Part Type: Engine Cooling Fan Clutch. 1988 GMC C3500 Engine: 5.7L V8; Reverse Rotation; Optional Standard Duty Thermal Fan Clutch; Fan Mounting Holes are 10 mm.;. 1989 GMC C3500 Engine: 5.7L V8; Reverse Rotation; Optional Standard Duty Thermal Fan Clutch; Fan Mounting Holes are 10 mm.;.