Boat Engine Troubleshooting

By Tom Neale
Photos by Mel Neale
Published: April/May 2013

What's that funny smell? Do you hear a strange noise? Wait a second, that feels too hot! Stop and trust your senses. They've got some important news for you.

Using your senses of hearing, touch, smell, and sight can alert you to an impending situation with your boat that may be about to ruin your day. Here's how to heed the warning.

Your Sense Of Hearing

Ignoring Whining Now Could Make You Cry Later

Photo of Tom Neale with a mechanic's stethoscope
A mechanic's stethoscope can be used to detect unusual noises in engine components. Here, Tom Neale listens to the turbo.

Some problem noises are obvious. Some are not. Get into the habit of regularly listening to critical components such as the fresh- and raw-water pumps, alternator, transmission, injector pump (if you have a diesel), and any other convenient spots. You'll then have an idea of what's normal. You can use a long screwdriver with plastic handle to listen. Touch the blade to the part and put your ear to the round end of the plastic handle. Far better, buy a mechanic's stethoscope. They usually cost less than $20, and are much more sensitive and safer to use. Keep well clear of the pulleys and belts when you do this.

  • A gravelly noise from a component with bearings can indicate that the bearings are about to fail. The alternator and fresh-water recirculating pump are prime suspects when you hear this. A belt that's too tight could hasten either of these failures.
  • Change in tilt-lift motor noise on an outboard could be a precursor to pump failure or air in the tilt motor fluid. It could also indicate drop in voltage that could indicate fault in the charging system, corroding connections, or wiring. Note: It's normal for most tilt motors to have two different levels of sounds as the function shifts from power trim adjustment to full tilt.
  • Variation in the engine noise, called "hunting," could indicate impurities in the fuel, an air leak in the suction line, a clogging filter, a failing fuel pump, or a failing injector pump.
  • A "thunk" when you push the starting button means problems, even if your engine then seems to start normally. The "thunk" could be caused by a hydraulic lock resulting from water standing on top of a piston. If you hear a lighter "clunk" in the starter, it may be a bad solenoid, engagement gear, or starter.
  • A squealing noise could indicate a loose V-belt, but it could also be a clue that one of the components it is turning, such as the alternator or fresh-water recirculating pump, is freezing up. Bad bearings could be causing this in both components. Overload or deteriorating internal parts could cause this in the alternator.
  • Unusual cracking or creaking sounds when hitting seas, running at speed, or otherwise stressing the hull could indicate delamination, structural bonds failing between bulkheads or supports, impending transom detachment, or other serious problems.
  • The bilge pump running more often than usual means you should start looking for a leak. Some less obvious sources of water in the bilge include the propeller shaft seal, the freshwater system, the cooling system, the pop-off valve in the hot water heater, and the hoses on the engine.
  • Unusual noises in the transmission usually signal a problem developing that could require professional help very soon.
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