(T) Overheating - Help please

Hi all, i know this message is long sorry, but i need some advice.

My Sei overheated on the way to work after doing 80-90mph (almost
full throttle) on the motorway for approx 14miles. As i came off the
motorway i could see steam coming out of the bonnet and the
temperature warning light came on so i wacked the heaters on full and
managed to pull into a garage just down the road.
I opened the bonnet steam coming out, slowly unscrewed the cap and
there was some serious pressure, water boiling etc waiting for 1/2
hour filled it up with water again and off too work cautiously.
I noticed there was a load of small pieces of thin black plastic
floating around the expansion tank after i filled it up?!?!?

Come home from work and it did it again as i expected, this time it
seamed there was more pressure built up and there was no water left
in the expansion tank, filled it up with 2 litres of hot/warm water i
got from work and came home and sat outside my house for 5 mins and
it overheated again, i noticed the fan did'nt kick in (Check fuse 2moro)

Surely if i'm doing 70-80mph there should be enough cold air through
the radiator to prevent it from overheating???
I reckon it could be:
1) Radiator cap
2) Blocked pipe - Possibly although i had water coming out of the
carb when i took the pipe off
3) Blocked/Kanckered radiator
4) Head gasket??? - But no smoke/steam/mist out of exhaust, no oil in
the water or water in the oil
5) Thermostat - Either kanckered or blocked from the bits of plastic
floating around the expansion tank

Where abouts is the thermostat and housing on the engine???
Has anyone got a clue what these bits of plastic are??

Thanks in advance, sorry for the long post
Any opinions/advice would be much appreciated


"The Not so Fast but Furious"

Don't worry its all sorted it was the thermostat

"The Not so Fast but Furious"