Marshall, first - what Danny said. Assume nothing.
There's little quality control in these replica gauges, so every one is different. And where the sender is mounted on the engine will make a difference in how the gauge reads.
That said, I made up this diagram a few years back when this subject came up. With no 'scale' marked on my gauge, I've taken to interpreting the readings about like this, after driving the car for a few years and measuring the oil temp with a thermometer in the dipstick hole.
And, after watching others post photos of their gauges, this seems roughly in line with what most folks are seeing, too.
PS: I have a manually controlled fan on my external oil cooler, thus the reference to 'turn fan on'.
Cheers!
