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Boat Winterizing

In our last article, we were flushing the boats cooling system, draining all water by trimming the propeller to the full-down, running position. Additionally,

  • Newer sterndrives and inboards have several drain plugs in the exhaust manifold, power steering cooler, oil cooler and/or fuel canister. Consult your manual.
  • Older sterndrives and inboards typically have brass drains in the lower crankcase and bottom of the exhaust manifolds.

The raw-water cooling circuit is flushed with a freshwater connector or by closing the intake seacock and disconnecting the hose on the outlet side of the pump, as well as the exhaust manifold. Run fresh water into the hose to back-flush.

Use your service manual to guide you in preventing corrosion and freezing in an engine block or heat exchanger:

  • Reconnect the water-pump outlet hose.
  • Pour a 50/50 mix of propylene glycol antifreeze into the disconnected discharge hose until full.
  • Leave the mixture inside the block for several minutes.
  • Open all drain plugs and drain the engine.

Remove the pump’s impeller, rinse it, grease it and reinstall it, or wait until spring.

Engine oil, drive gear lube, and transmission fluid should be drained and refilled to flush out water and contaminants. Run the engine to promote flow and change the oil filter and fuel filter.

Some feel fuel stabilizer treatment is enough, others will want to coat the engine’s interior with oil for further protection. Fogging is done after running the storage lubricant through the fuel mixture, protecting bearings, seals, and rotating surfaces from rust and corrosion.

  • Engine running: squirt the oil into the carburetors/fuel-injection system air intakes until it begins to smoke heavily and stalls.
  • Engine shut down: remove the spark plugs and spray the oil into each cylinder. Rotate the flywheel manually, pull the kill-switch lanyard, and adjust the key switch to turn the engine over without starting.

Winterization can keep boaters in tune with their engines and systems!



Tiger, J., 2013. Top Winterizing Tips, https://www.boatingmag.com/top-winterizing-tips

Image Credit: Ebay.com, How to Winterize Your Boat