That was the inflatable grille blocks job.
Restrict air flow to bring the cooling system to the desired AVERAGE temperature. Deflate them when it starts to get too hot, then only add the electric fan after the grille block has deflated for max air flow. Now you are controlling the temperature of the coolant ENTERING the engine after going through the radiator. THAT temp varies greatly depending on ambient temps but this would control the radiator EXIT coolant temperature. Normal thermostats control the coolant temp as it leaves the engine but there is no real control of the temp of the coolant ENTERING the engine.
The hotter the coolant entering the engine the less heat absorbed from the engine, part of why summer mileage is better.
Think of it as varying the size of the radiator to match the ambient temperature.
regards
mech
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