2014 Jaguar F-Type S V8 - 40k miles

Timeline
June 30th - Driving home from from work got a "low coolant" light on the dash, went away after 2 minutes, didn't think anything of it. Temp stayed right in the center

July 1st - Driving to work in the AM, got a "low coolant" light on the dash again, went away, came back, etc etc. When I got home checked the engine bay and found coolant splattered in a 6" radius around the expansion tank cap. Found there was a TSB for it, figured it wasn't seated well. Let things cool, topped off coolant, and re-seated the cap.... cleaned the engine bay to look for new coolant splatter. No other coolant to be found anywhere in the engine bay or on the ground.

July 2nd - Drive the car 3 hours 3 minutes to our lake house, no issues what so ever. When I arrived I sat in the drive-way for like 30 seconds and the car's temp maxed out... By the time I noticed and started to kick the heater on to see if that was the issue (it was like 90* out) the temp went back to normal. After I shut it off 30 seconds later, the radiator fans sounded like they ran normally.

July 3rd - Was out doing errands and eventually low coolant came back on, went away, etc ... no issues until again I pull into the driveway and sit for a second .... temp maxes out and this time when I shut it down the radiator fans were running full bore. Topped off coolant again.

July 5th - Drove around for a while with the AC on and had an OBD plugged in to see actual coolant temp vs. the vague gauge on the car.... coolant ranged from 194* - 200* the whole time. Never went above.

July 6th - No issues driving a few miles here and there around town. Car got up to temp 3-4 different times that day. Noticed more coolant around the cap

.... I drove my other car back to Chicago and plan on having the F-Type towed back to me tomorrow.

Whats wrong?!
Current thoughts / theories -

1. ) Expansion tank cap spring is bad ... letting coolant out after it gets warm, then the cooling system tries to exchange the same heat load with less coolant. Explain the coolant around the tank
Why this: No issues at speed with plenty of fresh air coming in, heat load without fresh air pushing through is too much Maybe when I added coolant I trapped air in the system and didn't bleed, air pocket made it worse.

2. ) Thermostat sticking -
Why this: I did see consistent issues. Perhaps at idle it just sticks closed then jumps open.

3.) Water pump on the fritz
Why this: Enough air cooling when at speed, when stopped the lack of airflow causes it to over heat. Hot hot hot coolant overpressurizes and pops cap as its designed

4.) Head gasket
Why this: I think its unlikely because I don't see white smoke, I don't see consistent issues.... but a lack of a dipstick means I can't see if I have milkshake oil. Maybe the exhaust pressure is forcing out the coolant via the cap.

Anything else I can do to further trouble shoot before taking it to a dealer?!
Thanks for any help!

 

I also think in the same order you have , 1, 2, 3.. I would however rule 4 out asap, if you have a mini vac, pump it out and see, if all good put it back..
if you don't have one, you need to get one.

 

The expansion tank cap should be tightened until it clicks three times.

Maybe try a new cap.

Then top up coolant and keep a visual check on the coolant level by removing the cap each day before you start the car.

This will give you a good idea if the level us dropping and if so by how much (top up to max each time and note how much is added .

If the level drops a lot and the cap is OK then further checks need to find the leak.

Think it's unlikely to be head gasket but I believe you can get test strips that when dipped into coolant will indicate if exhaust gases are in coolant (sign of head gasket leak)

 

Some people on here have reported issues with the coolant cap so you're not alone if that's the problem. Not sure if their solution required a new expansion tank as well.

 

Most likely the expansion tank / cap is leaking at pressure. But these engines are so sensitive to overheating (Aluminium block can warp) that you are right to have it towed and let the dealer work it out. Don't take the risk!