During my little rebuild 'project', I replaced the temp gauge sender.

Running it up to temperature I panicked when the gauge went over half way, but became steady around 75%, ie between N and O. I figured that as it was in the 'norm' it was ok - if it was in the red I would've shut it down. The new thermostat appears to open OK, and there's no boiling of coolant, and the fans came on 'about' the right time, and went off again about the right time - but the gauge didn't go below O. From other similar threads i've decided that I've prbably got a crap new temp sender, which i won't whinge about for the sake of a tenner as I can get another one easy enough.

I thought I'd check the resistance of both, cold and hot, and got the following:

Cold: new sender 1.2k ohms, old sender 3.3k ohms

Hot: new sender ~200 ohms, old sender ~500 ohms

From that, I'm thinking that the new sender is basically shorted, at operating temperature making the gauge go high, as if you shorted the connector to earth.

If anyone else could post their readings that'd be great; would save alot of time-consuming troubleshooting for anyone doing something similar.