Coolant flow
Heat travels to lesser heat.
Try standing outside on a 10° day. The 98.6° heat in your body will easily move to the outside air temp of 10° (F).
Now try standing Outside on a 90° day. Any body heat over your 98.6° body temp is going to have a hard time excaping from your body.
This is a overheating situation, same applies to cars.....
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