Well so anyways the thermostat seemed to be sticking, from a cold start it would overheat until I gave it a bit of a blat and the temperature guage would settle down to a comfortable 1/4 way mark for the rest of the trip. So I took it out, scratched my head a little at the large pebble that seemed to be jammed in it before throwing it over my shoulder and putting a new one in. Only the engine seems to be running too hot now, in traffic it will sit between half way and 3/4 up the temp guage. What are the chances that a brand new thermostat will be incorrectly set? According to the Tridon website it is the right one for a Holden 308.

Try a cooler thermostat?

Inaccurate gauges, particularly when only indicating Cold to Hot, are only a guide. Using a hand held infrared temp sensor pointed at the thermostat housing will clarify what the actual water temp is at. Or fit a correctly calibrated gauge to the car. Thermostats are available for many temp ranges. Maybe find where old one landed & see what range that was then get one the same.

Utility8