Coolant overflowing from header tank

[Two JAGS is not enough]

I am in the south of France, it is hot!
Today, my 2014 XK has decided to let a large amount of coolant out through the filler cap. There are no messages, no lights, car runs fine. This happens about 5 mins after I turn the engine off. Should I let the car idle for longer? I have topped up the coolant, taken it for a drive, then it does the same thing again. Any suggestions as to the cause would be appreciated. It drove here all the way from the UK with no problems, maybe it is just too hot here?

[Astromorg]

Are you sure you're not overfilling the system? Unlike earlier XK8/Rs, the XKs have no atmospheric overflow tank to take care of situations such as yours. ''Expansion and contraction of the coolant is accommodated by an air space in the expansion tank and the compliance of the flexible hoses'' - Jaguar's words! To achieve this, the maximum fill level, marked on the side of the tank, leaves a 1 to 0.5 litre air space in the tank when cold.

If the engine gets too hot, then the fans should run on after shutdown to cool it. If no fan run-on then it may not be overheating. Or maybe they should be cutting in and are not!

No teaching of sucking eggs or the like intended here!

[RMA37]

I'm not sure I agree that the engine is overheating if the fans come on. I've only had this happen on my XK8 once, and that was last week when I took it out for a fast run in 30 plus ambient temp. I put it in the garage and the fans ran for a few minutes. No sign of overheating at all, and my BMW will do the same at times particularly when abroad. Aluminium heads can distort if overheated and when the engine has stopped, the hottest part is the head, hence the requirement for the fans to go live.

Mine has an air gap in the filler tank and I also use Evans coolant.

[Astromorg]

Sorry, I don't mean overheating other than the temperature higher than normal such that it requires the fans to be running after the engine is shut down. Perhaps for some reason Simon's fans are running only when the engine is running and not, if required, when he shuts down, hence the overexpansion of the coolant and spillage. The airgap when cold is essential.

[IndigoBlueMk2]

2014 XK Signature, 9500 miles.

Further to my earlier post about the coolant overflowing in September 2019, I changed the cap on the reservoir, and all has gone well, even though the car has not had much use in 2020. I just went on a journey from South Wales to Reading, and on the way back, stopped at a services to make some calls. While sitting in the car, I noticed steam coming out from the bonnet just in front of me, and the car had pushed coolant out through the cap again, about 1.5 litres, judging by what I had to put back in.
I have noticed that the cap, when screwed on, seems to 'slip' on the plastic thread before tightening sufficiently to get the clicking sound when it is tightened correctly. The coolant is the right type, put in by the Jaguar main dealer, and the level was correct, definitely not overfilled. After my problems last year the coolant was changed at Jaguar Swansea, and the system tested, with no problems found. Car has also had a full service this year and a clean bill of health. I have decided to buy a new tank and cap, just to see if this solves the problem. Has anybody else had this issue? My other concern is that my fans NEVER run on after the car is switched off, are they supposed to?
On this model there is no temperature gauge, so I have no idea whether the car is actually running too hot. If I got an OBD reader and left it plugged in while driving, would that tell me the temperature?

Any help is greatly appreciated.

[mike020150]

In very hot conditions, the cooling fans are designed to run on after engine shut down for up to 4 minutes. The cooling fans are controlled by a cooling fan module built into the fan unit plus signals from the engine ECU. First, it would be as well to check the plug connector linking the fan unit to the wiring system. Then, if all's OK there, to eliminate all suspicions about the fan unit, it would be as well to have the operation of the fan control module checked by a dealer or specialist with Jaguar diagnostics (or the appropriate Autologics modules). Mike.