Guide
Honda BF Outboard Winterization: The Basics
Honda Marine produces exclusively four-stroke outboards under the BF designation — from the compact BF2 and BF2.3 portables up to the BF250 and BF350 performance models. All BF motors share a common design philosophy: a traditional four-stroke engine with a SOHC or DOHC valvetrain, raw water cooling, and a lower unit with a single-piece gearcase.
Because Honda does not produce two-stroke outboards, winterization for BF series motors follows a consistent set of steps across the range: freshwater flush, cylinder fogging, gear oil change, fuel stabilisation, and pre-storage checks. The specific service intervals, oil grades, and torque specifications vary by model — always use the Honda Marine service manual for your BF model.
Honda BF models used in salt water require the same freshwater flush as any other outboard. Honda's VTEC-equipped models (BF115, BF135, BF150) have an additional variable valve timing system that should be noted in the service manual check. The BF200, BF225, BF250, and BF350 use a V6 configuration and may have additional service items — again, refer to the Honda Marine dealer service guide for large V6 models.
Guide
Flushing the Honda BF Cooling System
Honda BF outboards are cooled by raw water drawn through the lower unit intake. Salt, mineral deposits, and biological growth accumulate in the cooling passages over a season of use and must be flushed out before storage.
Honda provides a flush port on many BF models — a threaded port on the lower section of the motor that accepts a garden hose fitting. Using the flush port allows you to run fresh water through the cooling system without starting the engine, which is convenient for end-of-season maintenance in a boatyard. For BF models without a dedicated flush port, use flush muffs placed over the lower unit water intake, start the engine, and idle for two to four minutes until water runs clear from the exhaust.
After flushing, tilt the motor to the full up position and allow it to drain. Listen to make sure water stops dripping from the exhaust passages before you move the motor or begin other winterization steps. Residual water pooling inside the cowl or exhaust passages can cause corrosion at contact points during storage.
Guide
Cylinder Fogging: Honda BF Four-Stroke Method
All four-stroke Honda BF outboards benefit from cylinder fogging before winter storage. Fogging oil creates a protective film on cylinder walls, piston rings, and valve seats that resists moisture and prevents the surface corrosion that can cause starting problems in spring.
For Honda BF EFI models (which includes all current mid-range and large BF outboards), the fogging oil is sprayed into the throttle body air inlet while the engine is idling, then the engine is shut off immediately to trap the oil inside. For carbureted BF models (typically smaller portable models such as BF5, BF8, BF9.9), the fogging oil can be sprayed directly into the carburettor air intake using the same procedure.
Honda recommends Honda Genuine Engine Storage Fogging Oil or an equivalent marine-grade storage oil. After applying fogging oil and shutting the engine down, plug the air intake with clean foam or a cloth to prevent moisture from entering the intake during storage. Remove this plug before attempting to start the engine in spring — leaving it in place will prevent the engine from starting and can damage the air filter.
Guide
Honda BF Lower Unit Gear Oil Service
The lower unit of a Honda BF outboard contains the bevel gears, prop shaft, and forward/reverse gear shift mechanism, all lubricated by gear oil. Honda recommends draining and replacing the gear oil annually, and the before-storage timing allows you to catch water contamination in the oil before it causes internal damage.
Honda specifies their Genuine Gear Oil for BF outboards — check your owner's manual for the correct specification and fill volume for your model. The drain procedure follows the standard two-plug sequence: remove the lower drain plug first to drain, then fill from the lower plug until oil flows from the upper vent plug. This sequence ensures no air pockets remain in the gear housing.
If the drained gear oil appears milky, foamy, or distinctly lighter in colour than fresh gear oil, there is water ingress. The likely sources are a worn propeller shaft seal, a damaged driveshaft O-ring, or a failed shift rod seal. Have the source identified and the seals replaced before storing the motor for winter. Water left in the gear housing will freeze, expand, and may crack or deform the lower unit housing.
Guide
Fuel System Care for Honda BF Outboards
Honda BF outboards with EFI — which covers all current BF75 and larger models, and most BF40 and up — have electronic fuel injection systems where untreated fuel can varnish injectors and create hard starting or rough running conditions after months of storage. E10 ethanol fuel is particularly problematic, as it absorbs moisture and breaks down in storage.
Honda's recommended approach for fuel-injected BF models is to add a Honda-approved fuel stabiliser to the tank, run the engine briefly to circulate stabilised fuel through the injection system, and then leave the stabilised fuel in the tank. Complete draining of the high-pressure fuel rail is not a straightforward DIY procedure on EFI models — stabilisation is the standard approach.
For carbureted Honda portable models (BF2, BF2.3, BF4, BF5, BF6 series), draining the float bowl is straightforward and preferable to stabilisation for short-season storage. The drain screw is located on the bottom of the carburettor float chamber — refer to the service manual for its location on your model. Drain the carburettor with the fuel cock closed, then run the engine briefly on the residual fuel in the bowl to empty it completely.
Guide
Pre-Storage Checks and Land Storage Setup
Before covering a Honda BF outboard for winter, complete these final checks: inspect the propeller for nicks and bent blades; check the lower unit anode (usually a zinc or aluminium bar on the anti-ventilation plate) and replace if more than 50 percent consumed; spray all external electrical connections, tilt mechanism, and clamp screws with a marine corrosion inhibitor; and check the steering and throttle linkage for smooth operation.
For boats stored with the Honda BF outboard mounted on the transom, the boat must be correctly supported on land. An improperly supported hull can flex over winter — particularly if the ground freezes and thaws, causing support points to shift. This can stress the transom and the motor mount bracket.
KIPAC CE-documented boat stands are designed for long-term outdoor land storage. Position them at the hull manufacturer's recommended support points — typically beneath the keel and along the bilge stringers. Leave the Honda outboard tilted fully up during storage to drain any remaining water from the lower unit and driveshaft area. For Honda portables removed from the boat for storage, use a proper outboard motor stand rated for the weight of your BF model.
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View equipment →FAQ
FAQ
Yes. All Honda BF four-stroke outboards — from small portables to large V6 models — benefit from cylinder fogging before storage. The fogging oil protects cylinder walls and valve faces from corrosion during periods of inactivity. The application method varies slightly between carbureted and EFI models — check your owner's manual.
Honda recommends Honda Genuine Gear Oil for BF outboard lower units. Refer to the owner's manual for your specific model to confirm the correct specification and the fill volume in millilitres or ounces. Using an incompatible aftermarket gear oil may affect gear lubrication and warranty claims.
Two to four minutes of idle flushing with fresh water is typically sufficient, or until the water running from the exhaust is clear. Honda models with a dedicated flush port can be flushed without running the engine — the flush port circulates water through the cooling passages directly.
A properly winterized Honda BF outboard mounted on a boat can be stored outdoors if the boat is correctly supported and the motor is covered. The key is that all water has been drained from the cooling system, the fuel system is treated, and a weather cover protects the motor cowl. In locations with severe frost, indoor or covered storage is preferable.
Yes. Disconnect the battery from the engine harness before storage to prevent parasitic drain from the engine management electronics. Store the battery in a cool, dry location and keep it on a maintenance charger to preserve capacity over winter.
