You could try a cooling system/radiator pressure test. It builds pressure over the radiator cap and you see if pressure drops after some interval of time (unsure of that time length). If it falls, you have a leak somewhere, be it outside or inside of the engine.

 

You have to check for combustion byproducts in the coolant, they make cheap testers that alert at the presence of CO2 in the coolant. I had a head gasket leak that had no symptoms for quite a while before showing itself. Well no symptoms other than coolant disappearing without a trace.

 

How about a radiator sealer?

A radiator sealant that will work with your coolant.

 

The radiator cap should be rated to keep 18 psi pressure; if I were you, I would try using a Mopar cap and see if situation changes.

If it does not change, try what @cDee63 suggested: test the coolant for CO2 presence in it

 

I think it should be 17psi Mak.

https://www.worldpartsdirect.com/oe...HRzJmE9amVlcCZvPWdyYW5kLWNoZXJva2VlJnk9MjAwMyZ0PW92ZXJsYW5kJmU9NC03bC12OC1nYXM=

 

 

Absolutely Snowy.

 

I had coolant issues for almost 2 years. The coolant level would be fine and then drop. No leaks until I touched the band clamp and then I would get a small leak every 2 weeks. Finally thermostat, and upper hose was replaced and I thought that cured it. No- started losing coolant again, mechanic found out my electric fan(4.0) was very hard to turn so that was replaced. I told him I had replaced the radiator cap with a Duralast one and he said the gasket was not sealing and he thinks that coolant was leaking out from the cap and burning off on the radiator. The radiator was also replaced as the side seam burst when it overheated. Have not had an issue with it since.

 

When the mechanic refilled the radiator and block with coolant after the repair did he remove the bleed plug located where the upper radiator hose connects to the engine. If he didn't you will have air in your cooling system. I suggest you remove the plug, when the engine is cool, remove the radiator cap and have the proper coolant on hand. Start the engine and as it warms up and the T-stat opens add coolant as needed until it overflows from the bleed port. Button it all up and take it for a drive. See how your coolant level holds after a few days of use.

 

I had an issue similar to this where I would be low in coolant. No visible leaks. I replaced the band clamps on my rad hoses with spring clamps like OEM. No more coolant loss.

 

You say there's no visible leak - if you're not getting any liquid on the driveway, be sure to look for evidence of dried coolant.


I hope it's not the case, but the problem could very well be a blown head gasket which would let coolant into the engine where it goes out the exhaust as steam.


Is the engine making white smoke? Check the oil - is it milky? If so, that's the problem.

 

What WJPAUL said.

If there is no sweet smell while you drive and no wet areas around hoses or waterpump. I would guess, since the upper hoses aren't getting hot, that the system wasn't bleed properly.

 

Time for coolant leak tracing dye

Add coolant dye to the radiator and wait a week. The leak location will be marked with a bright green stain under UV or violet light. You may need to borrow or rent a UV inspection light. See:

https://tracerproducts.com/leakfinder-products/coolant-dye/

LF3001CS is the single dose size available on Amazon for $7.

Fluorescent dyes are often available in different colors to differentiate the medium being traced. Yellow for refrigerant, blue for motor oil or transmission fluid, etc.

A friend had a beloved BMW 733i he bought new that picked up the habit of constantly losing coolant. The BMW dealer sold him a new radiator, hoses, service after service, ultimately amounting to big $$$, but the coolant loss continued. He finally trusted me to try to find the leak with dye. I added yellow Tracerline dye. After a week of driving, he brought the car over after dark for an inspection. There were two leaks - the top of the white plastic radiator expansion tank had subtle fatigue cracks with a big fried egg yellow dye stain on top; leak number two was a white plastic heater valve with tiny cracks and a small yellow dye stain. I changed the expansion tank, but was not equipped to remove the dash to change the heater valve, but the bottom line is the leaking stopped.

These leaks can be hard to isolate because often water vapor is leaking, not liquid water. If the leak is in the heater core, you may see green dye stains in the condensate dripping from the air conditioning evaporator drain.

Be sure to use distilled water as make-up water and not tap water to avoid plugging up your radiator with mineral deposits from hard water.

 

When I was trying to figure out where my coolant went. It ended up in passenger side floor carpet. Whole thing was soaked due to broken heater core.

 

Heater core leak



The wife's 1996 ZJ suffered the same fate as @BlueOffroader. We took the dash out and replaced the heater core early this spring, 2021.

Our coolant leak symptoms were strange. We had 'waterfall noise' frequently from the heater for years and wet carpet (but no antifreeze) to confuse things (rain leak). The engine, trans, and transfer case were all rebuilt last fall with the body sitting undriven for about 2 months in fairly warm weather. When the cooling system was refilled, the heater core leaked like mad at first, the carpets obviously stained with sweet-tasting antifreeze. A new heater core was quickly purchased, but for no explicable reason, the leaking quickly stopped and the radiator held pressure. We again had 'waterfall noise', and the rain leak into the cabin, but no antifreeze soaked carpet. Somehow the heater core had healed itself.

This past spring of 2021 we bit the bullet, pulled the dash and installed the new heater core purchased the previous fall; rain leaks were caulked. No more 'waterfall noise' nor wet carpet. On inspection of the old heater core, there were multiple blue-green stains where it had been leaking, but after back-flushing the core in the kitchen sink, a ton of blue-green sludge came out.

My theory is the sludge was plugging the holes; the sludge dried out and shrank while the vehicle was under repair, so the core leaked like mad initially, then the sludge re-hydrated and expanded to plug the leaks. After driving, when the engine cooled off, air entered the heater core, causing the 'waterfall noise'. Many Jeep GC owners have reported 'water sound', 'waterfall noise', 'sloshing noise', etc. I suspect these are all heater core leak sufferers with air in the heater core.

 

The mechanic said that he found no other leaks after preforming a pressure test on the cooling system and also no signs of a bad headgasket.

Welp it's going somewhere, and the number of places it can go is limited. If it's not on the ground it's out the exhaust.

Just because he can't find it doesn't mean it's not disappearing.

 

it could be paranormal activity in his cooling system. :surprise:

 

Probably just steaming out of a defective radiator cap.

 

Ditto

 

Have you had any luck finding the problem yet?

 

I was losing about 1 quart coolant per month for three years and it was coming from the thermostat housing. I installed probably 3 or four of the paper gaskets to try and fix it and even replaced the thermostat housing, but made no difference. There was rarely any real sign of moisture anywhere and nothing getting to the ground, but I would see a small buildup of some yellow pasty stuff below the housing on top of the water pump. I never used anything but the paper gaskets because I did not want to have to scrape off the silicone if I had to go in again, but about 3 months ago, I replaced the paper gasket one more time and generously coated both sides of the gasket with the permatex RTV cooling specifically for water cooling systems. Have not added coolant since. Do not know if that info can help you, but good look!

 

Perhaps everybody already knows this,

Paper gaskets need soaking in water before they are used.​

Took me years to find out.

 

MY 01 WJ was fine then started losing coolant. The hose that attaches to the side near the radiator cap was the issue. I could see where it was wet after driving maybe 6 miles. I put a clamp on it and no more losing coolant. Also my Duralast radiator cap was replaced earlier this year as it didn't seal as it should.

 

Delta0,
Thanks for that info! I did not know that you are supposed to pre-wet a paper gasket - which is probably why they did not work for me on my Jeep 4.0. I know the principal that the paper swells to seal when it gets wet, but did not know you do not install them dry. When you say it "need(s) soaking", does that mean a quick dip in water, or letting it soak for a certain amount of time? Very interested in understanding! Thanks again!

 

I take it to mean soaking until it's all wet and floppy WK.

Soaking until it's mouldable enough for the high spots
on the mating surfaces to squeeze it from high spots
into low spots.

As, when, and if the take the joint apart, you should be
able to see moulds / prints of the mating surfaces.