2001 GMC C6500 Topkick Engine: 8.1L V8; Standard Rotation; Severe Duty Thermal Fan Clutch;. 2009 GMC C6500 Topkick Engine: 8.1L V8; Standard Rotation; Severe Duty Thermal Fan Clutch;. 2002 GMC C6500 Topkick Engine: 8.1L V8; Standard Rotation; Severe Duty Thermal Fan Clutch;.