B3 1.6 TD temperature problem

[rikdogguk]

So i bought my first passat a couple of weeks ago - 1992 1.6 TD estate... Seems a good solid car so far but having a bit of a problem with the running temperature. Symptoms are as follows:-

- temp gauge pegged at bottom during normal driving.
- can get it up to temperAture by holding revs when stationary... Fans kick in normally at 90 degrees. Cools back down to zero v quickly when start moving again.
- no loss of coolant, bubbling, boiling etc.
- heAter blows hot - even when gauge indicates cold (weird)
- both top and bottom rad hoses are hot when engine is at 90 degrees. When temp gauge showing cold, top hose still hot, bottom hosem coolish.

I have replaced coolant temp sensor, flushed coolant and replaced a leaky oil cooler. Am thinking thermostat might be stuck open, but not sure why heAter would still blow hot when engine shown as cold???

Am new to these cars so would be grateful for any suggestions / coments on what might be wrong???

Cheers, richard