Testing a 2002 S-10 Fan Clutch

The fan clutch on a 2002 Chevy S-10 is attached to the water pump through the use of a large nut threaded onto a shaft on the water pump. The fan clutch is a viscous type filled with a silicone-based oil. The fan blade is bolted to the inboard, or engine, side of the clutch.

Purpose

The purpose of the fan clutch is to operate only at a predetermined temperature, which is achieved, for the most part, only at an idle. Above an idle, the temperature transmitted through the water pump shaft drops and the fan is released to spin at a lower speed with very little resistance. The lower resistance frees up horsepower, which translates into increased fuel economy.

Operating Principals

The silicone-based oil in the clutch expands with increased temperature, its friction increases and the fan picks up speed for better cooling. As the truck begins moving, the relative wind passing through the radiator drops the temperature transmitted to the clutch, and it reacts by releasing.

Cold Engine Clutch Inspection

You must perform the initial inspection with the engine off and cold. Look closely at the fan clutch and its shaft for leaks. If the silicone has escaped, it will leave tracks on the shaft or outward from the center of the clutch where centrifugal force throws it. Next, push front and back on the top of the fan blade to see if the bearing is good in the clutch. If the bearing is worn out, the fan will rock back and forth to some degree. Lastly spin the fan by hand. A slight resistance is normal and expected. If the fan freewheels, rocks back and forth or shows evidence of a leak, replace the clutch.

Engine Running and Hot

Start the engine and watch the fan blade speed. At the same time hold a hand over the center of the engine away from the fan and feel the airflow for a second. Let the engine warm up and compare the fan speed and wind thrust to that of a cold engine. As the engine warms up to normal operating temperature, the fan speed and sound should increase noticeably as well as the wind thrust from the fan. Raise the engine rpm rapidly and let them drop back a couple times. Watch the fan. It should not speed up when the engine is accelerated rapidly. If the fan speed rises as sharply as the rpm and makes a loud rushing noise, the clutch sticks when hot and must be replaced. If the clutch fails any of these tests, replace it.