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How to Winterize a Boat Motor: A Step-by-Step Guide

For many boaters in the northern hemisphere there comes a time in the fall when we have to admit that it’s time to winterize our boat. We’ve dragged out as many glorious days boating as we possibly can and it’s now time to reluctantly tuck her up until the spring. Winterizing a boat involves protecting it from the effects of water damage, either from mold growth or through the damaging effects of freezing water. While the extent to which you need to winterize your boat depends of the severity of the conditions where you live, there are some basics to getting a boat ready for winter that everyone will need to consider. In a previous guide we looked at how to winterize your boat in general, from cleaning it thoroughly, to draining all the systems, covering it and preparing the engine for winter.

Here we take a closer look at the steps you need to take to winterize a boat engine:

  1. Do you need to winterize a boat motor?
  2. Step-by-step guide to winterizing an outboard motor engine
  3. Step-by-step guide to winterizing an inboard motor engine
  4. Should I drain the antifreeze after winterizing my boat?
  5. What is the difference between coolant and antifreeze?
  6. How Can I Winterize My Boat in an Eco-Friendly Way?

abandoned ships in the snow

Do You Need to Winterize a Boat Motor?

The simple answer is yes. To protect your boat’s motor during the colder winter months there are some steps you’ll need to take to ensure that the damaging effects of water won’t ruin arguably the most expensive part of your boat. When a motor isn’t winterized, water may be left in certain parts which, when temperatures drop below zero, can freeze and expand, creating pressure on those parts of the motor. As this freezing and thawing action occurs multiple times over the winter, this can make the problem even worse. 

However it isn’t just freezing water that causes damage. Water in general, as well as high humidity levels in winter months, can cause corrosion to parts of the motor. While it might seem at first like a lot of work, winterizing your boat isn’t complicated, and it’ll keep your motor healthier for longer. 

There are three main steps for winterizing all boat motors:

  1. Change the Oil and Oil Filter: Impurities and moisture in the motor’s oil can cause damage over the winter, so an important step is changing the oil and filter. Once you’ve changed them, run the motor for a few minutes to circulate the new oil throughout all the parts. 

  2. Change the Fuel Filter and Stabilize the Fuel: Over winter the ethanol in gasoline can absorb water and cause it to separate from the gas, causing corrosion in the fuel tank. One way to overcome this is to empty all the gas from the fuel tank as part of the winterizing process. If that isn’t possible, the best alternative is to fill the fuel tank almost to the top and add a stabilizer which prevents oxidization. 

  3. Drain the Water from the Engine and/or Use Antifreeze: This is the most important step in winterizing a boat motor, and varies depending on whether you have an inboard or outboard motor. 

 

Step-by-Step Guide to Winterizing an Outboard Motor Engine

  1. Flush the motor with fresh water: The engine needs to be flushed thoroughly according to manufacturer’s instructions – either by running it in clean, fresh water or by adding a hose that can flush without the engine on. 

  2. Drain and replace the engine oil and filter: Flush out and change the oil (for four-stroke outboards) and the lower unit gear lube (for all outboards). Run the engine first to ensure any contaminants are picked up in the oil.

  3. Change the oil in the gear case: For the same reasons you’ll want to change the oil in the gear case and replace the seals on the drain plugs. Next spray it with fogging oil to prevent rusting.

  4. Empty the gas tank: You can either empty the gas tank completely or fill it almost full and add a stabilizer.

  5. Add fogging lubricants: A thin layer of lubricant helps prevent against corrosion or the bearings, seals and rotating surfaces. With the engine running, inject fogging oil through the carburetors or electronic fuel injection system to ensure it gets into all parts. 

  6. Cover the engine: If possible use a waterproof tarp or canvas to cover the engine for added protection against the elements. 

  7. Store the engine: If your engine is a small outboard then consider taking it home with you to store in a dry place. Otherwise store it in the running position (ie tilted down) to prevent water ingress.  

honda boat motor

 

Step-by-Step Guide to Winterizing an Inboard Motor Engine

While the main idea is the same when it comes to winterizing an outboard motor versus an inboard motor, there are some differences in the approach. While outboard motors are attached to the stern of the boat, and small ones are even easily removed, inboard motors are found in the hull of the boat, either in the bilge or, for much larger boats, their own separate engine room.

Here we are focusing on do-it-yourself winterizing of inboard engines as many larger boats will leave it to professionals. 

  1. Flush the motor with fresh water: The engine needs to be flushed thoroughly according to manufacturer’s instructions – either by running it in clean, fresh water or by adding a hose that can flush without the engine on. 

  2. Drain and replace the engine oil and filter: Flush out and change the oil according to manufacturer’s instructions. Run the engine first to ensure any contaminants are picked up in the oil. Be as thorough as possible as even small pockets of water can cause expensive cracks.

  3. Remove the spark plugs: This is a good time to change them if required as part of your on-going maintenance schedule, and add some oil inside the cylinders.

  4. Add antifreeze: At this point you’ll want to fill the cooling system with a good quality antifreeze to help against the effects of freezing water. Make sure you have enough antifreeze before starting (at least two gallons but even as much as five). With the intake hose in the bucket, run the engine on idle until antifreeze discharges from the exhaust outlet.  

  5. Add fogging lubricants: A thin layer of lubricant helps prevent against corrosion or the bearings, seals and rotating surfaces. With the engine running, inject fogging oil through the carburetors or electronic fuel injection system to ensure it gets into all parts. 

  6. Cover the boat: In our guide how to winterize your boat we looked at the pros of covering your boat throughout the winter months, and the different options there are for doing so. These include plastic tarps, canvas tarps, fitted covers and shrink wrapping.  

 

FAQs on  How to Winterize a Boat Motor

Should I drain the antifreeze after winterizing my boat?

While antifreeze isn’t as toxic or damaging to the environment as coolant, you’ll still want to get it out of the engine in a safe way and flushing it into the water isn’t recommended. The simplest and safest way to do it is to place the engine intake hose in a full bucket of fresh water, start the engine and let it run. You can then catch the exhaust water as it comes out.

 

Are coolant and antifreeze the same thing?

Despite often being confused as the same, they are in fact two very different products and used differently. The engine coolant’s main function is to better cool the engine by raising the boiling point of the cooling water in the engine. It is made from ethylene glycol and is highly toxic and needs changing every few years as opposed to being added annually like antifreeze. Antifreeze is a blend of propylene glycol and water used for preventing freezing in boat systems and is not dangerous like coolant. 

 

How Can I Winterize My Boat in an Eco-Friendly Way?

Winterizing products are notoriously unfriendly to the environment, but there are some ways you can limit the negative effects. The best antifreeze to winterize a boat engine environmentally is a less toxic propylene glycol antifreeze which is less harmful to marine life. When flushing the antifreeze try and catch it in a bucket to dispose of safely (talk to your local marina about disposal of hazardous wate) rather than letting it discharge overboard. Likewise, when using oils you can use an absorbent pad under your work area to catch spills and drips, as well as working with smaller containers of hazardous fluids – accidents happen and smaller containers mean smaller spills. 

 

Written By: Samantha Wilson

Samantha Wilson has spent her entire life on and around boats, from tiny sailing dinghies all the way up to superyachts. She writes for many boating and yachting publications, top charter agencies, and some of the largest travel businesses in the industry, combining her knowledge and passion of boating, travel and writing to create topical, useful and engaging content.

More from: Samantha Wilson


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