I tossed the factory plastic / nylon coolant line years ago and replaced it with a solid rubber coolant hose. It lasted five years or so before the engine bay heat cooked it too hard for my liking, so I replaced it again....

 

I had lots of trouble with the sensor. I bought a new tank with sensor. After a while i get the messages back. Apparently it was a reproduction tank that failed. You need the expensive original with the original sensor. When replacing it, refill the coolant with a vacuum filler. That device can be bought for around 25,-- GBP or 35 EUR. Burping the system is not enough to refill the coolant. I had this advise from my Jaguar specialist and this solved the low coolant problem. Soon after the succesfull replacement of the tank, i had the head gasket of bank 1 blown. Apparently it was part of the trouble in the first place.

 

Low Coolant message fixed.
I was getting the Low Coolant warning randomly on my 1996 XK8. Levels were all good. Could have been sticky float since 21 years old at that point. Garage advised new expansion tank (bought and fitted part number MJD4400AB in 2017). Problem not really fixed, kept coming on occasionally. Levels all good. Degas tank in wheel arch about 1cm full.

Then I found a Jaguar Technical Service bulletin 303/15 from Oct 1997. It says that a later model expansion tank is compatible with a 97MY XK8, but you have to swap the hoses over. Of the two pipes coming out of the tank, the rear one is plugged up on the replacement. The hose that used to go from here to the thermostat was now swapped to the radiator. The hose from the thermostat also now goes to the front of the two connectors on the expansion tank (not plugged up). I used the end of a Sharpie pen to quickly bung the hose up, so no leakage, while my finger blocked off the expansion tank tube.

I ran the engine up to temperature. Temp gauge in car sat at 50% as it always does. No message. Took the car for a long drive, going over bumps, stopping and starting. No low coolant message, temp gauge still 50%. Did this a week ago, driving every day, no message still. No smell or evidence that engine is getting hot (summer here in UK Malvern). When I turn engine off, radiator cooling fans were not on (but I know they work). Degas tank always sits at 1cm full and never changes.

Not quite sure how I have fixed the problem, unless I have done something stupid and engine is about to blow up.

I may also use the syringe method to 50% fill the degas tank, just to be safe.

(BTW - double success in the last two weeks, since I resoldered the joints in the ABS module and made the Stability/Traction control warning go away - hasn't appeared since.

Dan