How to Winterize a Diesel Marine Engine

Written by will charpentier
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Before that first icy blast of a north wind streaks through your bones, making you wonder why summer had to end, your boat and her diesel engine will be ready for winter. Making a diesel motor ready for winter lay-up--winterisation--includes most of the normal maintenance tasks, done one more time, and will follow the season. Extra tasks involving the raw-water, mechanical and fuel systems are added to the checklist to complete the process.

Skill level:
Moderately Challenging

Things you need

  • Diesel fuel biocide
  • Motor Oil
  • Oil filter elements
  • Air filter covers ("socks")
  • Air filter element
  • Secondary fuel filter elements w/gaskets
  • Primary fuel filter elements
  • Garden hose
  • Propylene glycol
  • Grease gun
  • Heavy marine grease
  • Stuffing box rope
  • Pipe wrench
  • Red tags
  • Safety glasses

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  1. 1

    Fuel the vessel to capacity and add a biocide to the fuel tank. Change the oil and replace the oil filter. Change the air filter "socks" or the filter element.

  2. 2

    Remove the clear plastic domes from the secondary fuel filters, remove the elements, replace the filters and gaskets, and replace the dome. Do not fill the dome with fuel. Unscrew the cap of the primary filter, replace the element and screw the cap back onto the filter.

  3. 3

    Disconnect the raw-water pump's outlet hose. Disconnect the discharge hose for cooling water where it connects to the exhaust manifold. Use a garden hose to run fresh water into the hoses to rinse deposits from the system.

  4. 4

    Reconnect the raw-water pump's outlet hose. Use a funnel to pour a mix of half propylene glycol and half fresh water into the cooling water discharge hose until the hose and block are full.

  5. 5

    Reconnect the cooling-water discharge hose to the exhaust manifold and allow the antifreeze mixture to stay in the engine block for ten minutes. Open the drain plugs for the raw-water system and allow the engine block to drain.

  6. 6

    Lubricate the throttle linkage zerk fittings with a grease gun and heavy marine grease. Repack the stuffing box if necessary and, with the grease gun, grease the stuffing box.

  7. 7

    Whether the vessel will be stored ashore or in the water, tighten the bolts on the stuffing box with a pipe wrench until the normal dripping ceases. Tie a red tag to the propeller shaft where it enters the stuffing box and tag the throttles to remind you that the stuffing box needs adjustment before the vessel is used.

Tips and warnings

  • If your vessel is equipped with air throttles or an air start system, bleed the system down and allow the compressor to build the air pressure back up before shutting down all electrical services aboard. A tank under pressure will bleed somewhat unless refilled by the compressor, but if the weather isn't consistently cold and dry. an empty accumulator tank will pick up more water from condensation than a tank under partial pressure.
  • Wear safety glasses throughout the process of winterising a diesel motor or performing any other maintenance aboard.

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