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Boat Winterization 101

CHRISTOPHER S. THURMAN, PH.D.

THURMAN MARINE SERVICES LLC

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Outline

Why Winterize?

Fresh Water Systems

Outboard Motors

Inboards/IO Sterndrives

Conclusions

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Why Winterize?

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Why Winterize? (1/4)

Prevent freezing water from causing catastrophic failure

Fresh water systems
Inboard motor risers/manifolds
Gearcase
General raw water cooled systems (generators, air conditioning, etc.)

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Fig. 2: Cracked Gearcase

SOURCE: https://www.thehulltruth.com/boating-boat-show-photos/80370-lower-unit-crack-superficial.html

SOURCE: https://www.thehulltruth.com/boating-forum/1323125-cracked-block-can-i-use-gm-car-block-replace-my-mercruiser-block.html

Fig. 1: Cracked Inboard Block

Before Freeze

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Why Winterize? (2/4)

Prevent corrosion/rust from standing water

Boat-/engine-side fuel system
Powerhead
General mechanical components/exposed metal (steering rods, tilt/trim rods, engine-side pivot points, prop shaft, etc.)

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Before Storage

Fig. 5: Corroded Tilt Ram

Fig. 4: Rusted Exhaust Valves

Fig. 3: Rusted Fuel/Water Separator

SOURCE: https://www.thehulltruth.com/boating-forum/939155-leaking-fuel-water-seperator.html

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Why Winterize? (3/4)

Fuel stabilization

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Before Storage

Fig. 6: Water-Contaminated Fuel Sample

Fig. 7: Water-/Rust-Contaminated Fuel Sample

Fig. 8: Contaminated Fuel during Polishing

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Why Winterize? (4/4)

Prevent battery damage

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Before Storage

Fig. 9: Charging Battery

SOURCE: https://www.thedrive.com/maintenance-repair/29835/how-to-charge-a-battery

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Why Winterize?

Prevent freezing water from causing catastrophic failure

Fresh water systems
Inboard motor risers/manifolds
Gearcase
General raw water cooled systems (generators, air conditioning, etc.)

Prevent corrosion/rust from standing water

Boat-/engine-side fuel system
Powerhead
General mechanical components/exposed metal (steering rods, tilt/trim rods, engine-side pivot points, prop shaft, etc.)

Fuel stabilization

Prevent battery damage

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Before Freeze

Before Storage

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Fresh Water Systems (1/1)

Run easily accessible faucet to drain all fresh water from system tank

Fill system tank with environmentally friendly antifreeze

Run all faucets, spigots, misters, etc. until pure antifreeze comes out

Pour antifreeze down fresh water drains if not done during Step 3

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Fig. 10: Generic Fresh Water System Diagram

Source: https://boatingmag.com/story/how-to/winterizing-a-boats-portable-water-system/?srsltid=AfmBOoqwOTcmA-c902gC9BCxybgUk5xbZG4703xtbAATeduY8l_dUbfn

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Outboard Motors (1/7)

Add fuel stabilizer to fuel tank(s)

Helps prevent fuel from breaking down (i.e., ‘going bad’)
Helps prevent water separation from ethanol

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SOURCE: https://www.boatus.com/expert-advice/expert-advice-archive/2013/february/forget-to-winterize-your-fuel

Fig. 11: Gasoline Fuel Stabilizer

Fig. 12: Diesel Fuel Stabilizer

SOURCE: https://www.wholesalemarine.com/sta-bil-diesel-fuel-stabilizer/?srsltid=AfmBOoq0us-gVMl5DUySSpa9qG69exSqkVZOq2l1dH1AKir6Xi2aSxDp

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Outboard Motors (2/7)

Check motor oil and gearcase oil for water intrusion. Always good practice to change both; however, only necessary if signs of water intrusion (i.e., milky oil).

Water intrusion in lubrication systems can cause internal corrosion
Water intrusion points toward other series issues that should be addressed before boat storage

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SOURCE: https://www.reddit.com/r/boating/comments/1ofr1ly/water_in_lower_unit/

SOURCE: https://www.boats.net/blog/milky-oil-in-outboard-common-causes?srsltid=AfmBOordKFNf16lOaC1S3eG-d_SoHHWlOUf0AQ-g5howKfpOVdJBq2Xl

Fig. 13: Water in Motor Oil

Fig. 14: Water in Gearcase

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Outboard Motors (3a/7)

Run 4-stroke motor on auxiliary tank filled with gasoline, fuel stabilizer, and some sort of corrosion-inhibiting oil (Yamaha EFI Engine Storage Fogging Oil)

This process will coat all fuel system internals (fuel/water separator, VST, fuel rails, fuel injectors, etc.) and important engine components (valves, pistons, rings, cylinders, etc.) with corrosion-inhibiting oil

Auxiliary tank should be connected upstream of fuel/water separator
Run motor until dense smoke visible out exhaust (typically 1-2 gallons)
Shut off motor and drain fuel/water separator, motor-side fuel filter, and vapor separator tank (VST)
Suggest draining fuel from fuel/water separator, motor-side fuel filter, and VST before priming with fuel concoction from auxiliary tank to reduce run time

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SOURCE: https://www.westmarine.com/west-marine-6-gallon-epa-portable-fuel-tank-20375341.html?srsltid=AfmBOooloMqgHZoMa-Ax4RsB2PKcHmPLYksbnSEqxLjvrJXQwoZ99NOE

SOURCE: https://www.boats.net/catalog-product/collection/yamaha/C279B9B4AE12A1A5CD60C188C7CB80F43CAFDA7C?titan_sku=ACC-STORR-IT-32&gad_source=1&gad_campaignid=17890671044&gbraid=0AAAAAD2tQK_FacIRA5nycOytYYNvViDVQ&gclid=Cj0KCQiApL7KBhC7ARIsAD2Xq3Cq1C2iZ9js3OKTWlXRTf6nj9-SZ-I_zSDvn6yTiCiN3mm-xv2XX1oaAssPEALw_wcB

Fig. 16: Yamaha EFI Engine Storage Fogging Oil

Fig. 15: Auxiliary Fuel Tank

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Outboard Motors (3b/7)

If auxiliary tank unavailable or if 2-stroke motor, use aerosol fogging oil

Note that this step will not coat inside of fuel/water separator, VST, fuel rails, or fuel injectors with corrosion-inhibiting oil
Fuel stabilizer will help fuel from going bad, but will not prevent internal rust from forming if there is significant water contamination

Run motor on boat-side fuel tank (with fuel stabilizer) to circulate through system
If possible, spray fogging oil into intakes/carburetor
Otherwise, remove spark plugs and spray fogging oil for 5sec in each firing chamber through spark plug port
Ensure disengagement of ignition system (remove safety lanyard, disconnect distributor, etc.) before turning key over to circulate fogging oil through cylinders
If 2-stroke motor, drain most (but not all) fuel from carburetor bowl

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SOURCE: https://www.wholesalemarine.com/sta-bil-engine-fogging-oil/?srsltid=AfmBOoqf2jRdCvSdgQi5cuIkdzJpkpLhzSFMIqYlNhZmV2AdPR2bsVKr

Fig. 17: STA-BIL Aerosol Fogging Oil

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Outboard Motors (4/7)

Apply corrosion-inhibitor to motor, tilt/trim rams, and steering rams

This will coat motor exterior and all metal components with corrosion-inhibiter
Preferred product is WD40; however, Yamashield or CRC Corrosion Inhibitor are good alternatives

Remove cowling and apply corrosion-inhibitor to powerhead

All metal surfaces, electrical connectors, brackets, fasteners, etc. are fair game
Avoid spraying rubber components, especially timing belt
WD40 needs heavier coating because it will evaporate (typically use entire can)
Yamashield/CRC needs light misting because of its thicker application

Clean tilt/trim rams and steering rams
Apply corrosion-inhibitor to rams

Avoid spraying rubber seals and wipe off excess if necessary

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Fig. 18: Applying Corrosion-Inhibiting Aerosol to Powerhead

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Outboard Motors (5/7)

Grease all service locations with marine specific grease (Yamalube, Johnson/Evinrude Triple Guard grease, etc.)

Grease all zerk fittings with grease gun

Even new motors can accumulate water around these pivot points
Continue greasing until trapped water and old grease are purged from pivot points
Two zerk fittings typically found in lower cowling (latch handle assembly)
Three zerk fittings typically found on midsection bracket (two on tilt pivot behind steering ram and one on steering bracket pivot)

Grease common locations like tops of tilt rams and ram pads
Remove propeller, clean shaft, and apply grease

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SOURCE: https://www.thehulltruth.com/boating-forum/825055-yamaha-engine-grease-points-grease-use.html

Fig. 19: Grease Points on Yamaha Outboard

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Outboard Motors (6/7)

Lower motor to the full-down position

Gearcase must be stored down to ensure proper water drainage

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Fig. 20: Illustration of Motor in Fully-Down Position

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Outboard Motors (7/7)

Perform battery storage procedure

This helps with longevity of battery and ensures boat will start in Spring

Disconnect battery from motor or turn off battery switch
Either store battery indoors or plug into battery charger/maintainer

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Outboard Motors

Add fuel stabilizer to fuel tank(s)

Check motor oil and gearcase oil for water intrusion. Always good practice to change both; however, only necessary if signs of water intrusion (milky oil).

Apply fogging oil to fuel system and engine

Run 4-stroke motor on auxiliary tank filled with gasoline, fuel stabilizer, and some sort of corrosion-inhibiting oil (Yamaha EFI Engine Storage Fogging Oil or 2-stroke oil)
If auxiliary tank unavailable or if 2-stroke motor, use aerosol fogging oil

Apply corrosion-inhibitor to motor, tilt/trim rams, and steering rams

Grease all service locations with marine specific grease (Yamalube, Johnson/Evinrude Triple Guard grease, etc.)

Lower motor to the full-down position

Perform battery storage procedure

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Inboards/IO Sterndrives (1/3)

All steps for outboard motor winterization are applicable for inboards/IO sterndrives; however, the cooling system is different and warrants additional instruction for flushing procedure

Steps in this section should be performed before/during engine fogging
Fogging should be the last step and may have to be performed near tail end of antifreeze flush

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Inboards/IO Sterndrives (2/3)

Warm up motor and drain cooling system

Run motor on hose until motor is warmed up and thermostats are open
Shut off engine and drain all water out of risers/manifolds by removing drain plug (usually 5 blue plugs to remove, typically located on risers/exhaust manifolds)

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SOURCE: https://www.boatus.com/expert-advice/expert-advice-archive/2018/april/changing-engine-oil

Fig. 22: Illustration of Single-Point IO Drain System

SOURCE: https://www.amazon.com/Quicksilver-8M0119211-Cylinder-Manifold-MerCruiser/dp/B003907WXQ

Fig. 21: Illustration of Drain Plug

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Inboards/IO Sterndrives (3/3)

Flush motor with environmentally safe antifreeze

This prevents catastrophic failure due to expansion of freezing water

Attach flush hose to large container filled with environmentally safe antifreeze
Place container above flush port for gravity feed; otherwise, use transfer pump

Make sure container is properly vented to allow unrestricted flow of antifreeze

Run motor with antifreeze until pure antifreeze comes out of exhaust (usually ~5 gallons)
If using aerosol fogging oil, spray into carburetor/intake (motor stalling is totally fine)
Shut off engine and drain 1/3 of antifreeze out of risers/manifolds in case of residual water in cooling system

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SOURCE: https://www.hardin-marine.com/p-86016-do-it-yourself-winterizing-kit.aspx

Fig. 23: Illustration of Gravity-Feed Antifreeze Flush

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Inboards/IO Sterndrives

All steps for outboard motor winterization are applicable for inboards/IO sterndrives; however, the cooling system is different and warrants additional instruction for flushing procedure

Warm up motor and drain cooling system

Flush motor with environmentally safe antifreeze

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Conclusions

Outboard motors do NOT require antifreeze to prevent catastrophic failure caused by freezing water

Lowering motor to full-down position is the only step required to prevent catastrophic failure

All other outboard motor winterization steps (fuel stabilization, fogging, etc.) are for longevity, not freeze protection

These steps reduce rust, corrosion, fuel degradation, etc. and are important for extended storage, especially in cold weather, to lower long-term maintenance and repair costs

Antifreeze flushing is a mandatory step for inboard motors/IO sterndrives and cooling water systems

Water remains trapped in blocks, risers, manifolds, and cooling lines and must be flushed to prevent catastrophic failure

Winterization procedures depend on engine and cooling system design – there is no one-size fits all approach

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Thank you.

CHRISTOPHER S. THURMAN, PH.D.
THURMAN MARINE SERVICES LLC

PHONE: 757.567.7591

EMAIL: thurmanmarineservices@gmail.com

WEBSITE: https://www.thurmanmarineservices.com/

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