When the raw water pump fails, which is usually due to running dry, the impeller must be replaced. But wait! You must find and remove the pieces of the failed impeller that flowed down stream from the raw water pump. Until you retrieve these pieces, you can consider the water flow from the raw water pump to be plugged.
This plugging will cause overheating of the transmission, the engine and also the wet exhaust system hoses and related plumbing.
As the above photo shows, this transmission oil-cooler, the first heat exchanger in this system, was eighty percent plugged. Transmission overheating and failure was the result.
After clearing the blockage, the next step is to lubricate the new impeller with mild liquid soap before installation of the impeller. Finally, run the engine for a few minutes to wash the soap from the system.