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Unread 04-04-2013, 06:59 PM   #1
Pronounced "Mucky J"
MukYJ's Avatar
1993 YJ Wrangler 
Join Date: Jan 2007
Location: Sultan, WA
Posts: 208
Heater core maybe leaking?

So, after replacing my 2.5 with a new 2.5, I've been having some temperature fluctuations while the engine is warming up - it's behaving exactly like a sticky/slow thermostat, where it will get warmer and warmer until it gets up to about the 240 or 250 mark on the gauge, then it'll drop down to 180 once the thermostat opens up. It slowly builds again, this time it'll get up to about 220 before dropping to about 190, and after that it'll warm back up to 210 and stay there (as it should).

The problem I was having was that when it got to the hottest point, I think it may have revealed a small leak in my heater core - steam pouring from the defroster vents, fluid leaking out the bottom of the jeep, driving with the windows open, and occasionally wiping the inside of the windshield with a paper towel; fun times.

Well I got a new thermostat and radiator cap. I haven't had the time to replace the thermostat yet, but I did replace the cap Tuesday night and I realized the old cap was a 16 psi cap instead of the usual 13 psi. The new cap seems to help stabilize the temperature swings (though I'm still going to do the thermostat this weekend) and the leaking, and what is even more amazing is that the steam from the vents has stopped too, once the fluid that was in the heater box had time to fully evaporate. I think I must have a magic Jeep.

So I guess the question is, could just having the wrong radiator cap with that extra 3 psi have caused the heater core to start leaking? I had the same cap with the old engine, and never had problems with the core leaking. I'm thinking I may have cracked some solder while removing the hoses to pull the engine.

The radiator cap wouldn't have caused the near overheating though, right? That seems like it would be more the job of the thermostat...

~/Garth - 1993 Wrangler S 2.5
{ }|||||||{ } "MukYJ"

Originally Posted by Anticanman View Post
He's right, as soon as you remove the trackbar the fuel rail will arc on the battery, killing you and all the kittens in a ten mile radius.
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Unread 04-04-2013, 09:50 PM   #2
Web Wheeler
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1992 YJ Wrangler 
Join Date: Jan 2013
Location: Cardiff by the Sea - Glamis North, Ca
Posts: 1,255
The heater core is sealed, after the water enters at the fire-wall i don't think there is a way for water to end up in the heater box unless the core has a hole. I just changed mine, it's a PITA but I did mine without unhooking the air-conditioner so I had to do a whole lot of wiggling to get the heater box out, if you don't have A/C it would be a piece of cake.
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Unread 04-05-2013, 01:25 AM   #3
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1991 YJ Wrangler 
Join Date: Apr 2012
Location: hesperia, ca
Posts: 195
I had very similiar symptoms with my 1991 2.5L. I kept getting very small pools of antifreeze on my passenger floor board. I replaced my heater core and found it had a very small leak from one of the vains. It was a very small leak. It is a PITA!!!! I would hate to see the labor cost of having a shop change it for me.
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heater core , leaking coolant , radiator cap , thermostat

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