Moss Motors, Ltd

New water pumps can at times leak when first installed, the leak being discovered prior to the startup. This can be a frustrating experience, particularly if you proceed to remove the new pump in order to send it back to your supplier for exchange!

The usual cause of a leaking pump is due to the carbon race water pump seal not fully seating against the back face of the impellor. Since the hard carbon sits against the cast iron or brass impellor with only light spring pressure, it shouldn't be difficult to believe this to be the source of the leak. The best way to insure that the carbon race is properly seated, is to actually spin the pump prior to installation. I do this very effectively by holding the impellor against the wire brush side of my bench grinder. Spinning up the dry pump for 15-30 seconds insures a good lapped seat. Alternatively, new pumps can be installed, but be sure to start the engine without coolant and run it dry for 30 seconds or so. The coolant acts as a lubricant and actually inhibits this important seal break-in procedure.