Heater core exploded

Rock Toy

TJ Enthusiast
Joined
May 3, 2020
Messages
251
Location
San Francisco
This is not my day. I just finished doing some work on the TJ (O2 sensors) and took it for a spin around the neighborhood. Motor got warmed up and then as I came to a stop sign, the heater code blew up. Keep in mind that I just replaced the heater core no more than 50 miles ago. Anyone have any thoughts as to why that might have happened? I bought the TJ with a blown core so I'm starting to think that the problem is in the return line. Maybe plugged at the water pump? I can't imagine that the new core just blew out without being overpressurized. Regardless, I rerouted the inlet to the outlet on the pump and everything works fine again. Jeep runs great and not oveheating.
 
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Everything else appears to be fine. No other leaks anywhere and the temp gauge (stock one in the dash) is reading right down the middle at 210.
 
It's not a blockage by the way. The water pump is a centrifugal pump just like a vacuum cleaner. When flow is reduced pressure is reduced. Just like when you plug a vacuum cleaner the motor speeds up instead of slowing down.
 
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This is not my day. I just finished doing some work on the TJ (O2 sensors) and took it for a spin around the neighborhood. Motor got warmed up and then as I came to a stop sign, the heater code blew up. Keep in mind that I just replaced the heater core no more than 50 miles ago. Anyone have any thoughts as to why that might have happened? I bought the TJ with a blown core so I'm starting to think that the problem is in the return line. Maybe plugged at the water pump? I can't imagine that the new core just blew out without being overpressurized. Regardless, I rerouted the inlet to the outlet on the pump and everything works fine again. Jeep runs great and not oveheating.
If the water pump were capable of generating enough pressure to blow up the heater core, then it would also be able to blow up the rubber hose you are now directing the pressure through. You have something else going on.

That and it isn't a positive displacement pump so it can't really produce those pressures as stated above.
 
Right. I can’t imagine what it is then. If When I was filling the radiator with the motor off after the core blew, the water would exit through the overflow valve out of the heater box. So I’m sure that the heater core is done. But then when I reroutes the line, everything runs great and the motor appears to maintain temperature (so not a head gasket). I assumed that the return to the water pump might be bad because it would explain why the breakage point would be the heater core but maybe the radiator cap is the culprit. I definitely down see the overflow canister filling up. No action at all in there...
 
Sometimes new parts are defective and just fail right away. Unfortunately, that happens. Replace the cap no matter what, they are cheap.

You’re probably right. Kind of sucks that I have to redo the heater core though. Involves pulling the entire dash and “speaker holder” 🤣. Maybe a good opportunity to weld in some diagonals and re powdercoat it.

Off to pick up a new cap then.
 
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Right. I can’t imagine what it is then. If When I was filling the radiator with the motor off after the core blew, the water would exit through the overflow valve out of the heater box. So I’m sure that the heater core is done. But then when I reroutes the line, everything runs great and the motor appears to maintain temperature (so not a head gasket). I assumed that the return to the water pump might be bad because it would explain why the breakage point would be the heater core but maybe the radiator cap is the culprit. I definitely down see the overflow canister filling up. No action at all in there...
Also doubt the radiator cap is the issue. If it was, the core on the radiator would also have blown out.
 
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My experience with Murray products leads me to avoid pretty much everything they sell. The parent company Briggs & Stratton just filed for protection.
 
Lol i dont think id be able to go back and ask for $60 back without throwing it into someones face after dumping 8 hours into that project.
Sucks for sure. On a positive note, now you can insulate a firewall if you have not done so already. We have a thread on this somewhere. Somewhere deep inside i wish mine would explode to give me another reason to take it apart and insulate everything in there, still kicking myself for not doing that when had a chance.

I just finished replacing rear main seal for the 3rd time, just to discover that it was a new valve cove leaking all this time. Just smile, grab a beer, and have a good laugh :D
 
Lol i dont think id be able to go back and ask for $60 back without throwing it into someones face after dumping 8 hours into that project.
Sucks for sure. On a positive note, now you can insulate a firewall if you have not done so already. We have a thread on this somewhere. Somewhere deep inside i wish mine would explode to give me another reason to take it apart and insulate everything in there, still kicking myself for not doing that when had a chance.

I just finished replacing rear main seal for the 3rd time, just to discover that it was a new valve cove leaking all this time. Just smile, grab a beer, and have a good laugh :D

You can be the go-to RMS guy now. LOL