Knocking in Engine Compartment
Sounds like: A woodpecker chopping away on a hollow log, but in this case, itís your gas engine.
Cause: Probably a loose connecting rod. Old age will cause it to loosen, but so can a lack of oil, low oil pressure or excessive stress on the engine.
Metallic Tapping in the Engine Room
Sounds like: A vaudeville tap dancer two-stepping on your gasoline engine.
Sounds like: A high-pitched whir that gets louder with an increase in rpm.
Cause: Itís normal to hear this sound. Usually itís just the alternator charging the battery after the boat hasnít been used for a while. An alternator with high amperage output will be even louder. The noise will continue if you constantly use power.
Remedy: Youíll have to be patient and allow the batteries to recharge. With batteries property maintained and not completely drained, you may avoid this noise in the future.
Flapping While Gas Engine is Idling
Sounds like: An army of crickets taking over the engine room.
Cause: Some stern-drive engines have flapper valves inside the Y-pipe to prevent water from entering the engine through the exhaust. When the valve is worn, the exhaust beats the valve against the pipe, producing a metallic sound.
Remedy: Youíll be able to get home, but when you do, remove the exhaust bellows to gain access to the valve and replace it with a new one. (The boat will have to be hauled out first.) It will take about an hour and cost almost $200. Itís a good idea to check the valve yearly. At the same time, look for exhaust leaks and tighten hose clamps that have loosened.
Pinging from a Gas Engine
Sounds like: Chirping birds in the engine compartment. Usually heard
when running under severe load.
Cause: Probably poor-grade or low-octane fuel. Itís known as engine ping or detonation. Basically, the uncontrolled burning of the fuel/air mixture produces it.
Remedy: Pull back on the power slightly until the ping disappears. Get
to a marina and buy higher octane. If they donít sell fuel, buy a can of octane booster. (Donít use both.) If you allow this condition to continue, it can lead to engine damage. Severe detonation happens even before you hear the ping.
Clanking as Boat Planes
Sounds like: A bag full of aluminum cans rattling on the hull. Also heard when the boat slows down.
Cause: It may be a broken baffle in the fuel tank. When the boat stops or accelerates, fuel sloshes fore and aft, rattling the aluminum baffles.
Remedy: Tanks arenít cheap to fix, so hope itís not the baffle. Maybe itís just a few empty soda cans rolling around the bilge. If itís the baffle, see a mechanic when you get back to the dock.
High-Pitched Screeching Gas Engine
Sounds like: A squealing pig. Especially shrill when boat hits high rpm.
Cause: Slipping fan belts. They tend to burn and squeal loudly when worn or coming loose.
Remedy: Youíre probably foresighted enough to carry a spare emergency V-belt onboard, but if the belt breaks and you donít have an extra, tie anything that can be tightened around the pulleyóit may get you safely back to shore. In the future, inspect V-belts and tighten often; they tend to stretch out.
Squeal from the Cockpit
Sounds like: Fingernails scraping against a blackboard.
Cause: If you hear this sound as you slow your inboard-powered boat down to an idle, it means coarse sand has gotten into the cutlass shaft bearing. If you hear the noise while traveling at low rpm, itís probably a new cutlass bearing breaking itself in.
Remedy: Bearings are self cleaning so the noise should dissipate over time. The noise from a new bearing will also subside with regular use.
Hollow Sound from Exhaust Port of Inboard Engine
Sounds like: The engine is running without a muffler.
Cause: Bad water-pump impeller.
Remedy: Check the raw-water flow and watch the temperature gauge.
Overheating may follow so slow down, run on one engine or change the impeller. To double check, place hand on water pump faceplate. If itís hot, youíve cooked the impeller and need a new one.
Squeal from Front of Engine
Sounds like: Grating metal.
Cause: A bad water pump bearing is the likely culprit.
Remedy: The pump will need to be rebuilt, so travel slowly back to the dock to avoid rendering the pump useless. Keep an eye on tempurature.
Loud Chattering from Diesel Engine
Sounds like: Metal plates knocking against each other.
Cause: Poor quality fuel with low cetane rating, air in the fuel system or a bad injector nozzle.
Remedy: Cetane boosters added to the fuel will up the ignition quality; air in the system must be carefully tracked down (start at the filters).
Injector problems usually require the services of a mechanic, but most of them can be traced to bad fuel or water in fuel that gets past the filter system.
Clicking from Electrical Breaker
Sounds like: A pen click when you hit the head button, followed by silence if itís malfunctioning.
Cause: The motor is seized, usually from lack of use or sitting idle during the week.
Remedy: Unscrew the faceplate of the motor and, using a pry bar, twist the motor to unseat it. Hit the buttonóitíll work.
Low Clicking from bilge pump? Replace it, itís on the road to seizing when you need it.
Popping Noise Over the VHF
Sounds like: A muffled firecracker. Usually increases tempo when you
shut off the engine.
Cause: Itís the ignition. Each pop is a spark plug firing.
Remedy: Install a suppressor resistor in the high-voltage wire between the coil and the distributor cap.
Smell of Fuel, Propane Diesel or Gas
Smells like : Well, Fuel, Propane Diesel or Gas
Cause: It's the fuel system that is leaking.
Remedy : Shut down immediately (use the engine shutoff); if you don't suspect fire, open up everything. Odors of gas, diesel, or propane down below or on deck require immediate attention. Tanks should show no evidence of leaks, nor should hoses be mushy or soft.
Smell of Sewage
Smells like : Sewage
Causes: A dirty bilge