You probably know that the radiator in your car cools your car’s engine. It does this by allowing outside air to flow through the radiator core thus cooling the fluid circulating inside. The problem is that cars aren’t always moving so years ago engineers designed special fans to physically pull outside air through the radiator. This is an especially important process when a car is running yet standing still -picture getting stuck in a traffic jam.

The first were mechanical

Originally the cooling fans in automobiles were driven directly by the engine. For decades, in fact, they were mounted in the front of a car’s engine and were driven off a pulley connected to the engine’s crankshaft. This configuration worked great except it technically used up a little engine power. This loss wasn’t a problem in the days of cheap fuel, however, when the government started imposing gas mileage requirements on Detroit, the car manufacturers starting looking ways to save gas.

They went electric

Virtually all of today’s cars have electric fans. The main advantage to these is that they can be designed to run at optimal speeds and only when needed. In other words, when driving, an electric fan can be shut off (because it’s not needed) thereby increasing efficiency and gas mileage. And, when stuck in traffic, electric fans can easily be switched on if the coolant temperature rises too high. Another benefit of an electric fan is that a cold engine warms up faster too (because no fan is spinning and drawing air through the radiator).

How they work

Electric cooling fans are mounted right behind the radiator. In older cars, they typically consist of a direct current (DC) electric motor with a thermostatic switch to turn it on or off. With these simple circuits, the thermostatic switch on the radiator connects to battery power on one side, and to the fan motor on the other. When the radiator coolant heated up enough, the thermostat would close the “switch” and the electric fan would start spinning.

According to Reedman-Toll Chrysler of Langhorne, a Chrysler, Dodge, Jeep, Ram dealer in Langhorne, PA, in the 1990s, the circuits got a little more complicated. Engineers passed the fan control function to a dedicated module or the car’s main computer. Typically, a thermostatic sensor is used but instead of it switching a large amount of current, it simply is used to trigger a high-power relay. This allows fans to be switched on when AC systems are being used. This is so they can draw air across the AC condenser.

They still use engine power, though

Which brings up a point commonly misunderstood: electric fans are engine-driven. All the electricity in a car must come from the alternator, which is turned by the engine. Electric fans draw a lot of power and that current has to come from somewhere! And that somewhere would be the alternator. However, the system is more intelligent than the old mechanical fan and fan belt method because it can be turned on and off when operations under the hood require it to.