A monthly start over the winter keeps a marine generator from sitting completely dead, and it is better than doing nothing. It is not a layup. Five minutes unloaded does not circulate antifreeze through the raw-water side, does not replace oxidized fuel, and does not tell you the impeller took a set in November. The unit that “ran fine in January” is still the one that fails the first hot weekend in April.
That April pattern is the one we already documented in why marine generators fail in the first month of the season. This post is the work that belongs on the other side of that sit: what a Kohler, Onan, Westerbeke, or similar marine genset needs before the boat is laid up, not after it has been sitting for five months.
Why a monthly start is the wrong kind of run
Starting a generator and letting it idle with no load is easy on the calendar and hard on the engine. Diesel engines like to reach operating temperature and carry a load. A short, cold, unloaded run leaves unburned fuel in the exhaust, moisture in the crankcase, and raw water sitting in the exchanger and mixing elbow. Then the unit sits until next month and you do it again.
If the boat is still in the water and you are going to run it, run it long enough to get hot, and put a real load on it: air conditioning, battery charger, the loads it will actually see in season. A five-minute start to “keep the oil moving” is theater. It is not marine generator service.
Once the boat is coming out, even a good loaded run is not the layup. The cooling system still has water in it. The fuel still sits. The impeller still takes a set in a pump that will not turn until April.
Fuel is the first thing that goes stale
Most marine generators share a tank with the main engines. The generator pickup is often in a slightly different part of that tank, which means it is the first thing to drink the water and sediment that settle over winter. A monthly start pulls a sip of that fuel, clogs the primary a little more, and then the unit sits again.
Before layup, treat the fuel, change the generator’s primary and secondary filters, and drain the bowl so you are not storing a filter full of water. If the tank is half empty, top it. The generator does not get a pass because “we will run the mains more.” It is on the same fuel.
Cooling and the impeller that nobody thinks about
A marine generator has the same two-circuit cooling layout as the propulsion engine on most of these boats. Raw water still has to be drained or displaced with nontoxic antifreeze. Closed coolant still has to be at a freeze rating that will survive a Waretown January. The exhaust elbow still holds water if you leave it.
The impeller is the part that gets skipped because the generator is not the engine people think about at haul-out. Rubber vanes take a set when they sit pressed against the cam in a dry or half-wet pump. In April they tear, the genset overheats on the first loaded run, and now you are buying an impeller and maybe an exchanger. Pull it or replace it at layup. Leaving it “because it still pumped in October” is how spring generator calls start.
Oil, batteries, and the engine room
Change the oil and filter so used oil is not sitting on the insides until spring. The published interval on our generator work is every 100 to 200 operating hours, or at least once a year, whichever comes first. Layup is the yearly shot for a lot of recreational boats that only ran the genset on hot weekends.
The start battery is its own problem. A generator that has not been on a maintainer will ask a cold, sulfated battery to crank a diesel in April. Charge it, keep it on a maintainer, or take it home. Check the terminals. Salt air in a closed engine room all winter is rough on the control board and the harness, which is why a look at the wiring belongs on the same visit as the fluids.
We are factory authorized on Kohler and Onan, and we service Westerbeke and the other marine sets that show up in Jersey engine rooms. The layup steps do not change much by badge. The access does, and so does whether anyone has opened the unit since last spring.
Do the layup once, then leave it
If the boat is on the hard, the generator should be winterized and left. Monthly visits to bump-start a dry, antifreeze-filled raw-water pump are a good way to run the impeller without water. If the boat stays in, a loaded run to temperature is useful. A ritual start is not.
Call Forked River Diesel at (609) 242-8448 if the generator did not get a real service this season and you want it laid up with the mains. Finding the fuel, cooling, and impeller problems in October is quieter than finding them the first weekend you need air conditioning.
Have any questions? Contact Forked River Diesel and Generator for support with your marine diesel engine or generator concerns.