Can '64 Dart Temp Gauge Be Adjusted?

Bob. Redfish will have a more complete answer but 200 F around the middle of the scale would seem about correct.
These systems operate under pressure. I forgot what the early caps open at, but its something between 11 and 16 psi.
Bottom line is that operating temperatures above 212 F are still normal.
The inside lines probably are meant to indicate the normal operating range, something like 190 to 225 is my guess. Do you have an owner's manual in the glovebox? Might say in there.

I think I took this pic from the owners manual of my '75 Valiant (long gone).
Hot on the gage was 250 F
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