Seaweed Belongs in the Ocean, Not Your Engine

A little seaweed can cause a big problem. Photo by Peter Nielsen

We were maybe a quarter-mile from the mooring, motoring slowly home on a still summer evening, when the piercing bleat of the engine cooling-water alarm made us all jump. I looked over the side: Sure enough, the flow of water out of the exhaust had ceased. Once back on the mooring, it didn’t take long to pin down the culprit—a plug of weed in the seawater intake for our freshwater-cooled Yanmar 2GM diesel engine.

For some reason known only to Yanmar, the cooling water inlet tailpipe on the saildrive leg takes a 3/4in ID hose, while the inlet to the raw-water pump takes a 5/8in ID hose. The weed had caught in the adapter I used to connect the two different hoses. It was another lesson for me. For some years now I’ve been meaning to install a seawater strainer, but never got around to it. If I’d had one, the problem would have been instantly visible and quickly resolved. A strainer is now near the top of my punch list.

But here’s one thing I had done right: I’d installed a Globe Run-Dry impeller, which reportedly can run dry for up to 15 minutes without self-destructing and bunging up your engine’s heat exchanger. Since we were only five minutes from the mooring when the alarm went off, it gave us plenty of latitude.

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