Don't Underload Your Diesel Engine

I have been around boats with diesel engines for more than 40 years. In that time I have heard many times that we should not run a diesel engine under light loads for long periods because "it can glaze the cylinders". Another statement has been "diesel engines like to be loaded". Maybe you have also been told or read this but do you really understand what is going on with your diesel, why it is so important to run it with healthy loads and why you should not over-power your boat?

A turbo charger turbine wheel fouled with soot and fuel, the result of chronic underloading. This gunge also fouls your upper cylinders, exhaust valves and exhaust system. From there it is washed out with the cooling water into the water on which you enjoy your boating. Photo courtesy of Steve D'Antonio.

I am a proponent of reasonable size motors in sailboats but often deal with owners who want to put much bigger motors in their boats than I recommend. My 36ft boat had 20hp, my 34 had 12hp and my 38 footer had 18hp. That 12hp could push my boat against a 40 knot wind on flat water. Sure, it was slow progress and the motor was working very hard but it could do it. In less extreme conditions the motor wasn't just ticking over to move her at reasonable speed. A 20hp motor would still be acceptable on that boat but anything bigger would be over-powering it.

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