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Very Strange Coolant Leak?


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Hey guys! So I have been dealing with a very strange coolant leak these last couple of weeks. It seems to be accumulating by my lower control arm mount on the passenger side (see attached photo, sorry if it's dark). It is not very consistent at all. Some days I can drive all over, and nothing leaks, and then I will start and run the truck for a bit and it will leak. Just yesterday I literally watched the cooling system pressurize and waited until the t-stat opened and I didn't see it leak a drop of coolant... Today I was adjusting my headlights and let it idle for like 5 minutes. Nowhere near long enough to reach operating temp... and voila coolant dripping from that spot :brickwall: 

 

Due to the location of the leak, I assumed it was a pressure bottle problem. I have inspected the bottle, and the hoses connected to it, and nothing there is leaking. Even so I am buying a new pressure cap (from napa) tomorrow morning just to make sure it seals perfectly. I am pretty much at a loss here at this point. I can't think of any other sources that it might leak from, even if it was a freeze plug, it would leak from the back of the block and likely wouldn't accumulate in that location. If it was on the side I would see it and notice it leaking. Another factor that leads me away from that diagnoses is that there is spattered coolant underneath the bottle sometimes... it's really starting to drive me crazy. Do you guys have any idea of where it could be coming from? I am almost certain I didn't over pressurize the system, I NEVER fill it over the half way mark if I add coolant (if I even fill it to the half way). Maybe there is a hairline crack on the bottle, but that makes NO sense since I watched it pressurize and it didn't leak or spray or hiss even... Any help would be amazing! Please feel free to ask me more questions or for more pictures.

Coolant leak.jpeg

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That's a very odd spot.  There isn't any sign of coolant elsewhere?  

 

My first thought would be rear freeze plug if you see coolant this far back but it likely wouldn't reach the frame rail.  The only other thing I could think to do is check you passenger floor board and hvac box drain to see if it you heater core is leaking maybe.  

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Yes it is a very weird spot, I have looked on forums for like 2 hours and haven't seen anything about this spot. I haven't seen any coolant anywhere else, except on the tire, and the front lip (assuming that's from the tire throwing it there because it was splashing quite a bit for a while). I would assume the heater core as well, but I just replaced it not 6 months ago because it was puking on the floor. What does the HVAC drain look like? Is that the large black cylinder that connects to the intake underneath the pressure bottle lol? I am still pretty new to Jeeps so excuse my lack of knowledge!

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If you look at the firewall behind your oil filter you will see a little black spout an inch or two long.  If this gets plugged it can cause water, and coolant if your heater core is leaking, to leak out of the box on to the floor and such. 

 

If you already replaced the heater core it's unlikely this is the issue but worth checking around to make sure.  

 

Do you still have the black plastic heater control valve thing in the hoses going to the heater core or are they solid hoses from the front of the engine all the way to the firewall?  It would be almost directly above the oil filter.

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Okay, I will check that out tomorrow morning and see if I can see anything clogging it or dripping from it.

 

I did just search again and I found a thread about someone whose heater core was going bad, and they said it dripped from the exact spot that I am talking about. I am going to scream if I have to do that heater core job again. I have no idea how it could have gone bad this fast... They said to check to hoses that connect to the heater core and re-seat them. I'll give that a shot too.

 

As far as the plastic valve thing goes, I think I do! There is definitely not just a hose running from the front of the block to the heater core.

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Yeah hopefully it's not your heater core.  Really sucky job, especially doing it twice.  

 

Those heater control valves are known to fail and they leak coolant all over in that area.  I almost forgot about that since I don't have it on any of my Jeeps anymore.  If that is the problem, just take it out and either get new hoses that run all the way to the firewall (97+ XJs have the correct hoses so search for them rather than your year MJ).  Other option is to get unions and hose clamps and splice the hoses together.  The valve is useless really, and you'll have no issues without it.  Just be sure to plug the vacuum line if you remove it.

 

Post up your findings, really interested in what this leak will be from.

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Indeed, I am really hoping it isn't! 

 

I will inspect that too! I sorta felt around by it and it didn't seem to be leaking but I may have missed it. I will definitely look into deleting the HCV if it does end up being the cause of the leak! 

 

I will definitely post my findings as I work through it. I am hoping I can find it tomorrow because we are expecting a deep freeze here in Colorado so I am not gonna be able to work on it for a few days :(

 

Thanks for your advice and tips!

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Update!

 

So I just went in and checked the hoses connecting to the heater core, they seem good and tight no sign of leakage at all there -I tightened and reseated them a little bit anyways. I felt around the heater control valve and it was bone dry. I am going to check the valve when I get home after it's been running for a bit and see if I can see any leakage from there. 

 

Also, I believe my HVAC drain has broken off... I don't see any drains extending out from the HVAC system, so that would likely mean it would be leaking in the interior if it was the heater core, right? I am starting to suspect the heater core... but I don't see how it's possible for it to go bad when I changed it only 4 months ago. Also the heat still works in it after the engine warms up so I know it's still flowing.

 

I'll keep updating you guys!

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Okay I am pretty sure I just found the leak...

 

Was sitting outside, letting it idle because my fan shroud screw decided to disappear today making my shroud hit my fan like crazy. Zip tied that, looked at the heater control valve, and in the 3 degree weather noticed steam coming from a a connection near the HCV, gonna tighten it later... but then, suddenly, coolant just EXPLODED out of my pressure bottle from around the cap. I am not sure how this could have happened only this time...? but it definitely did. I feel like this is certainly the source of the leak. because of the sheer amount and force that came with it and if the cap isn't sealing it, all of the hot water in the coolant just evaporated straight out of the bottle while it was cooling explaining why it was all gone... Crazy

 

I am going to put on the new cap, and post the results here later this week to let you guys know the stats!

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I'd grab yourself a new radiator cap.  They are designed to release pressure at like 15psi or something like that.  If yours isn't working properly then you would be building pressure in the cooling system and the weakest link would be your expansion bottle.  

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i'll have a open radiator out of mine soon(like in the next week) if you are interested. it works fine, just swapping so that i can have a coolant sensor. otherwise there less then a 100 $ to convert to open iirc.

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3 hours ago, fiatslug87 said:

I recommend getting a Mac's aluminum bottle or changing to an open system if your radiator is not relatively new.

Where do you buy the aluminum bottles?

 

My rad is very new actually, so I’m prolly gonna stick to closed until I eventually swap the engine out! I went ahead and bought the default Napa Cap, so I’m gonna see if it holds the pressure better, if not I’ll grab that Volvo cap. Thanks for the part number :) I went to Napa to buy one based off an old part number from an older thread, but they gave me a green one that was a tiny bit too small. 
 

Honestly I have no qualms with the closed system as long as the parts are in good health, which most seem to be good. Although I definitely plan on doing it within two years!

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