The gauge sensor doesn't follow the curve used to describe the engine coolant temperature sensor for the fuel system.
The green book specifies 10% tolerance for nominal 282 ohms at 122F, 60 ohms at 212F, and 40 ohms at 248F.
I've made some notes years ago you may find helpful or confusing as hell.

The "test" of the gauge prescribed by Volvo is to substitute a 68 ohm resistor for the gauge sender and expect 3/4 deflection of the gauge. I think 100 ohms puts it right about center, what folks call 9:00.

Check the open-circuit voltage at the end of the yellow wire pulled off of the sensor terminal with key on. Should see 10.0V. Start motor, should still be 10.0V provided by a solid state regulator in the cluster.
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Art Benstein near Baltimore
A bicycle can't stand alone because it is two-tired.
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