Diesel Turbo Thermostat

[Super-G]

Took my thermostat out today and tested it in hot water. It does opens and closes at about the right temp, so I've put it back in. But the temperature gauge still doesn't really sit as high as I thought it would. The temp gets up to about 75 then drops back down to 70. Put my foot down a bit up a hill and it did creep almost up to 80 for a brief moment, but was back down to 70 odd in no time.

So the thermostat's working fine and I'm just not used to seeing such a cool running motor