well, the temprature sensor has decided it wants to read full all the time no matter what, engine cold, engine hot!

Is there a chance there is something shorting out.

when i disconnect the sensor the gauge goes down and then i connect it up again and straight back to full?

could be earthing out, gauge will go straight up if you put it to earth if i remeber correctly, but i reckon its the sensor, got another one, just swap it out...