it’ll need replacing as the radio mount broke and it’s barely in as it is. I’m starting to get frustrated with this build after dumping 7k into it and it’s not even road worthy yet.




suspension was ordered tonight. +2 inch heavy duty TF

TIA!
 
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Old Jan 6, 2026 | 11:33 PM
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Bummer. Maybe delete the heater core to deal with it later at your convenience.
 
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Old Jan 7, 2026 | 06:06 AM
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Originally Posted by JohnZo
Bummer. Maybe delete the heater core to deal with it later at your convenience.
Is this most likely a heater core problem? I’ve never replaced a heater core on any vehicle but that was my first assumption.
 
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Old Jan 7, 2026 | 06:52 AM
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If anyone has an entire dash assembly in the southeast US and sees this please let me know. Starting to get very frustrated with this damn thing. I got the entire dash out and re wired a few months ago, and one of the blend door cables was snagged on something and I had to take it all back apart and I couldn’t figure out what it was hooked on. Figured I’d just deal with no AC on one side. Then I got it all back together.

When I took everything out to take the dash out the first time, the console exploded so I drove to Georgia this sat to get a new one. When I was putting the radio bezel back in after a full re wire, the radio bezel mounts blew out in the back of the dash when I so much as breathed on them ( in the back of the dash that mount to the firewall )



Starting to get really annoyed here and I’m almost 10k into this ****ing thing. I want to see it finished and back on the road, but even then it won’t have a working radio. BIG SIGH. If anyone is in the southeastern United States and would be willing to come up to TN for a weekend and help me with the dash and wiring for the radio and heater core I would appreciate that too. I’ve got nobody to help and I need an extra set of hands.
 
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Old Jan 7, 2026 | 10:08 AM
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I'm feeling your pain. It's not easy to get everything perfect. Maybe just start driving it as soon as you can, so not just dumping cash in with no fun. Driving also helps prioritize work that is actually needed (voice of past experiences) vs work that we think we need.

So, the only way to get engine coolant inside the cab is the heater core and pipes. Could delete the heater core, bypassing pipes in the engine bay temporarily. Make sure that the leak is actually coolant and not rain water first.
 
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Old Jan 7, 2026 | 10:17 AM
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Originally Posted by JohnZo
I'm feeling your pain. It's not easy to get everything perfect. Maybe just start driving it as soon as you can, so not just dumping cash in with no fun. Driving also helps prioritize work that is actually needed (voice of past experiences) vs work that we think we need.

So, the only way to get engine coolant inside the cab is the heater core and pipes. Could delete the heater core, bypassing pipes in the engine bay temporarily. Make sure that the leak is actually coolant and not rain water first.
o it’s coolant alright. Bright green, and it’s been parked inside for a year.

Yes, I went ahead and ordered suspension so I can get it somewhat on the road.
 
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Old Jan 7, 2026 | 01:13 PM
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Have you ruled out a leaking hose clamp/hose...which could potentially spray towards the firewall? Probably not the problem, but stranger things have happened

 
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Old Jan 7, 2026 | 01:27 PM
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Originally Posted by Mark G
Have you ruled out a leaking hose clamp/hose...which could potentially spray towards the firewall? Probably not the problem, but stranger things have happened

I am planning on looking this afternoon. I can’t seem to find a great schematic or picture online of where I am looking for the heater core valve or inlets near the firewall for hoses and clamps. Any suggestions will be appreciated, and pictures if you have them! Lol
 
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Old Jan 7, 2026 | 04:15 PM
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Heater hoses are on the L. side of the engine compartment, above the valve cover on the L side of the engine (as you look at the engine compartment). They're black hoses. You shouldn't have trouble finding them. If a clamp is loose, broke or hose cracked or split then it "could" potentially shoot water into the cabin. May be the heater core, but for sure you want to rule out something simple like a bad/loose hose/clamp. Let us know what it turns out to be. Stop leak is tempting but not a good idea.


 

Last edited by Mark G; Jan 7, 2026 at 04:16 PM.
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Old Jan 7, 2026 | 05:58 PM
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Originally Posted by Mark G
Heater hoses are on the L. side of the engine compartment, above the valve cover on the L side of the engine (as you look at the engine compartment). They're black hoses. You shouldn't have trouble finding them. If a clamp is loose, broke or hose cracked or split then it "could" potentially shoot water into the cabin. May be the heater core, but for sure you want to rule out something simple like a bad/loose hose/clamp. Let us know what it turns out to be. Stop leak is tempting but not a good idea.


Mark, the two hoses going into the heater core are both wet, well, they have been very recently. I can see where they’ve been wet, and they still had some moisture on them. I’m tempted to change them both before digging into the dash again. They aren’t very tight either. I wonder if the thing sitting in a field for a decade and drying up has caused this. Now that I had it on an angle there was probably pressure around that area and it just seeped out. I will go and get some new hoses and new clamps and try that before I dig into the dash.

I will post a picture tomorrow or later tonight to ensure I am looking at the right thing if you don’t mind to verify!
 
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