4. Freeze Prevention
To avoid freeze damage and fight corrosion over winter, plumb the motor flushers or intake pumps to draw rust-inhibiting propylene-glycol antifreeze such as West Marine Pure Oceans minus 50 degrees F ($5.99/gallon, westmarine.com) from a bucket or tank, and run each engine until the solution exits the exhaust. Not only does this displace any standing water and coat the water jackets and heat exchanger with a corrosion inhibitor, but at the same time it distributes inside the engine and transmission a coat of the fresh, clean oil that you put in earlier to help prevent internal rust during storage.
Once the diesel is off, immediately shut down the supply of antifreeze to prevent siphoning liquid into the combustion chambers and hydro-locking the engine. Because antifreeze can swell some rubber materials, replace the intake-pump impellers next spring as part of your recommissioning process. If your boat has closed cooling, check the recommended maintenance schedule to see if you need to change the antifreeze in these systems as well. This is typically at 1,000 hours, but check the level regardless.
5. A Jump on Spring
While you can wait until spring, now is a good time to check zincs, belts and electrical connections, as well as the O-rings on fuel fills. Also inspect the physical connections at the transom and along the exhaust outlets — lots of water flows through here! Replace, repair and service anything that looks suspect or worn, and you’ll have that much less to do next spring.
6. All Sealed Up
Seal the exhaust outlets on the hull and air filters on the engine with heavy plastic and duct tape. This prevents moist air from finding its way into the combustion chambers via open exhaust or intake valves while your diesels are enjoying some well-deserved downtime.
Get more winterizing tips for marine diesel and gas engines at boatingmag.com/winterizing.