Im ? I wander why water is circulating slow through heat exchanger . Whole new pump this time !  $70 parts . 45min of my time to replace !! A piece of gum bark perfectly covered the inlet !! Impeller needs water to lube and cool !!  Thinking of adding a fail safe self priming pump ? Have engine protector alarm on oil / coolant temp . I dont break things a little !  400hp river , skii boat LS2  6litre engine . 55 knots is fast on water !!