Those are actually very good results Compugeek.
The cooler seems to be keeping what is inside it somewhere between 26 and 40 degrees cooler than the high temperature in the trunk of your car.

Would I be right to assume the cooler was fairly empty, and that if it was full the thermal mass might keep the stuff inside even cooler?

Or would that be incorrect and it would not matter much?
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May set off to explore without any sense of direction or how to return.