Coolant leak when engine is almost up to temp

toximus

toximus

I live in my Jeep
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I've had a coolant smell that I can't identify the location of when the engine is at 170F, about 30 seconds away from getting up to temp of 210F. I suppose it's possible that the temp gauge is lagging slightly and the smell is happening when the thermostat opens.

I can smell it inside the Jeep pretty strong at first and then it fades to the point of disappearing about 10 minutes later.

The radiator and overflow bottle are still full and I can't identify any drips. There's no drips overnight either. When I turn on the HVAC fan the smell goes away (bringing in fresh air).

I suspect a loose gasket someplace between different types of metal that weeps when the pressure surges from the thermotat opens and once both pieces of metal expand from the heat the gap closes back up.

Any ideas?
 
Well, I'm not a TJ expert by any means, but after I redid the cooling system last year I had the same symptom for about 3 weeks. It eventually went away, and I chalked it up to the significant amount of spillage from flushing the block, spilling some coolant out of the filler neck and down into the fins, etc... I made 2 trips to the car wash to spray everything down with a pressure washer. I was all over it like a hawk but never did find a leak, to this date she's GTG. I used factory everything except for the hoses.

You're probably just a nervous nelly from having poured an unbelievable amount of your soul into this build over the past however many years. I know I would be! The build thread's fantastic BTW.
 
I was thinking heater core, but when mine was going out I smelled it at initial startup if I had the fan on.
 
qslim said:
Well, I'm not a TJ expert by any means, but after I redid the cooling system last year I had the same symptom for about 3 weeks. It eventually went away, and I chalked it up to the significant amount of spillage from flushing the block, spilling some coolant out of the filler neck and down into the fins, etc... I made 2 trips to the car wash to spray everything down with a pressure washer. I was all over it like a hawk but never did find a leak, to this date she's GTG. I used factory everything except for the hoses.

You're probably just a nervous nelly from having poured an unbelievable amount of your soul into this build over the past however many years. I know I would be! The build thread's fantastic BTW.
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Unfortunately this is my wife's Jeep. I last changed the antifreeze about 3 months ago. We have been getting more rain lately so maybe that's reconstituting a pocket of antifreeze that laid dormant in the engine bay?

I'm glad you've been enjoying my build. It's not quite driving yet, but soon!
 
Since you smell it in the cab, my #1 suspect is the heater core. But if you don't see any measurable fluid loss, it's probably not worth worrying about.

I had a similar experience with my '05. I was sure it was the heater core since there seemed to be nothing else it could be. All hoses and the radiator had been replaced and there were no visible signs of a leak anywhere. As with your experience, there was almost no measurable fluid loss.

I got a new OEM heater core (made in France!). Had the A/C evacuated, removed the steering column, the entire dashboard, and the HVAC box. It was obvious the heater core had been leaking but it was a very minor leak. In my Jeep, the heater core is made like the radiator. It has an aluminum core with at least 1 plastic tank. It might have plastic pieces on both ends but I can't recall for sure. It looked like the original heater core was leaking where the plastic tank mates to the aluminum core.

I put everything back together, got the A/C recharged. And I still smell antifreeze sometimes.

My theory is that some OEM heater cores leak even when brand new. I expect if I took it all apart again, it would look just like the original core that I replaced, leaking a small amount, sometimes, where the plastic tank mates to the aluminum core.
 
I suspect that it's the heater core. It's getting better as it's colder outside. I suspect that the mating surfaces are heating up slower and not allowing the weep as it gets to temp.

I have a feeling that a previous owner had run leak stop (due to junk floating in the coolant) and this is probably why... I probably loosened it when I did coolant flushes (which I did only because I didn't know the history).

I ordered a new mopar heater core but I'm going to wait until it's warm next summer to do the work. I don't like working with coolant when it's freezing out... Even in the heated garage.
 
yep. That's heater core. What year is your TJ?

I can guide you if you are of '02 vintage or newer.

"I have passed through many births" - Buddha
 
this is likely what your heater core looks like...

IMG_0675.jpg
 
It's an 05. I haven't removed a dash before, but I feel like I can handle the job. Any other parts needed beside the core itself?

I haven't noticed any coolant on the floor yet but there is some other leak happening during heavy rain and the cowl is clear (I've even dumped 5 gallon buckets of water and can't reproduce it.).
 
toximus said:
It's an 05. I haven't removed a dash before, but I feel like I can handle the job. Any other parts needed beside the core itself?

I haven't noticed any coolant on the floor yet but there is some other leak happening during heavy rain and the cowl is clear (I've even dumped 5 gallon buckets of water and can't reproduce it.).
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It won’t leak on the floor. The housing will keep it contained. It’s a big job but not difficult. The hardest part for me was the nut holding the drain under the cowl. Other than that, pretty straightforward. There’s a damn good video of a guy doing this. Will post it.

You won’t need anything but the exchanger. However, it’s a good time to do the “while you’re in there” stuff. Like replacing the fan resistor.

If you have AC, you’ll need a shop to drain it.
 
I back the claims of the heater core. My YJ had a small enough leak that the coolant simply dried outside of the heater core once it seeped out. Never noticed any leaks or coolant loss but the smell was apparent in the cabin. After I replaced the core the smell was gone, and holy hell did I quickly realize what I had been missing in terms of heat!
 
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Jamison C said:
I back the claims of the heater core. My YJ had a small enough leak that the coolant simply dried outside of the heater core once it seeped out. Never noticed any leaks or coolant loss but the smell was apparent in the cabin. After I replaced the core the smell was gone, and holy hell did I quickly realize what I had been missing in terms of heat!
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This is the first winter in 3 years that I haven't gagged when turning the heat on.

This is the video you need:

If this guy can do it mostly one-handed, you can too!

 
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