Coolant from A/C condensation drain tube


New Member
Nov 10, 2018
I've been using this forum for quite a while as it's far superior to all the others out there. So far, I've been able to find any answers I was looking for by making use of existing threads. But now I've encountered a somewhat odd problem, so I decided to register and finally contribute something. (Maybe.) The page to create a profile isn't working for me at the moment, so I'll just give you the details on my particular Jeep and worry about the profile later. 2005 TJ (Sport) with 4.0 I6, automatic.

Here's the issue, I'll try to give all the relevant details up front: On Thursday I drove to work, it's about 30 miles mostly on the highway. I didn't notice anything unusual during the trip. I had the heater on high for most of the trip but had turned it off by the time I arrived. I pulled over to check in at the guard shack but left the Jeep running. When I got back in and began driving again, the "check gauges" light and tone went off, at which point I noticed the temp gauge indicating very hot. It wasn't pegged all the way over to the right, but pretty close. I pulled over and shut the engine off. I popped the hood, checked for coolant leaks there, checked the reservoir (it was low but not empty), checked underneath for leaks, but found nothing. I started it back up and turned the heater back on full blast. The temp gauge quickly returned to the normal range, and I proceeded the rest of the short distance to my workplace. When I got off work (10 hours later) I checked for leaks again and still found nothing. The coolant reservoir was pretty low but not dry. I added some coolant (maybe a quart) to bring it up to the fill mark on the reservoir, and went on my way. The engine warmed up much quicker than usual (especially considering it was about 25 degrees outside at that point), but didn't go past the normal operating temp on the gauge. (I suspect the rapid warm up time in this instance was due to the fact that I topped off the reservoir with straight coolant mixed with fairly warm water. Our building's pipes only supply hot water to prevent freezing. But I could be wrong.) I drove probably less than 5 miles to a service station to pick up some extra coolant just in case. When I got there I shut off the engine again and checked everything once more. Still no sign of leaks, and the coolant level in the reservoir hadn't gone down from where I'd just filled it. (In my thinking, this tells me that the coolant wasn't too low otherwise it would have drawn some of what I'd added into the system and would need still more now that the engine was warm.) After that, I started it back up and drove the 30 or so miles home. It acted completely normal on the drive there. It didn't get hotter than the normal operating temp and it actually cooled down to around 190 or so for a stretch of the drive. I drove it around town briefly on Friday and it never got warmed up to the normal operating temp. The engine was running continuously for 30-45 minutes while I was out about town. (In my thinking, this tells me that it's not having an issue with overheating otherwise it would immediately get warm and then proceed to overheat basically right after starting the engine.) I figured it had all been some sort of odd fluke, and that at worst I had just neglected to keep the coolant level topped off. Then today I went into the garage just to check for leaks one more time. Lo and behold I find a small puddle of coolant which had run out of the a/c condensation drain tube. It's definitely coolant and it's pretty obvious where it came from being that I added the old 5/8" tube extension to the condensation drain (as wisely recommended on this very forum).

But the whole sequence of events just seems weird to me. I think I know what symptoms to expect when experiencing an overheating issue, but these just don't add up to me. Can anyone make any sense of this and possibly recommend a course of action/investigation? Is it normal for coolant to come out of the condensation drain?
Sounds like your heater core may be beginning to leak. Borrow a cooling system pressure tester from Autozone or someplace like that.
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Definitely sounds like your heater core is leaking. Could be that you've got another issue too, but I'd plan on replacing the heater core at the least. As mentioned above I'd look into borrowing/renting a cooling system pressure tester, they're really the best way to find leaks as you can bring the system to it's operating pressure.
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You can make a by-pass hose and connect your 2 heater hoses together if you need to drive it. Obviously, you’ll have no heat.

I made some hose pinchers out of some scrap stuff I had laying around my shop so I wouldn’t lose to much coolant when I was putting it on.

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Update: Put in a new thermostat and haven't had anymore issues.

I was hoping it wasn't the heater core and decided to gamble on a cheaper and much quicker solution. I never got any coolant leaking on the inside floor board; just the one time leak underneath from out of the condensation drain. I don't know, may still be looking at replacing the heater core sooner rather than later. But it seems to be ok for now.
I don’t wanna jinx you sounds almost exactly like what happened to my heater core JUST before it started leaking into the cabin. I’m running a six auto 4.0 and I’m now the proud owner of a heater core bypass. If you have clean interior, have some rags ready.