The week before the boat comes out of the water is when the engine work that still needs running water has to happen. Once the boat is on the hard you can still change oil and service the closed cooling system. You cannot run the raw-water pump against a real intake, check the exhaust under load, or confirm the engine actually reaches temperature with water flowing. Do those checks while the boat is wet. Save the drain-and-fill work for after it is blocked.
This is not a full winterization checklist. We already published a broader winterizing guide. This is the short list of diesel items that get worse, or become impossible, after the boat leaves the water.
Run it like you mean it, once
Take the boat out, or at least run it at the dock against a hose if that is how the engine is cooled at rest, and get it to operating temperature under load. Watch the temperature gauge the way you would in July. A slow climb that never showed at idle will show at cruise. Listen for the raw-water pump. Confirm a solid stream at the exhaust. If the engine is already running warmer than it did in June, that is information you want now, while you can still pull a strainer or inspect an impeller, not in April.
That run is also the last chance to see how the engine actually behaves before five months of sitting. Hard starting, smoke, or a hunting idle belong on this week’s list, not on a spring surprise list.
Raw water, strainer, and the impeller
Open the sea strainer and look at what a season of Barnegat Bay left in it. Grass, silt, and the odd jellyfish debris are normal. A strainer that has been ignored will pack tight enough to starve the pump. Clean it. Exercise the seacock so it still turns. A seacock that froze in place over the summer is easier to free now than after it has sat dry all winter.
If the impeller has not been pulled this season, pull it before haul-out or plan to replace it as part of the layup. A set impeller is a spring overheat. The raw-water circuit inspection we do in April is the same circuit. Doing the obvious failures in October means April is a check, not a rescue.
Zincs, bonding, and stray current
Sacrificial anodes on the shaft, rudder, trim tabs, and inside the heat exchanger only work while they are in the water and still have metal left. Check them before the boat comes out. A zinc that is gone in October tells you what the season did. Replacing it next spring does not undo the metal that was next in line all summer.
If the zincs are disappearing faster than they used to, that is usually stray current, not “bad zincs.” A bonding wire that has come off a strut, a shore-power fault on a dock pedestal, or a neighboring boat leaking current into the water will eat anodes in weeks. Look at the bonding jumpers on the engine, the exchanger, and the underwater metals. A green, powdery connection is not bonding anything.
Internal zincs in the heat exchanger are easy to forget because they are not visible from the dock. If nobody has pulled those plugs this year, this is the week to put it on the shop list. Once the boat is on the hard the external anodes are easy. The internal ones still take an engine-room visit.
Fuel, oil, and what can wait until the boat is blocked
Top the fuel tank before the boat sits. A half-empty tank through a Jersey winter is the condensation problem. Add biocide if that is part of how you store diesel. You can change oil and fuel filters on the hard, and many owners prefer it that way because access is better and there is no hurry. If the oil is already black and the last change was a long time ago, changing it while the engine is still hot from that last run is better than changing cold oil a week later, but it is not the item that has to happen in the water.
Batteries can wait a day. Getting a full charge into them before they sit cannot. If the charging system has been weak, that last run will not save a sulfated bank. Test it now, while the engine can still spin an alternator.
Make a list for the shop, not a pile of surprises
Write down hours, anything the gauge did, zinc condition, and whether the generator ran. Hand that to whoever is doing the engine work. Maintenance at layup goes faster when the week-before notes are real. Forked River Diesel is at Holiday Harbor Marina in Waretown, and October is when this list hits every diesel in the yard at once. Call (609) 242-8448 before the boat is already on the hard if the raw-water side, zincs, or a loaded test run still need doing.
Have any questions? Contact Forked River Diesel and Generator for support with your marine diesel engine or generator concerns.