Hi all, I have been following the forum via the app for a while and have learned a lot from you guys, so thanks to all for the useful info. Any detectives out there feel like helping me out on this one I'd be very grateful.

My first mistake was buying this Mondeo in the first place - I think old rep car from Scotland (bad move), had an issue with the timing belt before I bought it which was replaced because it had been fitted incorrectly before. (second bad move). Dealer mentioned about an overheating issue which they had 'fixed' by changing the thermostat. So last summer it overheated on the M25 (almost no coolant) - I should have taken it straight back to the dealer (another bad move) but took it to my local garage instead. They changed the fan which wasn't working. Overheated again about a week later - this time found the coolant leaking out the thermostat housing. Chicken and egg situation whether previous overheating caused this or not. Ever since the coolant has been disappearing slowly and I have been topping it up every couple of weeks. It's needed less over the winter but now it's warming up I have had it happen again on a long journey (level checked just before leaving, was fine).

It only seems to happen at high speed (60-70) anything below that it can cope with. I think it is coming out of the release valve on the cap of the overflow tank when at these speeds suggesting a pressure issue? The AA and my garage can't find a leak - the water was pressure tested and the needle didn't drop a bit, the water pump is fine, not leaking into the carpets. I know I should just get rid and it's one of those bottomless pit jobs but I'd like to be able to understand what's going on. Any useful ideas? And yes I know it's not probably worth investigating but I'm not in a position to change the car at the moment as with this issue it's next to worthless...

Thanks