Winterizing Your Ski Boat

Winterizing Your Classic Inboard Ski Boat

By Ron Tanis

This guide will work for most DIRECT Drive ski boats, and how it’s done in our shop..

1) FUEL SYSTEM –  Ideally on the last day of using your boat you will have added an appropriate amount of fuel stabilizer to your fuel tank, allowing the stabilizer to mix and enter the entire fuel system. (Most of us forget to do this) If you forgot to do this, then you will need to add it now, then run the engine “on the bucket”.

EFI engines run for 5 min. minimum

Carb engines run for 20-30 min.

(optional) This is also the time to “FOG” your engine, a process where you add fogging oil (I use 2-cycle oil) into the throat of the carb., or throttle body while running just before you shut the engine down for the season. About a pint will do, just pour a steady stream of oil into the engine, if it runs too rough, slow down the pour. This coats the upper engine parts with an oil film for protection. Note: the exhaust will be smoky, and will be smoky when the engine is re-started in the spring.

2) Water Draining – I recommend using a zip-lock bag to keep all plugs in then place on top of the engine when done.

Exhaust Manifolds, remove drain plugs – or- open drain plugs if equipped to drain exhaust. If nothing comes out, suspect blockage & clear, you should get a pint or so from each exh. manifold. Many engines will have a 3/4″ plug at the rear of the manifold requiring a 1/2″ drive ratchet to insert & remove, some may have a center drain, and others may have a drain valve. 

Engine Block, each side of the engine block has a drain plug, or small valve. Remove, or open the drain valve, and again about a quart of water should rush out, if not, the opening is blocked & needs to be cleared. It is not uncommon to find rust & scale blocking the opening, nor is it uncommon to find worn out drains or petcocks, replace as needed. EFI NOTE:  the engine block drain on the starboard side will have a “Knock Sensor” threaded into the drain, this needs to be removed (unless equipped with a Tee & drain petcock) pinch the single wire connector & pull off, then using a socket remove the sensor being careful not to drop the sensor, there is a crystal inside that is sensitive.

SPECIAL NOTE: These engines were designed for level automotive installations, our boats have 12+ degrees of incline and presents a unique block draining problem. After opening the block drains ALWAYS lower the front of the trailer down as low as possible to help “level” the engine and drain the back of the block. FORDS are especially prone to this as the Ford drains are offset with the Starboard drain near the front of the engine, trapping most of the water behind the drain.  

Engine Front, Ford & Gm will all have a large  “J” hose connecting the water circulation pump and the upper water manifold, Remove the lower “J” hose connection from the circulation pump, drain & leave off for winter. Raw water pump, remove hoses & let drain, leave off for winter. On crank driven pumps where it is easy to remove the front cover to remove the impeller I would remove the impeller & bag it.

Trans Cooler, depending on location you may need to remove the water hose from one end IF it is located where it will trap water, some coolers are mounted vertical and dropping the hose from the raw water pump will accomplish the same thing.

SeaWater Strainer, if yours is mounted “clear bowl” up, do nothing, if the clear bowl is mounted down & holding water, remove and bag it.

3) Other Items:

Loosen belts

Remove hull drain plugs & bag

Disconnect battery

Lift all cushions & allow to dry before covering up

Boats with Computer driven instruments need to disconnect or drain the (2) pitot tubes going into the MDC controller

Spray engine & engine mount threads with some WD-40

Block up the motor box with a small piece of 2 x 4 to allow air circulation

Boats equipped with heaters need to find and disconnect the hoses at the engine, drain, then blow on one hose to force any water out the other, then leave laying in the bilge.

Boats equipped with hot water showers need to drain the lowest hoses

Boats with the original Airguide Contralog speedometers should pull the hoses off the back of the speedo’s and blow back, this will prevent the ballast tubes from freeze damage.

Remember a clean dry boat survives a cold winter better than a wet & dirty one!

Anti-Freeze: This is really for the pro’s to do as an extra level of protection, to do this right either the engine needs to be run up to operating  temp, while circulating on an anti-freeze solution, -or- the engine needs to be drained, then plugs put back in, and antifreeze added into the block by-passing the thermostat.

Oil Change: Some change when winterizing, others recommend doing this during the spring start-up. Most shops prefer in the fall as they are not as rushed as in the spring, engine manufactures vary in recommendation. I prefer to do this in the spring start-up for the following reason. Most ski boats have very little hours on the oil to begin with, but under many circumstances while stored you may accumulate condensation in the engine, if you store the engine with new oil, accumulate water then start up in the spring you will have water in the oil to burn off which takes longer in a 160 deg. engine than a 198 deg. car or truck. I prefer to store the engine with the “used oil” then drain the used oil and any accumulation of water in the spring, add new oil & filter & there is no water to burn off.   

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