Winterizing Your Engine

November 7, 2017


As temperatures fall, water will freeze, we know that… but when that water is inside an engine or gearcase, a cracked block or housing might be the net result, along with astronomical repair bills !

You can prevent this, and sleep well on those cold winter nights by taking the right steps now….

Remember that Neglect = Trouble next season !

Make a Check List - It’s important that you don’t miss anything, so a detailed list is a good place to start. Review your owner’s manual for winterizing instructions specific to your engine or follow these generic instructions:

First, get some supplies…. A spray can of engine fogging oil*, a few gallons of “pink stuff” (propylene glycol antifreeze – non toxic) the appropriate engine oil and filter, transmission fluid, some engine antifreeze and some fuel stabilizer or diesel fuel biocide.  *Fuel injected (EPI / MPI) engines will require a winterizing mix of fuel, oil and stabilizer.

Second, roll up your sleeves…..

Coolant   For inboards and stern drives with a closed loop cooling system with heat exchanger, check, top off or replace your engine coolant with a 50/ 50 mix of new antifreeze. Run the engine to distribute the mix throughout the system.

Oil & Gearcase Fluid Change  Run your engine until it reaches temperature, then change the oil and filter. (Pumping cold oil leaves residue, acids and deposits)

Fill your fuel tank to about 90%. This leaves room for expansion in the Spring when it get’s warmer.  Filling the tank prevents condensation from forming and water from accumulating. Alternatively empty the tank - if feasible.   Add biocide to diesel fuel to kill potential growth of bacteria.  For gas, add stabilizer. Whether gas or diesel, run the boat to mix it up. Dumping it in when the boat is laid up won’t allow it to distribute through the fuel system. Even if you use premium ValvTect fuel, adding some additional ValvTect stabilizer for the Winter is a good idea.

Flush the Salt Water cooling system (inboards) -  take off the hose to your intake thru-hull or the sea strainer and stick it into a bucket.  Run a hose (with a shut off valve on the end) into the bucket and run the engine, ensuring you don’t run it dry. This may mean starting and stopping to allow the hose to fill the bucket.  This will circulate fresh water through the system and rinse away salt residue. Next, open the engine drain plugs and drain the engine, taking care to root out any blockages that might prevent the block from draining. Once you have flushed and drained the engine, station someone where they can see the engine exhaust and pour the pink stuff into the bucket, starting and stopping the engine as necessary. When you have a steady stream of pink exhaust water, it’s done.  Don’t be tempted to dilute the pink – it will dilute itself with the fresh water already in the system….. this is not a place where you take chances to save some money !

Flush the Salt Water cooling system (outboards) -  attach your earmuff flushing tool and run the engine with fresh water. Then, using the short hose you have prepared (with a male hose fitting on one end), put a bucket of pink in the boat, prime and insert the hose. The engine water pump will suck the pink through the engine and out the exhaust and tell-tail “pee hole”. Don’t run dry !!  When a nice solid pink comes out - you’re done. At the same time you should disconnect the fuel line and be ready to spray fogging oil as the engine gasps and dies. (it’s much like cooking and having everything done and hot at the same time)

Carbureted Gas Engines – While running the pink through the engine, run the engine out of fuel and at it’s last stutter and gasp, spray the fogging agent into the air intake.   Removing spark plugs and spraying some fogging fluid is often recommended if you can get to the spark plugs. Replace the plugs now or in the Spring. For EPI / MPI engines, run the “winterizing mix” through the fuel system.

Raw water impellers – this is a good time to remove and replace the old impeller.

Spray the engine and components with a moisture displacing spray like CRC. Ask at the ships store for recommended products.  This stops rust and corrosion.  Remember corrosion & rust never sleep !

Outboards and IO’s – change your gear lube.  Drain and re-fill so moisture and acids don’t damage the gears and internal mechanism. Use new drain seals when changing the gear lube. Lube your prop shaft and change out the sacrificial anodes (zincs). Store IO’s and outboards in the down position.


Whew !     Congratulations, you are now ready to winterize all of the other systems on the boat !


By Captain Rick Delfosse  203-216-7800

Rick is a Coast Guard captain, National Safe Boating Council close-quarters boat-handling and open water boat handling instructor, Connecticut and New York certified safe boating instructor and a US Sailing-certified instructor.   He also conducts on-the-water courses and classroom seminars on coastal cruising and boating skills. The owner of a 43-foot pilothouse cutter and an Aquasport powerboat, he has extensive cruising and one-design, coastal and offshore racing experience.




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