[Russf]

Barnacle Buster is just phosphoric acid, you can check the MSDS and the active chemical is phosphoric acid. Impellers should not be damaged by the acid especially phosphoric as it is a fairly weak acid. Phosphoric acid is what is used as a rust converter or rust remover. Typically the raw water pump is not used to circulate the cleaning agent through then engine. Another pump is used and a closed loop is created to recirculate the cleaning agent around the engine. The impeller is removed if you connected at the seacock side of the impeller housing. 

Thanks Tom. In a 6.0L Crusader the raw water impeller does circulate raw water through the heat exchanger oil and emission coolers, and the risers. That is why I was concerned about the impeller.