Ruby needs help again

my sisters XJ6 ,Ruby, has a problem of heating up and losing coolant over by the drivers side front tire area. I havent seen exactly where its coming from ,because she lives 7 hours away. When I replaced an exhaust valve in the 4.2l., I did not replace the thermostat.I could loosen 2 of the 3 bolts,but i feared breaking one bolt off. Could it be that a faulty stat would be the culprit causing the problem? there is an expansion tank ,I believe right up by the drivers side front tire. Any help from you good people will help . Karen has ruby at a garage for a look at the situation. thank you ,Mark

There’s a catch tank in front of the front wheel that can overflow when the owner keeps topping up.
If it keeps losing large amounts of coolant she has to do something about it. The engine gets hotter after shutdown so this is where leaks show up and also where the systems stabilize after a refill. As long as she can still see any coolant in the reservoir she’s on the safe side.

A faulty thermostat will show on the gauge. She can also check if the hose is
Hard immediately after start up
Getting hot after driving for a bit (by then it will be hard because the pressure has risen either way).
She can also disconnect the line at the cap of the reservoir and see how much coolant comes out there when the engine is hot. Maybe the cap is not sealing well anymore and a little coolant escapes all the time.

Adding to David’s sage advice, Mark. If the thermostat works as it should; the gauge should read thermostat operating temp, warmed up engine, in about 5 minutes of driving. If longer time is required the thermostat has indeed failed - and you have to ease that pesky ‘third’ bolt out to change it. Which is an operation we all approach with trepidation…

A failed thermostat cannot cause a leak, but as David says - if the owner adds coolant; excess coolant is expelled. The recovery tank in the wheel well may overflow, but equally it may be omitted/missing - and the overflow spills on the ground, imitating a leak…

xj6 85 Sov Europe (UK/NZ)

The catch can and/or hose is leaking.