Its probably fair to say that the objective of the various cooling system components (rad, rad fans, thetmostat, sensor) is by working in constant to achieve and maintain the engine core at a near constant temperature optimal for efficient working and longevity. I imagine then that the thermostat (which is a dumb device working independently of the engine block sensor) opens where required to allow coolant through the radiator and closes to avoid overcooling. For the rest the block sensor will trigger rad fans to enhance airflow through the rad if the dumb circuit is proving insufficient (e.g. stationary car + hot day etc.). A clogged radiator will also invoke the rad fan circuit sooner. Cool bottom (rad exit?) hoses probably thus don't tell you whether the thermostat has opened or not , but hot ones tell you it has.Simon Jones wrote: The temperature will be lower once the vehicle starts moving as the air flows thru the radiator. On my V6 at motorway speeds, the coolant leaving the radiator can be up to 30C lower than going in.
Scavenger fans serve a completely different purpose although i'm sure they are useful to a limited extent as a device of last resort where the proper engine core cooling circuits are not coping.
If i've got any of that wrong please correct me!
