1979 GMC G1500 Engine: 4.1L L6; Standard Rotation; Optional Non-Thermal Fan Clutch; w/ A/C;. 1979 GMC G1500 Engine: 5.0L V8; Standard Rotation; Optional Non-Thermal Fan Clutch;. 1979 GMC G1500 Engine: 5.7L V8; Standard Rotation; Optional Non-Thermal Fan Clutch;.