Jasoncmor

Hi all.

I have a minor issue with my car overheating while driving, never into the red, upto about 3/4 before going down again.
Car is a mk5 fiesta zetec - s.
Cooling system has been perfect since I've had the car, about 8 months ago, the thermostat housing warped and leaked coolant everywhere, so bought a new genuine Ford one, and also replaced the thermostat at the same time, again with a genuine Ford one, then filled up with fresh coolant.

All was fine up until here.

Then recently, I replaced the cambelt, waterpump, and coolant temperature sensor, and heater control valve, all genuine Ford parts again, now this is where I'm having trouble. It had airlocks all round the cooling system for some reason, and in the end, I drained the coolant, and used a garden hose and flushed every pipe I could going into the radiator, the block, the hcv & heater matrix and eventually it was working fine.
I bled by running the engine for about 20 mins, with the heaters on full and squeezing the pipes, I thought all was well.

Now, I've just been on holiday and have driven the car almost 800 miles this week, and occasionally the temp needle has been rising to about 3/4 then falling back just below centre, then back up to centre where it will sit for ages before rising again.
I've noticed when driving slow with the windows open, sometimes the cooling fan has been turning on, on both low and fast speeds, even with the needle at half way.

While I was away I tried to rebleed the system twice, cap off with engine running, and squeezing coolant pipes, yet still the same thing is happening.

I noticed with the engine running and the heater on full, the top radiator hose was cool, the same as the thermostat one, as soon as I turn the heater to cold and leave it for a few mins, the cooling fan then kicks in after 5-10 mins on low, and then the top radiator hose was boiling.

The expansion tank cap is also working fine.

I have no idea what to do anymore, does anyone know things I can try?

Many thanks

Jason