We recently replaced the raw water cooling pump on our Cummins 5.9 engine. When we hired a mechanic to change the impeller, he discovered that our spare impellers for the previous pump did not fit the new pump.  THE MECHANIC WHO REPLACED THE PUMP NEVER TOLD US THAT THE NEW PUMP USED A DIFFERENT IMPELLER. THERE WE WERE WITH NO SPARE IMPELLERS.  Two days later with new impeller installed and 3 new spares we are on our way. Jon, Valentine ,Nordic Tug 37