Green Harbor MA Captain’s Log

The procedure for replacing the impeller outboard motors will vary some based on the manufacturer but there some are tell tale signs when it is in need of replacement. For me it was over heat warnings when trolling at very low speeds (under 1000rpms). Even without a warning system a quick inspection of the telltale stream for signs of cooling impeller failure or weakness is usually all that is necessary. If the stream is weak or nonexistent, first run a piece of wire up the hose to dislodge any sand or debris that may have clogged it. If there still isn’t a strong, steady stream, replace the water pump impeller. Opinions vary on regular impeller replacement. Some mechanics say every two years and sooner if operating in silty water. Others say that unless you’re chewing up the bottom with your lower unit your impeller will last many years. If you install a water pressure gauge you’ll know if pump output is getting weaker. I tend to favor the every two years or sooner approach, as I spend a fair amount of time fishing in the shallows of Duxbury Bay where it is silty and I’ll admit that on occasion I’ve dragged my lower unit through the muck. The way I see it you are better off replacing them impeller than risking more serious overheat damage to your motor.

Once you have replaced the impeller make sure you take care of it. My Mercury 200EFI has a direct hose connection on the motor (as do most new outboards). Every time I return to my slip I flush the cooling system with fresh water. The purpose is to flush out not only salt deposits, but also sand and debris.