i have a s type jaguar 2004.over the past few weeks i have had the low coolant level red light on the dash lighting up,so i pull over release the pressure and top up,but even when the water tank has been topped up the red light still comes on again after a while,in the end i got fed up with stopping and topping up,and carried on the water temp stayed as normal but the low coolant level was still on,then so one told me that it could by a doggy sensor on the water tank,and the reason that i was having to keep topping up the tank was because when iam taking of the water cap iam letyting out the water as it is under presure,so all iam looking for is where the sensor is and can i replace it without haveing to replace the whole expanstion tank,many thanks for any help on the matter.