Loosing/Smelling Coolant after Passing Pressure Test

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My wife has a 2018 Jeep Compass(2.4L) that she bought new, and since it was ~1 year old or so I've been occasionally smelling antifreeze when it's hot.

On a few trips to the dealership, I've mentioned this, and every time they claimed it passed a pressure test.

Back in the spring, it started throwing thermostat errors, and one of the things I initially did was top up the coolant, which at that point was really low in the expansion tank. I was pretty well convinced the thermostat was bad, but after looking at what was involved I basically said "Not doing it myself"(out of warranty at that point-she manages ~20K or better miles a year). She opted to have the dealer do it, and I once again mentioned the loss of coolant(it has to go somewhere, right?) and the smell. Once again, they claimed it passed a pressure test.

A few months later, I'm still periodically smelling antifreeze and it has once again dropped low. Since we have about 3K miles in a week coming up next month, I'd REALLY like to get to the bottom of this.

My mind is going two places. One is-does the expansion tank have a hairline that opens when hot, but might not otherwise show up in a cold test?

The second-I didn't watch them test it, but I'm guessing that they may have pressurized by removing the expansion tank cap. If that's the case, could it be the cap is faulty and simply missed?

I've added UV dyes before to catch oil and transmission fluid leaks. I'm wondering too if there's one I could use here(safely). I don't want to throw parts at it, but I'm almost inclined to just toss a new cap on it, or even completely replace the expansion tank. Any thoughts on where I could look?
 
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Testing or looking for leaks is pretty straight forward under the hood. If you have a slight leak under the dash where the lines attach to the heater core, or the core itself is dripping, your would smell it there. You could try pulling up the floor mats, and feel around for dampness . Like you said, it has to be going somewhere.,,,
 
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Add dye and observe

After that, I'd start looking at something that's only weeping when real hot and under pressure (coolant bottle/end tank crimps)

After that, I'd suspect pressure cap seal
 
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My 2016 low millage CR-V that I bough Feb. 2020 did not have the level of the overflow change any at all for many months. And this spring all of a sudden the level went from the middle of the two lines to only a few spoonful left in it. The radiator checked when stone cold, was full all the way. I though where did it go. It had to go somewhere. And I had noticed a slight smell sometimes recently. I looked for leaks, and though of borrowing or buying the pressure test equipment and testing it myself. And I sure hoped it was not the heater core, as I have seen some YouTube videos and post on a Honda CR-V forum of some having a heater core leak with CR-Vs that are only a few years old, though it is rare, but you have to rip the entire dash apart, usually also removing the seats to get good access.

Since it was not loosing much and not often, some said to just top it off once in a while. And of course I only would use the proper antifreeze which is the Honda premixed antifreeze.

I posted about this and someone said to replace the radiator cap. The sealership wanted $57.00 for a new Honda brand cap. And I have seen problems with off brand caps before so I wanted a Honda cap. But not at that price. I bought one with some Honda antifreeze from OEMPartSource.com and they sell original Honda parts and fluid, and also original parts and fluids for some other brands. And there price for an original Honda cap was less than $20.00

I toped it off and put a new Honda radiator cap on it, and it has remained stable for several months now, and the overflow bottle is at the same level when it is stone cold.

So when you can not find the leak, putting a new original equipment Dealer brand cap on it is not a bad idea. It did work for me.
 

bunnspecial

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Thanks-I'll go the dye route and see what that turns up.

For mentioning replacing the cap-I had always been under the impression-maybe incorrectly-that on this sort of system the pressure cap is on the expansion bottle and the "radiator cap"(as in the eared metal cap on the radiator itself) is a solid sealed cap.

If the dye turns up nothing and I end up replacing the cap, which cap do I change?
 
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Jul 14, 2014
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Wisconsin
Some Durangos had a subpar radiator that had hairline crack open when hot. I could always smell antifreeze in ours, but it didnt start to get low until around 75K miles.
I finally found a drip at 110K miles.

Just FYI


It might not have been a crack, but bad crimping of tanks.
 
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Jun 28, 2003
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6,492
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Illinois
Over time the OE spring clamps start to loose tension and will leak at the engine end on my Hyundais especially if they have ever been removed. Usually this is manifested by coolant stains on the pipe or wetness when cold underneath the clamp/hose. And usually the expansion tank moves little but the radiator will be low when cold. But it won't leak when under pressure.

Ford radiators were like this too in the 80s-90s with the crimps on the side tanks, leak brand new.

I swapped out the clamps for good worm clamps, which need to be periodically checked for tightness so mount in accessible orientations.

And I use this in stubborn places.

Permatex 85420 Permashield Fuel Resistant Gasket Dressing & Sealant​


619poH8OcdS.__AC_SX300_SY300_QL70_FMwebp_.jpg
 
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Joined
Jun 26, 2014
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846
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Northern Arizona
Take a close look at the water pump.

I had a 05 Prius that I bought used (70k miles) and occasionally smelled coolant when it was hot. I worked with the guy I bought it from and he said he took it to the dealer more than once for the smell, but they always told him there was no leak and just topped off the overflow tank. He kept all paperwork and I recall it started before 40k miles. It never dripped under the car, and only needed 10-12 ounces of coolant added once a year, so I didn't worry about it. A year or so later I was reading about how common water pump seeping was with the gen 2 Prius so I took a look. Sure enough, there was a buildup of pink crust just below the weep hole. I changed the pump and never smelled coolant again.
 
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