Boat Winterization Guide

Winterizing is not complicated, but the order matters, and a couple of the steps get skipped every year because they are small and cheap and easy to talk yourself out of. This is the whole job, start to finish. Below it you can jump to the version written for your engine, with the exact products that brand calls for.

Do it while it is still comfortable outside. Most of this happens with the engine running, which is a much better afternoon in October than in December.

1. Stabilize the fuel, before the last run

Fuel is the first thing to go bad in storage and the most expensive to fix in the spring. Ethanol gas pulls in moisture over the winter and separates. Diesel grows things.

Treat the tank before your last run of the season, not after the boat is on the trailer. The stabilizer has to circulate through the lines, the filter and the carburetor or injectors to do any good, and that only happens with the engine running.

Leave the tank close to full. Air space is where condensation comes from.

2. Fog the engine, then put in new plugs

With the engine still running on treated fuel, fog it. Fogging oil coats the cylinder walls and the internals with a film that stops surface rust while the engine sits.

  • Spray fogging oil into the intake until the engine smokes and stalls
  • Once it is shut down, install new spark plugs

New plugs go in after fogging, not before. Fogging an engine fouls whatever plugs are in it, so anything you install first is already spent by spring.

3. Change the oil while it is warm

Used oil holds acid and water, and leaving it in the crankcase all winter is how you get corrosion that was entirely avoidable. Change it warm, right after the fogging run, so it drains clean and carries the contaminants out with it.

Two-stroke owners, this one is not yours. Check your 2-stroke oil supply instead and move on.

4. Drain the lower unit, and read what comes out

This is the step that tells you whether you have a problem. Pull the drain screw and watch what comes out before you think about the refill.

  • Clean gear lube is the color it went in
  • Milky or cloudy means water got in past a seal. That is a repair to book now rather than discover in May
  • Metal glitter in the lube means something inside is wearing

Refill with gear lube from the bottom screw until it comes out the top, then close the top screw first.

Replace both drain screw gaskets. Two little washers, a couple of dollars, and they are the single most skipped item on this list. Reusing crushed gaskets is how water gets into a lower unit over a winter, which is the exact failure the drain was supposed to warn you about. They are specific to your engine, so send us your model or call and we will match them.

5. The water pump impeller

The impeller is a rubber vane pump, and it is a wear item, not a lifetime part. Most manuals put it on a schedule of every one to three years depending on the engine and how you run it, so check yours.

You can do it at winterization or at spring commissioning. Both are correct and it mostly comes down to which end of the season you would rather find a problem. Two arguments for doing it now:

  • On an outboard you are already in the lower unit for the gear lube, so a lot of the work is shared
  • An old impeller sits all winter with its vanes bent in one direction and takes a set. If it was marginal in the fall it will be worse in the spring, and you will find that out on the water

Shop outboard impellers and water pump kits or sterndrive and inboard impeller kits. Buy the kit rather than the bare impeller if one is offered. The wear plate, housing and seals in there are the reason people end up doing the job twice.

6. Inboards and sterndrives: get the water out

Outboards drain themselves when you tilt them down. Anything with a closed or raw water cooling circuit does not, and water left in a block that freezes will crack it.

  • Drain the block and the manifolds at every drain point, not just the easy ones
  • Run non-toxic antifreeze through the raw water circuit until it comes out the exhaust at full strength
  • Plan on three to four gallons for a typical sterndrive

Pink antifreeze is the non-toxic kind and it is what belongs in a raw water circuit. Automotive green is a different product and does not go here.

7. Battery out, anodes checked

A battery left connected all winter will find something to drain into, and a dead flat battery usually does not come back.

  • Disconnect it and take it off the boat
  • Clean the terminals and coat them
  • Keep it somewhere it will not freeze, on a maintainer if you have one

While you are back there, look at the anodes. Anything more than half gone should be replaced before spring, and doing it now means one less job in the yard when everybody else is waiting on the same parts.

8. Cover it so it breathes

However the boat is stored, water that sits is the enemy. Cover it so it sheds, and so air can still move underneath.

A wrap with no vents is a greenhouse. Whatever moisture is in there in November is still in there in April, on your upholstery.

The short version

  1. Stabilizer in the tank, run it through
  2. Fog the engine, then new plugs
  3. Oil and filter while warm
  4. Lower unit drained, read, refilled, new gaskets
  5. Impeller, now or in the spring, but on a schedule
  6. Antifreeze through the cooling circuit if you have one
  7. Battery out, anodes checked
  8. Covered and vented

Now do it for your engine

Every brand does a few of these steps differently, and every brand wants its own oil, gear lube and additives. Pick yours and we will tell you exactly what it takes.

Everything on this list is in our winterizing section. If you are not sure which product fits your engine, call us at 631-722-5700 or send us your model and serial number. We would rather answer the question than have you buy the wrong gear lube.