Hi all, Just seen this thread. I posted something similar on here as well but at that time I didn't know how expansion tank was getting empty. After catching it in the act i was able to see that coolant was leaking from tank. In my case its also a Leon FR 14 plate 184 version (Diesel). What happens is that, coolant is rising it self past where I originally fill it up to. It is going past the max line and, as it keeps going up; the safety feature which is the release valve kicks in and the coolant escapes. I monitored it twice when coolant escaped. I filled it up quite less than max second last time and it overflew by it self and escaped. And then I filled coolant back up but just at minimum. It has however not leaked yet and its been like 3 weeks. I am having to open up the cap on the tank and letting pressure out and then closing it again. I think this is helping the cause and preventing it from over flowing. But aside from that when I go anywhere more than 15-20 miles the coolant leaks out regardless. I paid over £200 to get the car tested. The tank and cap have been replaced. And the tests were done by a VAG specialist. They ran tests on the EGR cooler, which came back negative. They have ruled out EGR cooler and they have said that it wouldn't be the heating matrix with these symptoms. Also the water pump was replaced by SEAT in March this year. Only thing they can say it most likely is, the head gasket or crack in engine block. But keeping in mind that I have had the car since end of June and it runs fine with no dashboard lights coming on. Any words of wisdom anyone?