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It is a commom misconception that the fan and shroud do nothing at hiway speeds. This is untrue. At highway speed airflow tends to stall and get turbulent in the grill area, the fan, which is more efficient because it has a shroud, provides a low pressure area to pull the air through the radiator, instead of allowing it to spill out under the car and over the radiator yoke. Ask anyone who has ever towed on a grade at hiway speed and see if their temp started creeping up, then you hear the fan clutch engage and watch the temp come down. This would not happen if the fan did nothing at hiway speed.




IF the fan and shroud are so great at highway speeds,why does the temp on any car increase at slow speeds..This negitive air pocket at highway speeds is pure rubbish...stick your head out the window and spit forward and see if there is a negitive pocket to stop the snot from coming back.

Shroud was designed to help the fan capture and pull air through the rad at slow speeds....a clutch fan does zip at high RPM..it slips..like a clutch...at slower speeds it engages and does it work with the help of the shroud. Thats also why a fan is ideally placed half in/half out of a shroud for optimum efficiency. Slow speeds...fan helps cool...fast speeds..wind/mother nature does it's thing