1983 D24T running warm

[VolvoGabe]

Hi all, I have a 1983 760 Turbo Diesel that seems to be running warm at the moment.

I first bought it in January of this year and drove it 1100k's home. For a car that hadn't been started nor driven in 10 years it could not of ran better, apart from it liking to get warm - which was indicated via the temp gauge. The running hot when I first got it probably didn't good more than bad as it allowed the engine to blow out a lot of crap for sitting for 10 years, and god did it. From a gutless smoking freight train to a non smoking peppier sedan it loved the drive home.

I inspected some of the cooling system when I got home. The metal radiator was 3/4 blocked and that's all re-conditioned and installed back in the car. The car had no thermostat, and it still circulated as all the hoses and water in the expansion tank got warm. However, it now has a 90 degree thermostat and re-conditioned radiator but the reading on the temp gauge still climbs to what it was when I first drove it which is just over 3/4 high. The water doesn't seem to be circulating as when the temp gauge reads high, the bottom radiator hose and the expansion tank water are both vaguely warm/cold. Water pump condition is unknown, temp sensor condition is unknown.

What also confuses me is when I turn it off and leave it for a minute, and then start it back up the gauge reads just under half, and then when I start driving it around it goes back up.

Has anyone had any problems like this? Any help is appreciated. Thanks