How to Winterize a Boat




About: I am a Middle School Technology Education teacher in southern Wisconsin.

This Instructable will teach you how to prepare a boat for a harsh mid-western winter.

Here's what you need:

  • Combination screw driver
  • A boat - in this case it is a '97 Malibu Response with a Black Scorpion engine
  • Anti-freeze, 3-5 bottles
  • A garden hose connected to a spigot
  • A 5 gallon bucket, ours has 2 feet of hose to attached near the bottom for draining
  • MerCruiser marine oil, oil filter, and oil filter wrench (optional, but since you're there you might as well do that too.)

Also pictured is a prop-puller and socket. This is not need for this instructable.

Step 1: Find the Hose

This boat in an Inboard, which means the engine is located in the center of the boat. Whereas outboard motors are mounted to the back of the boat.

Lift the engine hood and locate the water coolant hose. In this boat it is located on the driver side of the engine. It is the black hose with a brass fitting and a green stripe.

Loosen hose clamps with a screw driver and remove from brass fitting.

Step 2: (Prepare To) Start Your Engine...

Insert a garden hose into the water intake hose of the engine.

Turn the garden hose on before starting the engine. And let the engine idle until the water coming out of the back of the boat feels warm. 5-10 minutes.

As the engine heats up, open and prepare the bottles of anti-freeze.

Step 3: Adding the Anti-Freeze

When the water feels hot, it is time to remove the garden hose. Immediately, pour the anti-freeze into the same engine hose while the engine is still running.

Continue to pour anti-freeze until it pours out the back of the boat. Then shut off engine. Our boat used about 4 bottles of anti-freeze.

Replace the engine hose onto the brass fitting, which is much easier said than done.

Your boat is now ready for another cold winter. Don't forget to remove the battery and maintain the charge a couple of times over winter.

Winterize Challenge

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Winterize Challenge



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    8 Discussions


    3 years ago on Introduction

    I do mine very similar, except I have a inboard outboard, warm engine then run about 4 gallons antifreeze while watchin temp gauge, rv antifreeze doesn't have any coolant properties and will over heat a engine, them I usually place a 100 watt light bulb plugged in in engine compartment for a little heat. the last few yrs Ive been using a ceramic heater also because the newer bulbs don't last all winter here

    hey, great method for filling the antifreeze. I would add this caution to those using this method, there is antifreeze that is not "guaranteed" if mixed with any amount of water, ie. not 100% antifreeze. I've a 5.0 L merc inboard that my father in law "winterized" for me and, in the end, it cost me $6000 to dig my way out of that ruined engine. He added 3 gallon bottles and it didn't come close to displacing all of the water. So, 7 freeze cracks and blow outs later the engine was toast -- and it only dropped down in the teens over the winter. So be forewarned if you don't have enough antifreeze to offset the total coolant volume in you engine, you may be asking for a "titanic" sized problem next spring.....


    4 years ago

    Any chance y'all are fans of a comedy show on satellite radio? I posted your 'ible as the East Coast had it's first blast of cold and freezing stuff coming out of the sky. Oddly enough N.Y.C. was warmer than Nashville!

    1 reply

    4 years ago on Introduction

    Thanks. Also I've googled a bit about how it works. This is very intersting, I never thought boats will interst me one day :-)


    4 years ago on Introduction

    This is the same as a car but a boat needs much more antifreeze. Does a boat don't have a radiator cap to pour the antifreeze?

    1 reply

    Reply 4 years ago on Introduction

    Boats suck up the water they are in to cool the engine with the help of an impeller. The point at which I disconnected the hose is basically when the water enters the system. If you look at Step 2 picture 2, the right angle downward is the intake of the cooling system. Thanks for the question. I hope it helps.


    4 years ago on Introduction

    Great tips! Do you have any suggestions for any non-mechanical maintenance? Like weather protection (if kept outside), etc?