MGZT coolant problems
Hi Guy's i am a new member so bare with me, but need some advice with my 1.8 K Series MGZT 120+. My car is an 04 plate with 98,000 on the clock and with the usual issues all fixed head gasket, fuel filter, all this has been done over the life span of the car and all seemed well, but over the last few weeks my car has started loosing coolant through the expansion tank cap and is doing the same through a brand new genuine rover one as i thought it might be the old one had failed. The interior heater is working as it should, the car is not overheating only when it has lost most of the coolant and then the fan kicks in as it should, i immediately stop let it cool and fill the system back up. I check the water level every day, the level stays fairly constant but under pressure sometimes when cold and overflowing from the expansion tank when i remove the cap after the car has stood all day which i know is not normal, the problem usually starts when i am in slow moving traffic. I have had a mate who is a mechanic look at it but the car fails to play up every time he has it for a day so both of us scratching our heads, i really don't want to get rid of it as this is the best car i have ever had and i am hoping it is something simple any ideas?