Hi, My 'L' reg 106 XND 1.4 has recently started guzzling a _full_ expansion tank of coolant, every time I take it out. I've discovered that the tank isn't leaking, by simply leaving it over night. However, when I start the car up, a nozzle on the side of the coolant expasnion tank screwcap lets out coolant. This happens within maybe 20 seconds of starting the car, so I don't think it's overheating or reaching a very high pressure. Could the screwcap be faulty, or is this caused by something else? Thanks for yur time.