Well Woody, I installed an 80*C T-stat, purchased through FastLane. I do know that prior to my cooling system work, I could drive 200 miles non-stop and the gauge would read 40*C. I figured T-stat stuck open.
What I found was 100% (or nearly so) coolant and a T-stat that had holes drilled all around the lip. Same as having no T-stat at all. Upon replacing the T-stat, coolant and hoses the gauge sits 99.9% of the time at 80*C and creeps to ~82*C in traffic with the A/C on.
With the 80*C T-stat I have I fully expect to see 80*C at the gauge. I think the gauge is nearly accurate, although I don't have access to a laser or infrared thermometer to verify.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.