Most cars these days have a cooling fan that only runs when needed.The advantages in fuel economy ,warmup time ,pollution,HP are well documented elsewhere.The popular methods are the electric fan and the viscous coupled fan.The basic idea is that the fan runs when the engine is hot and does not when the engine is cold .If the car is running at speed the airflow through the radiator grill increases .At a certain road speed the flow may be enough to cool the engine anyway .What would this speed be ? Would it be worth it to shut down the fan at high road speeds?

  • Does this answer your question? Mar 13, 2016 at 11:41
  • I'm afraid it would change from car to car, but "worth it" for what exactly? The system should already turn on the fan only when needed, as you mention. Mar 14, 2016 at 12:01
  • Auto engineers are going to great lengths to get small improvements in fuel economy .The rotating fan represents loss even when the car is moving at speed .If its not beneficial then you may as well shut it down .
    – Autistic
    Mar 14, 2016 at 12:07
  • 1
    Good question. I think most understand the basics, but i suspect few are considering the grey area or overlap. Once the car is travelling a certain speed the airflow is probably having more effect than the fan, and/or the fan has nill effect. However the fan wont turn off until the temp drops below the fan cutoff point. There may be a narrow window where the fan is running but providing no benefit at all. Mar 15, 2016 at 8:55

2 Answers 2


Since the fan is thermostatically controlled, it will automatically shut off when the natural air flow through the radiator is sufficient to keep the engine cool. The speed at which this occurs will vary based on the car and weather on a given day.

Never heard of anyone disabling the fan. I have heard of people partially blocking the radiator opening in sub-freezing weather to prevent over-cooling the engine.


I remember seeing something about this for the ECU code for the ~83-95 Dodge/Plymouth/Chrysler 2.2L/2.5L FWD cars. The ECUs were engine specific, not vehicle(body) specific. I believe at 35mph it introduced 'delayed cooling' where it would not engage the fans until a later temperature.

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