1677-HO 1999-2004 Chevy GMC AM Gen 6.5L Diesel CCW threaded fan clutch water pump

The 1677-HO is designed to outperform GM's higher flow rate "130 gpm" pump introduced in 1997 with the threaded hub. GM achieved higher flow rates with a 10% larger impeller diameter than the earlier versions.  Most people simply look for that to determine if it it is higher output or not.  We go a wee bit further. Our impeller outperforms and outflows to help the 6.5L diesel run a little cooler under a load.  The impeller has an increased vane count, a reduced impeller vane clearance to the casting volute and a ported shroud to build pressure in the eye and an appropriate B gap clearance to limit the potential of pressure pulsation or hydraulic shock.  It achieves greater flow rates, higher head pressure and a more efficient flow. The impeller color is due to Type II Class II military grade surface coating which protects against corrosive fluids.  FlowKooler introduced the first hi flow pumps and continues to improve impeller design. Why is increased flow so important to cooling a hot