2001 XK8 with/55K miles. Frequent low coolant indicator issue. Had the system pressurized and a cracked t-stat housing was diagnosed. Replaced housing (with a metal unit), replaced t-stat, pipe, O-rings, new coolant, the works. A week later, the indicator light comes on again.

Where else should I look for trouble?

 

Overflow tank topside near the firewall. There is a coolant level sensor inside. It malfunctions, and provides an erroneous signal regarding level. The fix is a new tank. g.

 

Thanks. I'll check this out . But the coolant level was, in fact, down a bit. I've topped it off and will watch it for a while.

 

Look at (or inspect yourself) the water pump also after you check the tank. I also had a tank failure, or better yet, a crack. The water pump was dying and weeping coolant. Since replacement, no monthly low cooling warnings. yeah!