One type of radiator fan is an electric model. This type normally attaches directly to the radiator on either the front or the back. Front-mounted models are known as "pusher fans," while rear-mounted units are known as "puller fans." A pusher fan pushes air from the grille area over the radiator to aid in cooling, and a puller fan pulls air from the grille over the radiator from inside the engine compartment. These electric fans work off of the 12 volt system used by the automobile itself. Many of these fans are thermostatically controlled, meaning that they turn on and off at certain, preset temperatures. Most electric fans will have their own shroud to aid in cooling.
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The other type of radiator fans are engine-driven units, which spin only when the engine is turning, and only at the same rate. Some of these fans, such as on old Ford models, are a "direct drive" system, meaning a solid bar connects the fan to the pulley, so the fan is always moving at exactly the same rate as the engine. Other models employ a clutch, which allows the fan to stop turning after a certain RPM is reached. The fan is no longer necessary at such speeds, because there is sufficient air passing over the radiator from the vehicle motion itself. Another type of fan that cuts out at higher RPM levels is a flex fan. These fans utilise very thin stainless or aluminium blades, which flatten out once a certain speed is reached, which eliminates drag and gives the engine more usable power.
Things to Know
Reversing the polarities on an electric fan could cause it to run backward, so be careful if installing one in the driveway. Never work on a fan with the engine running under any circumstances. They can be unpredictable and dangerous. Never remove fan shrouds to improve the look of the engine compartment; they greatly increase the flow of air from the fan to the radiator. If installing an electric model yourself, it is recommended to hook up thermostatic controls or a toggle switch so that the fan is not running the entire time the vehicle is on.