C5 confusion

Last few non winter months I drove my C5 and coolant temp would get up to and stay around 190-210 F.

This spring I dug out this mystery machine and coolant temp gets up to and stays around 160-180 F

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Do we think thermostat is stuck open or is this normal behavior considering outside temps are cooler? Temps outside have been in 50s and 60s where as during previous times, temps outside have been summer temps - 75-105

I get the fact that it’s cooler out, but gasoline burns and makes heat so car should run around same temp all the time. After all, when it’s stupid freezing outside, my other car doesn’t operate at negative temp