Hi all, I bought a mk5 1.4 petrol fiesta last week. It was mot'd last month and had a new thermostat, housing and header tank(I think it was). Before the mot. On Thursday evening I was sat waiting for my partner, engine running in neutral for approximately 20 minutes. Next thing I know the engine is smoking. At first we thought the thermostat hadn't been changed, but it has. Checked the oil, water tank seems to be working, there's no leaks around the gasket and it's still driving fine. Engine coolant is fine. It hasn't overheated since but I've literally used it for short journeys and trying not to use it if I can help it. I also sort of lost abit of power in the accelerator about 30 minutes before it overheated. Does anybody have any idea what could be wrong? Would be massively appreciated :)

20 minutes idling seems like an unnecessary waste of fuel tbh.

Does the radiator fan come on when it should?  It is possible that the coolant heated up so much while idling that some had to escape through the expansion cap as steam.

Yeah it is, it wouldn't of been on if my kids weren't in the car. It was freezing cold and they are only young. 

I think it does. 

I have just checked under the car and I have water leaking from somewhere.

Ah ok well if there's water leaking that'll most likely be the cause of the steam.  Unfortunately none of us can say where it's from without seeing it though.  If you can find where its coming from and post a picture that would be ideal. 

Found the cause of the leak, the garage where the previous owner got the work done used a cheap crappy thermostat housing and cross threaded it, that's been replaced. So no water leak, my partner reckons the head gasket has gone, had a small amount of creamy sludge after driving around the block to see if the leak had stopped, but nothing now. But there was abit of oil in the water/anti freeze that was drained yesterday so it's booked into my local garage at 3. So will see if he can find the problem. Wish me luck I think I need it 😂

i know it's not helpful but...

I am in my mid50s and had many many cars. In my long experience when buying a 2nd hand car, if someone says some work has just been done it puts me off. from experience this often means that work has been done badly, or it has been done to fix a fault that was misdiagnosed and the fault will still cause problems or it was a bodge up to make it work long enough to sell it.   If I was buying a car which had just had a new thermostat I would have been thinking does this mean there is an overheating problem due to a worse fault