Mk2 GTi Temp Problem

[pnwrs2000]

Hi, I've got a mk2 golf gti as my daily but it's got an annoying problem with the cooling system: -

The temp gauge will sit at half way normally but for no apparent reason it'll creep towards 3/4's. When it does this the red light starts flashing and then the fan cuts in. The temp, according to the gauge, will then move between 3/4's and just over half. This happens in all weathers.

The heater is only ever lukewarm.

So far all I've done is change the thermostat but this hasn't made any difference. Could a partly blocked / knackered heater matrix cause these problems ? Or possibly a failing water pump maybe ?

Cheers in advance

Darren

[dragonfly]

Does this help: http://www.golfgtiforum.co.uk/index.php?topic=106380.0

[pnwrs2000]

Mmm sort of. I'ts already got a blue cap on the header tank and I went through the steps described a few weeks ago when I thought it might be an air lock of some sort but it all seemed fine.....

[Sgt_Lemon]

Run your hand over your radiator when the engine is hot to see if there is a difference in temp anywhere. Just to check for blockages or partial blockages in that section. Are you also running a good coolant mix, if it's hitting a lower boiling point the temp will raise as it turns to a steam.

[pnwrs2000]

The bottom rad pipe is cooler than the top one. The top pipe is also firmer than the bottom one.
After looking at the rad, it's got some age about it so think I'm going to replace this to start with