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.

Seeing Is Believing

A Close Look Might Reveal Trouble Beneath The Surface

Photo of Old and new pop-off valve from a water heater
Old and new pop-off valve from a water heater. Notice the green area of the old valve, an indication of leaking.

A periodic visual inspection of important components could prevent a bad surprise later, if you know what to look for. Areas of rust, or a small crack or scaling on a stainless-steel component, may be a sign of crevice corrosion, which could result in failure of the part.

  • Gelcoat cracks may be of only cosmetic significance, but they could indicate serious flex from too much stress in the area, or delamination underneath.
  • Changing exhaust color with no obvious cause may be a precursor to problems. Generally, black exhaust means fuel burning poorly; white or bluish smoke may indicate excessive oil burning; and steam can indicate overheating. But exhaust colors have many nuances. Diesels emitting black smoke could need a new air filter. Diesels billowing smoke might need new injectors. Gas engines might smoke on startup, but more than 10 seconds could indicate a problem with the fuel mixture. Steam from either engine type could mean water getting past the head gasket (and will be accompanied by the smell of steamy water or antifreeze).
  • Frayed lines may be evidence of age and too much exposure to UV, chafing, and poor fairleads. Figure out the cause and address it, and then replace the line.
  • Photo of cracking, rusted and pitted of the shaft
    Observing closely in areas where problems are likely to occur may alert you to potential issues. Cracking, rust, and pitting of the shaft, visible here at the stuffing box, are an indication that the shaft should be pulled, inspected, and likely replaced.

  • Discoloration of metal parts in contact with water could indicate corrosion or electrolysis. Unusual discoloration of heated metal parts can indicate excessive heating. Many metal parts (such as an exhaust manifold) subject to high heat will discolor to some extent, but watch for continued, more noticeable discoloration of these parts. Discolored paint can also indicate excessive heat. Bronze parts that have turned pink may indicate a stray current problem.
  • Discoloration of wire terminals or insulation could be a sign of excessive heating or corrosion underneath the insulation.
  • Photo of cutlass bearing
    Shaft wobble in the worn cutlass bearing produces excessive vibration, compared to the new cutlass bearing.

  • A sheen on the water at your exhaust when the engine is running can indicate poor burning of the fuel. Possible causes could include bad injectors, timing, plugs, or poor compression, as from valve or ring problems. Pull the spark plugs on your gas-powered engine. Beige or brown is the right color. Grey indicates detonation/timing issues. The sheen could also indicate lube oil entering the exhaust or transmission oil escaping into the exhaust through a leaking heat exchanger.End of story marker

Award-winning writer and long-term liveaboard, Tom Neale is a BoatUS Magazine contributing editor and key member of our "Ask The Experts" tech team.

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