How to Winterize a Marine Generator (and Recommission It in Spring)

Start the generator with its seacock open and run it until it reaches normal temperature, ideally with some load on it (Westerbeke's monthly exercise routine runs it at 70 to 85% of its rating for an hour, then a short no-load cool-down). Northern Lights says to reach at least 140°F. Warm oil drains better. Listen for odd noises and look for leaks while it runs.

Makers differ here, so check your manual:

• Northern Lights says to run the engine from a small, clean fuel source dosed with a diesel fuel stabilizer or conditioner (it names specific brands in its tips) so treated fuel fills the injection system.
• Westerbeke says to top off the tanks and add additives to control algae and condition the fuel, making sure they're compatible with your filter/separator.
• Gasoline generators need a marine stabilizer run through the carburetor or fuel system; see the ethanol fuel care guide.

The fuel additives guide explains biocides, stabilizers and conditioners. On most boats the generator shares the main fuel tank, so treat the tank once for both.

Northern Lights and Westerbeke both say to change the oil and filter before storage. Westerbeke explains that used oil and combustion deposits form harmful chemicals that shorten the life of internal parts during a lay-up. Pump or drain the warm oil, fit a new filter (a film of oil on its gasket), refill with the oil your manual lists, run briefly and check for leaks.

Drain any water from the separator bowl and change the filter elements if due. Bleed the fuel system as your manual shows, then run the generator a few minutes so treated fuel fills the filters and lines. Westerbeke says to check every fitting you touched for leaks.

Most marine generators have a closed coolant circuit with a heat exchanger. Test the coolant's freeze protection. Westerbeke recommends a 50/50 mix year round (stronger in very cold areas). Northern Lights' storage list says to drain, flush and refill with a premixed 50/50 heavy-duty diesel engine coolant. Use only the coolant type your manual names in this closed side; pink RV antifreeze is for the raw-water side only. See the closed cooling guide.

Shut the generator off and close its raw-water seacock. Open the raw-water strainer, clean the basket and check the lid seal. Strainers left full of water can freeze and crack. Check the heat exchanger zinc too if your set has one.

With the seacock closed, take the intake hose off the seacock (or the strainer outlet, per your layout) and put it in a bucket of fresh water. Start the generator, let it pull the bucket through, and shut down before the bucket runs dry.

Refill the bucket with propylene glycol antifreeze mixed as the label says for your winter low; Westerbeke suggests mixing it slightly stronger than needed. Westerbeke says either propylene or ethylene glycol works in the raw-water side, but many owners use the pink RV type because it's less harmful, and none of it should go overboard. Start the generator and let it draw the mix until it comes out the exhaust colored, then stop before the bucket empties. Catch what comes out of the exhaust. A generator needs far less antifreeze than a main engine, but long exhaust runs and water-lift mufflers add up, so have extra. Reconnect the intake hose.

Westerbeke's lay-up routine says to take the impeller out of the raw-water pump (catch the antifreeze that comes with it), inspect it, buy a replacement and a cover gasket if needed, and leave it out until spring. Vanes left bent all winter take a set. Tape a note on the pump and the start switch: "IMPELLER OUT."

Northern Lights' storage list includes loosening the alternator belt so it doesn't take a set or stress the bearings. Mark the belt tension or take a photo so you can set it back in spring. Check its condition and buy a spare if it's cracked or glazed.

Northern Lights says to seal the intake and exhaust openings with heavy plastic bags closed at the bottom, with a few desiccant packs inside to soak up moisture. Westerbeke describes a lightly oiled cloth in the intake opening and exhaust thru-hull, and warns never to push it out of sight. Yachting adds that sealing the openings also keeps out wasps and mice, which love an exhaust outlet. Tag every plugged opening on your "remove before start" list.

Sound shield: Fischer Panda's winter storage list says to leave its generator enclosure slightly open (one latch undone) so air can circulate and moisture doesn't stay trapped inside. Check what your maker says for its sound shield.

Charge the generator's start battery fully. Westerbeke says batteries left aboard must stay fully charged so they can't freeze; otherwise remove them. Westerbeke also says D-Net (digital) generators should have their DC breaker and NMEA 2000 power turned off for long storage so they don't drain the battery. Turn off the generator's DC breaker or battery switch.

BoatUS suggests using lay-up time to pull the sound shield panels and check for loose or corroded wiring, chafed hoses, cracked exhaust hose and clamps, and blocked ventilation. Order filters, impeller, belt and zinc now. Write down the date, hours, fluids used and every removed or plugged item.

Onan owners: Cummins' storage list for its Onan marine sets adds a few items worth copying on any brand: run the set under as much load as you can (up to its rating) before lay-up and note how it behaved, test the control and safety shutdowns where you safely can, replace coolant that's two years old or more, drain and clean the raw-water side of the heat exchanger (heavy scale may need a dealer), and lightly oil any parts that tend to rust. In spring, it says to clean or replace corroded terminals and, on sets that have them, clean and inspect the generator's brushes and slip rings before the first start. Write down any fault you noticed in the fall so it gets fixed before the season.

• Open your "remove before start" list: take out the intake and exhaust bags or rags, refit and tension the belt, install the impeller (lube it only with what the pump maker allows) and a new cover gasket.
• Check oil and coolant levels, reconnect and charge the battery, and inspect hoses and clamps.
• Open the raw-water seacock. Northern Lights' tips say to start with the AC load breaker off (and the shore power breaker off if you're at the dock), warm up for a minute, then connect the load. Confirm water flows from the exhaust within seconds, as the USCG CO checklist also asks. If it doesn't, shut down at once and find the cause.
• If it won't start after you changed the fuel filters, Northern Lights warns not to crank more than about 60 seconds in total: the raw-water pump keeps filling the muffler and can flood the engine with seawater. Re-prime the fuel system instead (and drain the muffler if needed).
• Run it until warm, then put a load on it and check voltage and frequency (BoatUS says US generators should hold their rated voltage and 60 Hz under load). Watch for leaks and the antifreeze being flushed out.
• Test your CO alarms before overnight use (USCG checklist).