Gather round friends, and hear my tale of woe.

I am slowly losing coolant. I don't drive it much, but I generally have to put about half a cup of coolant into it every couple months. I have:

No leaks on the ground
No coolant smell in the exhaust
No moisture in the passenger footwell
No visible leaks in the engine compartment

I have replaced the water pump, the thermostat, the radiator is new, the overflow cap is new. I am, quite frankly, going out of my mind. Does anyone know what could possibly be going on?

 

Check the left side valve cover make sure the throttle body heater is not leaking they can leak a tiny bit so it may not be noticable. Best way to find out get the disco up to temp and put some paper towel under there, check for moisture it may take more than one try.
Check every single hose clamp you may have a tiny heat expansion related leak from a hose end

 

head gasket......

 

I was under the impression this would manifest with steam out the exhaust and more significant coolant loss. I also had the oil sent out for analysis, which found no coolant in the oil. Is there another test I should do to confirm whether the head gasket has gone bad?

 

Have you pressure tested the cooling system to about 14.5 psi with a pressure tester? Leave it on about ten minutes and see if pressure drops or any coolant leaks are found? This is such a small amount that it could just be seeping from coolant tank or a hose fitting.... or a hidden heater core.

 

I haven't, but it's definitely on my list!

 

Since you've made it through the "not seeing anything obvious" stage, I would put that on top of your list... if that doesnt show anything, I'd consider pulling the spark plugs while you have it pressured up and sticking a scope camera in each cylinder.. bluetooth scope cams work great and can be had on ebay or amazon for less than $30. As a bonus, your kids will get your moneys worth sticking them up their noses, in their ears, and finding the remotes buried in the depths of your couches.

 

I had the same issue 3 years ago. Look at your dipstick. I'll bet you could have coolant leaking into your sump. Not good news.

 

Agreed on the HG, also agreed on the pressure test. Any codes? The HG leaks can start slow, eventually will cause a misfire. Be careful on the pressure test. I had one blow a hg, I pressure tested it overnight and it hydrolocked. I had to remove the spark plug to get it to turn over.

 

you need a pretty good HG gasket leak to show 'steam.' If you did an oil test, that seems like a pretty good negative indicator. Could be anywhere...just a pinhole....it fluoresces, so UV light and start looking all over?