hi
Ideally you need to plug in and see what faults you get, they should point you to the right direction
if coolants ok, could be a bad coolant level sensor or waterpump, plugging in should tell you and you could also monitor the cooland temp, as the gauges on most jaguars dont show correct temp, they just a visual indicator, the either show normal or full, high temp, there usually no in between, but with a diagnostic tool you can actually monitor the actual temperature
cheers
Joe