Saturday Mechanic - Fan Clutch Replacement

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KEYWORDS

• maintenance
• Saturday Mechanic
• transmission

GET PHYSICAL
Check for slop in the clutch. With the engine off and the fan stopped, try to rock the fan blade fore-aft to feel for free play in the clutch. Don't confuse this with flex in the blade. If the fan moves half an inch or more, something's wrong inside the clutch.

You also can check fan speed with a photo-tachometer, an inexpensive tester that is used when a conventional tach can't easily be employed. The photo-tach uses an infrared beam, aimed at a strip of tape, usually attached to the edge of a spinning fan blade. It's worth using if the manufacturer provides any specs, even approximate. On some late-model Jeep Grand Cherokees that have both a special clutch fan and a separate electric fan, the factory spec is just 300 rpm max with the engine cold. Here, the electric fan is a major contributor to engine cooling. On other systems, with a cool engine, you'll find fan speed at about 1250 to 1500 rpm when the engine is revving at 3000 rpm. At high coolant temperatures, the fan speed will rise to about 2100 to 2500 rpm with the engine revving at 3000 rpm.

MAKE THE CHANGE
Begin by separating the clutch from the fan. On most domestic-brand pickups and SUVs, the fan is held to the clutch by a circle of screws or bolts, and the clutch is threaded onto the water pump pulley by a large nut. On many imports, four or five bolts hold the fan to the clutch, and four or five hold the clutch to the fan pulley.

Before you unbolt anything, look at the fan pulley and the routing of the drivebelt. If it's a serpentine belt and wraps around the pulley from the underside, it's probably spinning the fan in reverse. Be sure you get a matching replacement, often marked "Reverse."

If you're lucky, there may be enough room to unbolt and remove the fan and clutch without taking off the radiator shroud. More likely, you're going to have to remove the shroud. This means draining some coolant, disconnecting the upper radiator hose and sometimes removing the belt.

If the clutch is held to the belt pulley hub by screws or bolts, use a plumber's strap wrench to keep the pulley from turning while you loosen the screws. If they're not very tight, you may be able to get away with just pressing on the belt.

If the clutch is held by a single-nut mount, employ a tool that uses the pulley screwheads for restraint. There are inexpensive wrenches designed specifically for this job. Check with your auto parts store.

Reverse the order to install the new clutch. When handling the clutch, lay it flat with the seal facing up to be sure that no silicone leaks out.

GOIN' ELECTRIC
You may be tempted to drop the clutch and install an electric fan kit. If you're taking a street car to the track on weekends, the extra power might get you a trophy. But if you're just fixing the family car, remember that a vehicle maker can integrate electric fan controls into the powertrain computer for a more precise result than you could ever get with an aftermarket kit.

Click to enlarge
Buy or rent any special tools necessary to loosen the clutch from the water pump.