Can some one tell me what the motor temp guage is reading?

Is it reading 90C or 100C or?

I've assumed it is 100C and being a 603 #14 head I've been generically worried about running too warm. For example drove accross the AZ /CA desert last week (HWY 10) and with the AC on and 94 to 100 F ambient temps with the needle floating around the mid line mark. Over a tad upgrade and lower down grades.

Thanks

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1986 300SDL 440,xxx