Wierd Mk3 Overheating problem

Hi all.

I have a VW MK3 1.4l Golf (1994).

I haven't allowed it to overheat as of yet, but it consistantly wants to.
If the car is sitting idling then after about 15mins the temperature gauge constantly goes up until it reaches the overheating point, the radiator fan also does not come on. If i sit in the car (whilst it is still stationary) and keep my foot on the accelerator at around 2-3krpm then the temperature gauge actually goes down to the required midway point.
Both pipes leading to the radiator are not very hot. The top one is luke warm whilst the bottom is cool. There is also nothing wrong with the fan or fan switch, as the water in the radiator part does not become hot enough to turn the fan switch on (and i have tested them).

Also, when the car is idling and the temp gauge is rising near to the overheating point, then the blower heater temperature goes cold. When I rev the car so that the temperature gauge goes down to mid-way again the blower temperature becomes hot like it should do.

The only thing I can think is that the water pump has had it, but is not completely dead as when the engine is reved the temperature gauge goes down, can it possibly be sticking at idle?

Can the thermostat somehow be causing this?

Many thanks in advance for any help you can give me on the matter, it's driving me nuts!

Andy

P.S forgot to mention there are no leaks, no radiator blockages etc..

Sounds like a bad thermostat.. Usually go bad on older higher mileage cars.

well it could be the impeller on the water pump they seam to collect crap from the system and gums up the impeller there for it will still spin quiet but wont actuly pump the water round to cool your engine block i have a simular problem with my mk 3 golf gti 2.0 its fine while going along but stop in traffic and it chucks the water out of the header tank hope this maight help
:banghead: