2001 XK8, 59K miles. Low coolant light came on the other day. Reservoir was down a little. That made sense because I had been doing a lot of highway driving on hot days. I topped it off. After about 100 more miles and two days later, it's on again, but tank is full. Gaskets were replaced recently. Thermostat is about a year old. Engine temp is normal. I don't believe this is a leak.

Could it be a switch? Bad cap on the tank? Other possible causes or symptoms to look for, anybody.

 

Its more than likely the sensor in the expansion tank. Some people have removed the tank and tried to repair the sensor. There are a thread or two with some pictures related to that.

Or, you could just buy a new tank online for $170 roundabouts, and fix it that way. comes with the sensor installed and a new cap.

 

"Or, you could just buy a new tank online for $170 roundabouts, and fix it that way. comes with the sensor installed and a new cap."

Good advice, that's exactly what I had to do earlier this year.
Good luck,
Brian

 

check the sensor at the bottom of the expansion tank, they can come loose and fall down about 2 inches and cause this. I have had sucess super gluing them back on, 2 minute job