The eight steps are the same for every outboard. What changes brand to brand is which fluids go in and a few details about how the engine is built. This is the Mercury and Mariner version. Running a MerCruiser sterndrive instead? That one is here. For the general walkthrough, start with the boat winterization guide.
What your Mercury needs
- Mercury and Quicksilver fuel additives
- Fogging oil
- Spark plugs
- Mercury 4-stroke engine oil or Mercury 2-stroke oil
- Mercury oil filters
- Mercury and Mariner fuel filters and water separators
- Mercury gear lube
- Mercury and Mariner water pump and impeller kits
- Quicksilver marine grease
- Mercury and Mariner anodes
Know which additive you are reaching for
Mercury and Quicksilver sell a storage stabilizer, a fuel system cleaner and an engine decarbonizer, and they are three different products for three different jobs. The stabilizer is the storage one and it is what goes in before the last run. The cleaner is a season-long product. The decarbonizer is a treatment you run through a running engine.
Dose the tank, run it long enough that treated fuel has reached the water separating filter and the injectors or carburetors, then shut it down and change the fuel filter.
Fog it, then new plugs
Fog the engine until it smokes and stalls, then install new plugs. In that order. Fogging fouls whatever is in there, so plugs installed first are already spent by spring. On a carbureted two stroke, drain the carburetor bowls after the fogging run. Fuel left standing in a bowl all winter turns into varnish, and varnish in a Mercury carb is a spring rebuild.
Oil and filter, four strokes
Change it warm, right after fogging, so the acid and water come out with the oil. Mercury four strokes want a Mercury or Quicksilver FC-W marine oil in the weight your manual calls for, plus a new oil filter. Verado and the supercharged engines have their own requirements, so check the book rather than assuming.
Two stroke? Skip the oil change and check your TC-W3 supply instead. If you run an oil injected engine, top the reservoir before storage rather than after.
Lower unit, and the two gaskets everybody reuses
Pull the lower screw and read what comes out before you plan the refill. Clean lube is the color it went in. Milky means water past a seal, and that is a repair to book now instead of discovering in May. Glitter means wear inside.
Refill with Mercury gear lube from the bottom until it comes out the vent, then close the vent screw first. Mercury specifies different lubes for different gearcases, and the high performance one is not just a marketing name, so match it to your manual.
Both screws take a new sealing washer. Two cheap parts, and the most skipped item on this list every year. Reusing crushed washers is exactly how water gets into a gearcase over a winter. They are specific to your model, so send us your model and serial or call and we will match them.
Impeller
The impeller is a wear item on a schedule. Mercury is more aggressive about this than most, so read what your manual says for your engine rather than going by what a friend does. Then pick an end of the season and be consistent about it.
The argument for fall is that you are already in the lower unit for the gear lube, and a marginal impeller shows itself in your driveway in October rather than at idle in a no-wake zone in May.
Buy the full water pump kit, not the bare impeller. The wear plate, housing and seals in the kit are why people end up doing this job twice.
Finish it
- Grease the steering, the tilt tube and the prop shaft with marine grease
- Check the anodes. More than half gone means replace now, not in the spring queue
- Battery off the boat, terminals cleaned and coated, on a maintainer if you have one
- Store the engine tilted all the way down so the gearcase drains
- Cover it, and vent the cover
Not sure which gear lube or filter your engine takes? Call us at 631-722-5700 or send us your model and serial number. Always check your Mercury owner's manual for capacities and service intervals for your specific motor.