Always cold!?

Hi,
Just bought a SWB 90 (1989) that's had a 200TDI engine conversion.
After buying it (same day), the radiator sprung a leak and I replaced the radiator last weekend. taking it to work the temp gauge now, however, just hits the very beginning of the cold reading and never goes above it no matter how I drive it. It was sitting about mid point before but that was with a dodgy radiator so I've never known what the reading was at.

Also the heater is just cool. I've got rid of all the air (I think) which has helped but it's still not great, warm at best.

Could it be faulty thermostat, wrong thermostat. If so could that effect the heating. Could the original sender be there (can I check this?), if so, should I put the original thermostat in the TDI engine?

Any help/suggestions greatly received!

Thanks.

when the thermostat on my disco was faulty the gauge read low and the heating was only warm at best so for a couple of quid its worth a try.

did you bleed the system using the cap at the rad and thermostat aswell? if not it would be a good idea to look there too

Take the wire off the temp sender and ground it to the engine block with the ignition on. If the gauge shows hot then Its either your sender or your thermostat that are faulty.

Run the engine from cold and feel the heater hoses. They should start to get hot while the top hose of the radiator should stay cold until the stat opens. If the radiator hoses warm up at the same time as the heater hoses then your stat is stuck open or you dont have one fitted.

If the radiator hoses stay cold while the heater hoses are warm then your sender is probably naff or it may be the wrong one for the gauge.

It was the thermostat BTW.
Temp sits just below halfway and the heater is nice and toastie.

Thanks for all your help.