Mini One 57plate loosing coollant

[Rogers gang]

can anyone help me please, my Mini One is loosing coollant but only when I am driving, I can leave for 7hrs while at work or over night and it doesn't loose any, this only happens while I am driving, I am having to top the bottle up every night. Does anyone have ideas what wrong.

[smn159]

Expansion tank cap?

[Boogs]

If it were losing water at that rate through the cap I'd expect it to be visible. I would be more inclined to think that it is only losing under pressure and possibly post thermostat. Get it up to temperature so the rad is hot and work your way around the circuit. If not visible then get a garage to pressure test it for you..

[.richard]

Had the same on our 57 mini one. Turned out to be thermostat housing.

[Rogers gang]

Hi, thanks all, we seam to be loosing it from the back of the engine, just seams to drip out when the engine is under pressure