Step 1: Prep - Gather the key tools and materials
If you’ve been paying the marina $150 or
more to winterize your boat every fall, it’s
time to do the job yourself and save some
dough. We brought in marine mechanic
Sam Kelley to guide you through the process
and share his expert tips for winterizing
an inboard/outboard (I/O) drive boat.
The steps are much simpler for an outboard,
and we’ll cover those in another issue.
An I/O is full of water. So if you don’t
drain the water properly, it can freeze
and cause major damage. However, if
your boat will be in heated storage, you
can skip the draining part.
The job isn’t hard, but we have to warn
you: If you skip a step or miss a drain plug,
you could wind up with a repair bill of at
least $3,000 for a replacement engine. (And
none of that cost will be covered by insurance.)
So if you’re at all nervous, invest in a
factory service manual to locate all the
drain ports and cooling units.
Before you start the winterizing procedure,
pick up a few gallons of RV antifreeze,
a can of fogging oil, motor oil, an
oil filter, lower-unit lube and drain plug
gaskets, an oil suction pump and a lower-unit
lube injection pump. Then gather up
your screwdrivers, sockets and combination
Meet the Pro
Sam Kelley owns Sam’s
Marine and Performance in
Stillwater, MN. He’s been
maintaining, repairing and
upgrades for almost 25
years. We asked Sam to help
with this story because he
winterizes about 150 boats a
year and hasn’t cracked a
Step 2: Change the oil and clean the carb
1 of 2
Photo 1: Change your oil
Yank the dipstick. Then shove the suction hose down the dipstick tube and suck
out all the old oil. Change out the oil filter and then refill the engine with fresh oil.
2 of 2
Photo 2: Spray fogging oil down the carb
Hold the carburetor choke open (if
closed), start the engine and spray
fogging oil directly down the carb until
the engine chokes out.
Start by sucking out the oil and changing
the filter (Photo 1). (Oil suction
pumps can be found at most auto parts
stores.) Then run the boat over to the
marina and top off the gas tanks with
non-oxygenated fuel (if available). Add a
marine fuel stabilizer to the tank and
run the boat to a landing. With the boat
still in the water, remove the spark
arrester from the carburetor and fog the
engine (Photo 2). Then trailer it and perform
the rest of the procedure on land.
Step 3: Drain the coolant
1 of 4
Photo 3: Yank the hull plug
Remove the hull plug with an open or box-end wrench. Don’t use an adjustable
wrench—it will round off the shoulders on the brass plug.
2 of 4
Photo 4: Drain the power steering cooler
Loosen the hose clamp and remove the
drain hose from the power steering
cooler (if it doesn't have a drain plug).
3 of 4
Photo 5: Drain the block
Locate and remove the block drain
plug(s) at the bottom of the block.
Cooling systems always suck in sand,
so as soon as you remove a drain plug,
shove a bent coat hanger inside the
drain port and wiggle it around to
loosen any sand or rust dams.
4 of 4
Photo 6: Flush the engine with RV antifreeze
Pour RV antifreeze directly into the
thermostat opening or into the large
hose attached to it. Keep pouring until
you see a steady stream of the pink
stuff running out of the block drain plug.
Tip the trailer up (so it drains well) and
place a bucket under the hull drain plug.
Then remove the plug (Photo 3).
Hop in the boat and start draining near
the top of the engine. Remove the drain
plugs (or the hoses) for the exhaust manifolds,
power steering cooler (Photo 4), oil
cooler (if equipped) and block drain
plug(s); Photo 5. See “Draining Tip.”
Leave the block drain plugs out,
but reinstall all the other drain
plugs and hoses. Then remove
the thermostat or the hose
attached to the thermostat housing
and pour in RV antifreeze until it drains
out the block drains (Photo 6). Once the
antifreeze stops draining, reinstall the
block drain plugs and the hull drain plug.
Note: Sam likes to leave the engine
block flushed but empty for the winter.
However, some marine engine manufacturers
recommend filling the entire
engine with RV antifreeze. Always follow
your engine manufacturer’s advice.
trying to screw
remove the entire
valve. It’ll drain much
better and the “wings”
won’t break off.
Step 4: Lube the lower unit
1 of 1
Photo 7: Refill the lower unit
Screw in the pump nozzle and pump
in the new lube until it comes out the top
vent. Insert new gaskets in the drain and
vent holes and install the plugs.
Next, unscrew the bottom drain plug on
the lower unit. Allow the lube to drain a
few minutes before removing the upper
vent plug. Once the old lube is out, refill
with fresh lube (Photo 7). Sam recommends
refilling with high-performance lube.
Finally, remove the battery terminals
and give it a full charge. Sam has had
better luck leaving the fully charged battery
in the boat. But you can also bring it
inside and attach a battery maintainer.
Cover the boat and dream about spring.