Coolant leak, no puddles

[mt_]

A few days ago, I noticed a boiling noise coming from under the hood after a short drive in my 2006 Rubicon, so I opened it up and saw the coolant in the overflow tank boiling. The level of coolant was getting low, near the ADD mark. I don't have any coolant (ordered, hasn't arrived), so I drove it the next day without adding any more coolant to the overflow.

After I parked, I checked the level in the overflow and it was empty, and once it cooled I checked the level in the radiator, and it was almost full. After leaving it overnight, I checked it again and the coolant level had dropped in the radiator, and I topped it off with ~1-2 quarts of distilled water. There were no puddles on the ground below the Jeep. I did a pressure test and didn't find any leaks, and also checked the oil, it didn't seem to be milky, and the level was the same as the last few weeks. I took it to a local shop, and they didn't see any leaks either, and said the oil could have some coolant but they weren't sure.

Any ideas on what this could be?

 

[JKP]

If the temp gauge is indicating normal temp, replace the radiator cap. A bad cap will not hold pressure which results in the boiling and overflow.

You can sample the oil and send it off for analysis to determine if there is antifreeze in it.

 

[mt_]

If the temp gauge is indicating normal temp, replace the radiator cap. A bad cap will not hold pressure which results in the boiling and overflow.

You can sample the oil and send it off for analysis to determine if there is antifreeze in it.

It is indicating normal temp. If it is the cap, how come the level had dropped overnight? I opened it after it had cooled for a while the night before, so I don't think it could've condensed much. I will try replacing it though, I'm hoping it is just that.

I am going to do an analysis with Blackstone, but wanted to see if there is anything else I can check in the meantime, since it can take a week or two.

Thanks for the reply.

 

[tr21triton]

how many miles on your Rubi ?

 

[mt_]

how many miles on your Rubi ?

Just hit 80K.

 

[cpwolf]

My experience is that it when you’re boiling like that, there is a small leak and pressure not holding. Cap is the easiest, crack somewhere else can leak out, and the liquid turns to steam.

I’d look around for marks of coolant cooking on a small area.

I had that on my son’s 2008 JK and sure enough, someone put too much tape and tightened temp sensor and there was a crack in the manifold.

I’d start with Cap.

 

[tr21triton]

like JKP said replace the cap. pressure increases the boiling point of the coolant. so if the cap isn't holding pressure it will boil and overflow your reservoir.

 

[Unique Username]

Monitor the heater core. You could clamp of the lines when you shut it off in the evening. If the level stays the same, it might be a slow leak from the heater core. Mine was a very slow leak. It would leak at the core and mix with the water from the AC evaporator and come out looking like water. Turned out it had a slight mixture of coolant and I was loosing coolant.
Depending on your location, if some place super dry, the core could leak and evaporator before leaving spots on the floor.

 

[JKP]

It is indicating normal temp. If it is the cap, how come the level had dropped overnight? I opened it after it had cooled for a while the night before, so I don't think it could've condensed much. I will try replacing it though, I'm hoping it is just that.

I am going to do an analysis with Blackstone, but wanted to see if there is anything else I can check in the meantime, since it can take a week or two.

Thanks for the reply.

It's possible there was air in the engine block.

But, replace the cap, top off the radiator and overflow, and look for cracks/leaks in the radiator, check the AC condensate line for antifreeze, etc.

80K, holy crap, I'm at 280K.

 

[mt_]

I just replaced the cap, filled it up and checked for leaks again. I will see what the level is like tomorrow.

I'll try clamping off the the heater core lines next if this doesn't work. It definitely not dry here, I'm in the North East, nothin but humid.

 

[Cornbread]

I've had nothing but trouble with the heater core in mine. Took me quite awhile to even figure out it was leaking.

 

[mt_]

After 10 days it still seems like the radiator cap fixed it.. can't believe I overlooked it. Thank you everyone for the help!

Now to work on fixing the rest of the pesky leaks... rear main seal is gonna be a little bit harder than the radiator cap.