Fitment: 2006-2009 Chevrolet Express 2500 2006-2009 Chevrolet Express 3500 2001-2005 Chevrolet Silverado 2500 HD 2001-2005 Chevrolet Silverado 3500 2006-2009 GMC Savana 2500 2006-2009 GMC Savana 3500 2001-2005 GMC Sierra 2500 HD 2001-2005 GMC Sierra 3500 What is a Fan Clutch? A fan clutch is a thermostatic engine cooling fan that can freewheel at low temperatures when cooling is not needed, allowing the engine to warm up faster, relieving unnecessary load on the engine. As temperatures increase, the clutch engages so that the fan is driven by engine power and moves air to cool the engine. .