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How and When to Use an Auxiliary Electric Fan

2012 March 22
by therealcoleq

Is your car running a little hot in traffic or when you're moving slow? Is your truck or RV running hot when you are towing up a hill during the hot summer months?? Consider adding an auxiliary electric fan to help your primary cooling system.

At slow speeds or while sitting in traffic, you have very little or no ram air coming through the radiator, and typically, the engine is running at a lower rpm, which means the belt-driven fan isn't moving much air either. In some applications, this can cause the engine to run hot or overheat because there isn't enough air moving through the radiator.

Adding an auxiliary electric fan to the front of the radiator can overcome this problem. Flex-a-lite makes several fans that have an open shroud design to allow for airflow, which is ideal for this use. Part numbers 112, 114 and 116 range in size from approximately 13-16 inches and create between 1,105 and 2,215 cfm of airflow. Part #119 is a 16x16.5 inch fan that moves an impressive 2,500 cfm and is only 1¼ inch deep at the shroud. These fans can be operated with a toggle switch for manual control (Flex-a-lite #31148), or with Flex-a-lite part #31147 Adjustable Temperature Sensor to automatically turn on when needed, and you can adjust the activation temperature from approximately 180-240 degrees Fahrenheit.

Here are some selection and installation tips to help you get the best results:

  • Find an auxiliary fan that covers as much of the radiator core surface as possible
  • Don't use a fully-shrouded electric fan: Shrouds on the back of the radiator are good, but you don't want to block air flow with a shroud on the front of the radiator
  • Make sure the auxiliary electric fan comes set up as a puller (such as Flex-a-lite part #119) or that you switch the blade direction and wiring if the fan is reversible (such as Flex-a-lite part numbers 112, 114 and 116)
  • If you have an auxiliary transmission cooler in front of the radiator, you may have to move it forward in the vehicle to mount the auxiliary electric fan directly to the radiator core
  • Consider installing a transmission cooler with integrated electric fan (such as Flex-a-lite part #4190) to move this heat source somewhere other than in front of the radiator

We've seen an auxiliary electric fan help many types of vehicles keep their cool. This includes off-road vehicles that are moving slow on a trail, hot rods at big events where there is a lot of traffic, tow vehicles carrying a heavy load up a steep grade  and commercial delivery vehicles that spend much of their time parked and idling.

Visit our electric fan applications page at for a complete listing of fan sizes and cfm ratings to find one that will work best in your application.

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