Can anyone tell me what an average opening temp on a thermostat in a petrol engine is?

IIRC Fords opened at about 92 degrees - although if you got the QH replacement thermostat that opended at about 88 degrees.

I think the Elise waits until 97 degrees my mate said?

I'd go with 90 degrees as an average though?

Anywhere between 85 and 95 deg is normal. Though there are cars out there with temps outside that range.

Cheers guy's, brother in laws Omega V6 is running at between 70 and 75 all the time,
i'll stick a stat in it just in case