LO 11-8 Outline maintenance procedures and identify tools and methods used to perform maintenance on a diesel engine cooling system

1.16. Evaluating Thermostatic Fan Clutches

Evaluating Thermostatic Fan Clutches
Checking by hand the amount of drag the thermostatic fan clutch has will not provide any indication of whether the clutch is operating. To evaluate these silicone fluid, thermostatic fan clutches, the amount of slippage is measured. This is best done with an optical tachometer. OEM specifications provide a specification for the percentage of the fan speed relative to engine speed when the engine is cold. This percentage increases proportionally to the temperature of the thermostatic fan clutch. Measuring both the fan speed and the engine speed with the optical tachometer will yield accurate data. Visually inspect the fan hub for any damage, looseness, fluid leaks, bearing noise, and missing or broken bolts. Any silicone fluid leakage from a hub or damaged hubs require replacement.