slow coolant loss

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2014 Sentra. 92k miles. it loses about 1" of coolant per month. no visible leaks (I used UV dye), pressure tested system (cold, obviously) and just had a UOA done with no evidence of coolant in the oil.
since it has a warranty, I have an appt at the dealer. they are claiming that they just want to do a coolant flush/fill (for a million dollars) and that they will test the system as part of that.
I expect they will claim all is good and I don't have a problem.

I also expect it's a head gasket issue that only exists when the engine is warm, but cant prove it. there is no bubbling in the radiator when running.


thoughts?

(we've had the car since new; it's never been overheated; actually it's had zero issues except repeat issues with the CVT)
 
Curious what responses you get to your question.

I have to add about half a quart of coolant to my 530i once a month or so, and I don't know where it's going either. I don't see coolant puddles on the ground, and when I did a UOA recently, it did not show any antifreeze presence.
 
It could be getting into the cylinders without getting into the oil passages. Head gasket, or a cracked block or head.
 
If you've pressure tested the system and UV dyed it too, there's only one other test I can think of and you alluded to it even though no bubbles seen. That is a radiator combustion gas test for the block/head gasket. If it passes that, seems something you're going to have to live with until/unless something more obvious shows.
 
I had a radiator cap go bad on me and it caused a big loss. Might not be your cap but they're cheap enough to throw in a new one and see if that helps.
 
Your post of 1" loss per month is not very exacting. If the 1" loss was measured in something that had an area of 1" or 2" inches it would not be much. 1" loss across the area of a radiator would be concerning. 1" loss across something with the area of Great Lakes would be huge. So 1" loss does not mean a whole lot.

The water pump could be weeping and on its way out. You could have a small leak in radiator core that was evaporating as fast as it leaked. Hoses?

A pressure tester or leak detector might help.

This will cost a few hundred. Hopefully not the heater core which can be expensive to take apart to get to.
 
I had the same thing happen on my Jeep. After about a month I crawled under it after driving 20 miles to work and found the lower radiator hose seeping. A little turn of a wrench and it was fixed.
 
I had a similar situation in the old truck. When it was cold it would leak out of the coolant line to the heater core. Once warm it would stop I would add maybe 3 cups every month when towing. I found it by accident one day. Replace the hose and clamps never had a problem again.
 
Try replacing the radiator cap. I had a car that was doing the same thing and it was cooking off through the seal on the cap.
 
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my 84 4 cyl olds ciera has a block porosity that was a super slow leak. one or two drops per week.
fix was new block. not new head. dealer changed gaskets, head,
hard to find the leak
 
I have had head gasket issues in cold weather, at night when the head gasket contracts, (you being in Chicago really cold at night) tiny cracks appear and coolant is sucked into cylinders, burns off when car is started with some white smoke Thus no appearance of a leak. Happened every winter for me but a half can of head gasket sealer in coolant does the trick. My son currently has this issue, fine in the summer, but loses coolant in the winter. Last Dec we put a half can of sealer in and he was fine all winter.
 
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