Radiator cooling fan clutches are critical components of most modern engine cooling systems, and while these components are generally not prone to unpredictable or unexpected failure, they do wear out, and need to be replaced without delay when they do fail to prevent the possibility of engine damage.
Function Of A Fan Clutch
The function of a fan clutch is to provide a mounting interface for engine driven radiator-cooling fans, and to allow variable-speed operation of the radiator fan.
Engine driven fan clutches typically consist of a hub that attaches to the water pump and an outer casing that encloses the hub and is attached to the fan blades. In most fan clutch designs, the inner hub is driven by the water pump, and it rotates independently of the outer casing that is partially filled with oil. Attached to the front of the outer casing (closest to the radiator), is a metal element that deforms in reaction to the heat of the air that flows through the radiator core, and over the fan clutch casing.
When the airflow exceeds a predefined temperature, the metal element deforms, altering the oil flow within the casing. In doing do, it commensurately alters the rotational speed of the casing and attached fan blades, thereby increasing how quickly your fan is spinning relative to how hot your engine is. If the temperature drops below a certain point, the metal element relaxes, altering the oil flow to slow the rotational speed of the fan to avoid energy loss or overcooling.
If the fan clutch is fully functional, this cycle is repeated automatically in direct response to changes in the engine coolant temperature.
We should also note that some modern cars have electric engine fans, which means that these vehicles typically don’t have a fan clutch due to the lack of a mechanical fan.
Common Symptoms Of A Faulty Fan Clutch
At very low road speeds and at idle, the regulation of the engine’s temperature is wholly dependent on the operation of the fan clutch. Thus, if the fan clutch does not engage for any reason, the engine coolant cannot shed its heat efficiently because there is insufficient airflow through the radiator core, and serious engine overheating is the inevitable result. This is most easily noticed by watching your temperature gauge, which will climb at low speeds or at idle. In certain vehicles, this may trigger a check engine light which can be diagnosed with an OBD Code Reader. In the worst cases, this can manifest as engine damage secondary to an overheating condition.
Excessively Noisy Fan
If the fan clutch does not disengage it can run at full speed constantly, which can cause the fan blades to make a very loud, and continuous “whooshing” noise that can be audible from the cabin of your vehicle. Moreover, if the fan rotates at engine speeds for extended periods, the excessive speed and vibration can potentially damage the bearings in the water pump, with potentially fatal consequences for the engine should the water pump fail due to a seized bearing and cause overheating.
Increased Fuel Consumption and Loss of Power
Since a defective, fully engaged fan clutch adds considerably to the total amount of parasitic drag on any engine, and particularly so on small-displacement engines, fuel economy can suffer measurably. Similarly, increased parasitic drag reduces useable engine power and can make an engine feel sluggish.
Excessive Free Play
Damaged or worn internal support bearings cause excessive free play between the fan clutch hub and the casing, which sometimes causes excessive noise and vibration levels that can lead to water pump failure.
Replacing A Fan Clutch
While replacing a fan clutch can often be done on a DIY basis, some designs require special tools to unscrew the hub from the water pump, although procuring these tools can still result in a significant cost savings over taking the car to a professional mechanic. In many cases though, the fan clutch hub is bolted to the water pump with small bolts or nuts, and in these cases, the job is relatively straightforward with regular tools.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – Ensure the engine is cold to prevent burns and scalds. In most cases, it is advisable to remove the fan shroud on the back side of the radiator that encloses the fan to give you more room to work. This can often be done using a set of combination or open wrenches, or even by hand depending on the type of fasteners used to attach the shroud. Place the shroud and its retaining screws/clips aside.
Step 2 – Locate and identify all tensioning devices on the drive belts, and use suitable tools to relax the tensioners to create some slack in the drive belt. Failing to do this could make it very difficult, if not impossible, to loosen and remove the fasteners on the fan clutch hub. This will most often require tools contained within a basic socket set.
Step 3 – Remove all retaining fasteners holding the hub onto the water pump, and place them aside. Remove the old fan clutch from the engine, and transfer the fan blades from the old fan clutch to the new unit. Make sure all fasteners are tightened properly, but do not over tighten. This can be ensured by using a properly calibrated torque wrench and following the torque specifications provided by the manufacturer.
Step 4 – Reinstall all parts in the reverse order of removal, but take care not to overtighten any fasteners on the hub. Doing so could cause the new unit to vibrate which could lead to premature failure of the fan clutch or related components.
Re-tension the drive belt, and make sure that all fasteners are tightened properly to prevent belt slippage and possible engine overheating. Reinstall the fan shroud, and make sure all fasteners on the belt tensioner are secure before starting the engine to verify the repair.
Best Fan Clutch Brands
Hayden‘s replacement parts are great and often exceed OEM standards in terms performance, reliability, and fitness for their intended purpose. Moreover, each product line is rigorously tested under normal and extreme operating conditions, which should give you a vote of confidence that your new fan clutch will provide reliable service no matter your application. Overall, if you choose to replace your fan clutch with a Hayden part, we are confident that you will be in good shape.
Click here to find a Hayden fan clutch for your vehicle.
GMB is an OE supplier to major brands such as GM, Nissan, Mazda, and Hyundai amongst others. As such, GMB takes their commitment to quality and customer satisfaction very seriously. In fact, GMB is a globally recognised leader in terms of the quality of the parts they design, manufacture, and supply to the aftermarket parts industry. We have found their parts to be of consistently good quality and can give them a solid recommendation.
Click here to find a GMB fan clutch for your vehicle.
Four Seasons uses advanced manufacturing processes to ensure that only high quality and high reliability parts come off their production lines. Their parts and components made in their North American-based production facilities comply with, and often exceed OEM equipment in terms of reliability, durability, and ease of fitment. Overall, we’ve had good luck with Four Seasons and suspect that you will share in our positive experience with the brand should you choose to use them.
Click here to find a Four Seasons fan clutch for your vehicle.