I would definitely pursue this while your car is under warranty and take it to an authorized LR dealer, just to document your issue. Sounds like you may have some air in the system based on the overflow above max. Have your mechanic bleed the system and refill. Just a suggestion.

 

Been through this 4 times with JLR vehicles (not my Defender though). One time ended in a blown engine at 35k miles due to a head gasket leak. The other 3 times were just coolant line leaks.

My suggestion would be to use an undiluted degreaser like Simple Green. Take off the plastic engine cover. Spray and clean the engine and engine compartment while engine is cold. Get it spotless. Rinse it and let it completely dry. Run the engine in place in your driveway until it's hot and then keep running for a few minutes while you look for anything that's wet. These leaks can be so small that they're just a mist. You might not see the vapor but you might see a greasy wet spot. You might have to drive it a bit before something shows up.

If that doesn't help, get some UV coolant dye and a blacklight. Use an inspection camera to see lower parts of the engine.

If you still can't find it, have it checked for exhaust gas in the coolant (head gasket problem). You can do that with an at-home kit or take it and have it done. Good luck.

 

Just dropped my 2020 P400 off today for low coolant. No warning lights, but the reservoir was empty last weekend. I filled it. Then all week whenever I parked and got out I could smell the coolant very strongly. No spots easily visible, so I hope. Y dealer takes their time to find the leak. Fingers crossed!

 

And here is the response from my SA about the empty coolant reservoir being topped off and then me smelling coolant strongly after good 1+ hr drives…


“It is possible that you are smelling the coolant that gets pressure released through the reservoir cap as it does this to not get too high of a pressure and boil the coolant. It is still worth verifying so I will let the technician know to do the overnight test drive for you!”


Guess I’ll find out what the verdict is from an overnight drive since the pressure test and visual inspection showed no leaks…

 

I'm sorry but that's f-ing ridiculous. They just make this crap up.

 

That is some of the best fiction I've read in awhile... I never understand why these knuckleheads feel the need to throw BS around instead of just looking into the issue.

 

I tried looking all last night if a “coolant reservoir cap can release pressure”….to at lease humor the response I got…

all I know is I smelled faint coolant one day, checked the reservoir and it was empty, filled it, and the smell was very strong there after.

 

The cap is designed to release pressure if necessary but that's not where your entire reservoir of coolant is going.

 

Right now I’ve figured the entire reservoir emptied sometime between May & January…I know I checked fluids in between them and noticed the tank still having fluid, but by January it was just empty…

so the leak down seems to be either pretty small…or I question if these vehicles just burn off coolant naturally…

 

I’ve had this “mystery” coolant loss since new - no smell, no visible leaks, no help from the dealer.
I was adding coolant every 1,000 miles, then 1,500, then 2,000 miles. Now at around 12,000 miles the coolant level seems stable and hasn’t dropped for the last 3,000 miles. So air pockets in the system? Small leak that sealed itself? Other?
Weird.