> The U.S. (Fahrenheit) models have a middle mark at 185
> degrees and an
> upper mark at 250 degrees; however, the metric (Celsius) models have a
> middle mark at 70 degrees and an upper mark at 100 degrees.
That may be true for some gauges, but certainly not all of them. The
TR2/3/(early 4 ?) Fahrenheit gauge reads to 230F, while the Centigrade one
reads to 110C. I also have an NOS aftermarket Smiths that reads to 230F.
> Obviously these
> numbers don't match up in a straight conversion (185F = 85C; 250F = 121C;
> 70C = 158F; 100C = 212F).
No reason why they have to, the gauge movement can easily be recalibrated,
and there were even different sending units for different applications, with
apparently different resistances.
> Does anyone know why the metric temperature gauge
> is scaled like it is?
Sorry, no idea unless perhaps it was targeted for a cool climate. Are you
sure you're looking at an original TR4 gauge ? I see the drawing in the
SPC, but they aren't always accurate. And my TR4 handbook only has a photo
of the F gauge.
> It would seem to me that a running
> temperature of 70C
> would be a little on the cool side (158F), yet it's the midpoint on the
> gauge, and one would typically assume that the midpoint on a temperature
> gauge is the target operating temperature of the vehicle.
I agree. Even more worrisome, one would expect the top of the scale to
cover at least the boiling point of the cooling system. Even with no
antifreeze, the radiator cap will raise the boiling point above 100C.
Randall
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