Marine Generator Routine Maintenance and CO Safety

Press the test button on every CO alarm aboard. They should be marine-rated (look for UL 2034 marine listing) and within their "replace by" date; replace them as the maker recommends. Know where the generator exhaust outlet is. If it is near the swim platform, make a rule aboard: generator off whenever anyone is on the platform or in the water.

Turn the generator off at its panel, switch the AC selector away from "generator," and switch off the generator's start battery or remove its control fuse if your manual says so, so nobody can start it remotely. Let it cool. Close the generator's raw-water seacock.

Remove the inspection panels or the whole shield. With a flashlight, look for: oil or fuel drips, coolant crust, salt deposits, rust or black streaks around the exhaust parts, loose or cracked hoses, chafed or loose wires (especially where they pass through the shield), a frayed belt, and debris in the cooling air openings. BoatUS recommends doing this regularly because the shield hides problems.

Warm the generator for a few minutes first if your manual allows, then shut it off. Pump out the oil through the dipstick tube or drain hose, change the filter (rub clean oil on the new gasket, hand-tight plus the amount on the filter), and refill to the full mark with the oil your manual specifies. Recheck after the first run. Milky oil means water or coolant inside: call a pro.

With the seacock closed, open the strainer, empty the basket, rinse it and check the lid gasket. A generator strainer is easy to forget because it is separate from the main engine's.

Remove the pump cover and inspect the impeller for cracked, stiff or missing vanes. Many owners replace it every year or at the hours in the manual, whichever comes first. Find any missing vane pieces in the heat exchanger inlet. Use a new gasket, lubricate as the impeller maker recommends, and see our raw-water impeller guide for the full method. On some generators the pump is hard to reach; if you have to remove other parts, follow the manual.

Drain any water from the separator or filter bowl into a clear container. Replace the fuel filter at the interval in the manual, with new O-rings. Many modern generators have an electric fuel pump and will purge air when you hold the prime or preheat switch; older ones may need manual bleeding. Use only the method in your manual and wipe up spilled fuel.

Inspect the air filter or intake silencer and clean or replace it as the manual says. A clogged intake makes black smoke and wastes fuel.

Generator exhaust leaks are a common CO source. Look along the whole exhaust path:

• Exhaust hoses: cracks, soft spots, charring or bulges mean replace.
• Clamps: rusty or loose clamps; many installers double-clamp exhaust hose connections.
• Mixing elbow and water-lift muffler: rust, black soot streaks or salt crust around joints are signs of leaks.
• Vented loop or anti-siphon valve (if fitted): it must be clean and working, or seawater can siphon into the engine.

Anything leaking, cracked or heat-damaged is a stop-and-call-a-pro item. Northern Lights recommends a close look at the wet exhaust elbow at least once a year and replacing it at the first rust spots, leaks or cracks. A handy running check: if you see steam at the exhaust or higher-than-normal temperatures, carefully feel the muffler and its hoses. Hot to the touch means raw-water flow is restricted (strainer, impeller, pump belt, heat exchanger or a carboned-up elbow).

Some generators have zinc anodes in the heat exchanger (others, such as smaller Northern Lights units, have none); replace them when about half gone (typical; confirm in your manual). Until you know how fast yours wear, Northern Lights suggests looking at them every 90 days. On closed-cooled (freshwater) units, check the coolant level in the recovery tank with the engine cold. Never open a hot pressure cap.

Most generators have a dedicated start battery. Clean and tighten its terminals, check its charge, and make sure it is being charged by the generator and the battery charger. A weak battery leads to long cranking, which on a wet exhaust can flood the muffler and engine.

Open the raw-water seacock. Restore power to the controls. If you are at the dock, turn off the shore power breaker first: Northern Lights warns that a worn shore/generator selector switch can connect the generator to shore power, with expensive results. Make sure the generator's AC output breaker is off. Start the generator from its panel and immediately confirm cooling water is coming out with the exhaust. If not, shut it down within a few seconds and find out why. Look for leaks at everything you touched.

If the generator starts but dies the moment you let go of the start or preheat switch, Westerbeke suggests holding the switch a few seconds longer after it fires so oil pressure can build. If it still shuts down, a safety switch has probably tripped (low oil pressure, high coolant temperature, or high exhaust temperature from poor raw-water flow). Don't keep restarting it: check oil and cooling water, then call a technician.

Let it warm up for about a minute before you switch on the AC breaker, then turn on a moderate to heavy load (water heater, air conditioning). When you shut down, reverse it: AC breaker off, let it run unloaded for a minute or so, then stop it. Northern Lights says this habit protects the voltage regulator and generator diodes. The generator should hold steady under load. Check the AC volt meter on the panel, or have a pro or knowledgeable owner check voltage and frequency. In the US the output should be close to 120 or 240 volts at 60 Hz. BoatUS suggests that a voltage difference of more than about 5 to 6% between no load and load is worth investigating. Do not adjust the governor or regulator yourself unless your manual covers it and you are qualified.

A generator that sits idle for months suffers: seals dry out, fuel goes stale and moisture collects. Many makers recommend running it under a real load for about 30 to 60 minutes at least once a month (typical; confirm in your manual). Westerbeke spells out a monthly routine for its diesel generators: do the daily checks, warm it up (usually 5 to 10 minutes), run it for about an hour at roughly 70 to 85% of its rated output, then let it run 5 to 10 minutes with little or no load to cool down before shutting off. The cool-down matters most on turbocharged units. Long periods at very light load can cause unburned fuel buildup in diesel units ("wet stacking"), so give it a meaningful load. Northern Lights suggests keeping its generators at roughly 40 to 50% of rated load or more, and running small loads from the inverter instead; light loading plugs the exhaust elbow with carbon. For units that don't run many hours, its rule of thumb is oil and filter twice a year (spring and fall), fuel filter and air filter once a year, and a new raw-water impeller every year before the season. Record hours, service done and parts used in BoatMend.