I wish my issues were as simple as a radiator.

With a brand new thermostat, the results are unchanged............the engine will typically run 95-99C. under decent loads. The infrared gun verifies that the output water from the thermostat is at 82C., but the cylinder head at #2 and #3 is right about 90C.

The engine temperature is unrelated to ambient..........doesn't matter whether it's 100F. or 40F. It's strictly load related.

I'm thinking that the sending unit........close to #3.........is reading the higher temps. generated by these two cylinders.