Advice - JK CRD Dumping Coolant

[Jonye]

After about 40mins of driving the expansion tank dumps the coolant down to about 20% where it stabilizes. I have driven it up to 2.5 hours on the highway and it doesn't seem to move much from this level. I have been putting a bottle in next to the tank to catch the coolant as it's ejected and don't see any signs of coolant leaking.

I was getting a temp sender error code and the temp gauge would intermittently drop out. I replaced the temp sender and the gauge now gets to temp and sits half way.

Running the engine with the radiator cap off I looked in and saw some tiny tiny almost microscopic little bubbles when the engine reaches temp (pic included). My thoughts are also this could just be caused by the turbulence of the coolant cycling back into the tank.

I got a pressure test done at a radiator joint and they said it's holding pressure well although it was releasing a tiny bit of air near the cap (pic attached). So I changed the expansion tank and cap to an aftermarket one (pictured) but problem persisted.

I had a mechanic do a TK test and there are no exhaust gases getting in there. They fitted a new OEM radiator cap but didn't make a difference.

Would love to hear other solutions as while it seems to be driving fine, I hate to be driving around with so little coolant in the tank.

[Fishframe]

I can’t quite understand what you’re saying. Quote : “ I have been putting a bottle in next to the tank to catch the coolant as it's ejected and don't see any signs of coolant leaking.”

Are you saying -

1. It always dumps coolant out of the expansion tank down to 20%
Or
2. It dumps coolant out of the expansion tank, I then put more coolant into the radiator, and next time it dumps out to another 20% again?

Is it just that the radiator and expansion tank combined were overfilled?

[Jonye]

Coolant is exiting the system completely so the expansion tank has less than 2 inches remaining when the car is off and completely cool.

If you look at the pic you'll see I put a water bottle in there to catch the coolant to show it's not being released anywhere else.