How To Winterize A Boat

Chris Riley by Chris Riley Updated on April 30, 2020. In

Winterizing A Boat

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BRRR – It’s Almost That Time Again!
How To Winterize A Boat

With the boating season winding down in most parts of the country, it’s time to start thinking about protecting your valuable recreational asset. Winterizing a boat reminds me of the old commercial that says “pay me now or pay me later.” The time and effort you spend now will have a definite effect on your boat’s performance, or lack of it, and certainly save you time, effort and money come spring. You should remember that your insurance policy may not cover damage done by lack of maintenance or neglect. That’s why you should take winterization seriously.

The best place for your boat to be during the winter is out of the water, under cover, in a climate-controlled boat storage area. This, however, can be expensive. If don’t have this option perhaps you should consider shrink-wrapping your boat. This, too, is a little expensive but provides a very protective cover. Short of these two items, make sure that your boat is well covered with a tarp or a sturdy specialist boat cover.

Your first step in winterizing should be to make a checklist of all items that need to be accomplished. Check the owner’s manual of your boat and motor(s) for manufacturer’s recommendations on winterization. If you are a new boat owner, perhaps you ask a friend with experience in winterizing for help, or hire a professional to do the job. The following is a generic outline of areas which should be of concern to you, however, there are many resources on the Internet with more detailed and specific information. Naturally, your boat’s motor is a good place to start proceedings.

How To Winterize A Boat Motor

Inboard Engine You should run the engine to warm it up and change the oil while it is warm. This tends to allow impurities to be drained away with the oil. You should also change the oil filter(s). Flush the engine(s) with fresh water. You should circulate boat antifreeze through the manifold by using a pickup hose from the waterpump to a bucket of antifreeze. Start the engine and allow the antifreeze to circulate until water starts to exit the exhaust. This process will vary slightly depending on whether you have a “Raw Water” cooling system or an “Enclosed Fresh Water” cooling system. While you’re in the engine room you should also change the fluid in your transmission. Remove spark plugs and use “fogging oil” to spray into each cylinder. Wipe down the engine with a shop towel sprayed with a little fogging oil or WD-40.

Stern Drive – You should thoroughly inspect the drive and remove any weeds or barnacles from the lower unit. Drain the gear case and check for excessive moisture in the oil. This could indicate leaking seals and should be repaired. Clean the lower unit with soap and water. Check with your owner’s manual for additional recommendations by the manufacturer.

Outboard Engine – Flush engine with fresh water using flush muffs or similar device attached to the raw water pickup. Let all water drain from the engine. Wash engine down with soap and water and rinse thoroughly. Disconnect fuel hose and run engine until it stops. It is important to follow a step by step process to make sure that all fuel is drained from the carburetor to prevent build-up of deposits from evaporated fuel. Use fogging oil in the cylinders to lubricate the cylinder walls and pistons. Apply water resistant grease to propeller shaft and threads. Change the gear oil in the lower unit. Lightly lubricate the exterior of the engine or polish with a dedicated marine product.

Other Important Areas To Protect

Fuel – Fill your fuel tank(s) to avoid a build up of condensation over the winter months. Add a fuel stabilizer by following the instructions on the product. Change the fuel filter(s) and water separator(s).

Bilges – Make sure the bilges are clean and dry. Use soap, hot water and a stiff brush to clean up any oil spills. Once the bilges are nice and clean, spray them with a moisture displacing lubricant and add antifreeze to prevent any water from freezing. Use a bilge pump to remove any excess water.

Fresh Water System – Completely drain the fresh water tank and hot water heater. Isolate the heater by removing the hoses and connecting them together. Pump a non-toxic boat antifreeze into the system and turn on all the facets including the shower and any wash-down areas until you see the antifreeze coming out. Also put non-toxic antifreeze in the water heater.

Head – Pump out the holding tank at an approved facility. While pumping, add fresh water to the bowl and flush several times. Use Vanish crystals or whatever your owner’s manual recommends and let sit for a few minutes. Again add fresh water and pump out again. Add antifreeze and pump through hoses, holding tank, y-valve, macerator and discharge hose. Again, check your owners manual to make sure that an alcohol-based antifreeze won’t damage your system.

Interior – Once you have taken care of the system you should remove any valuables, electronics, lines, PFD, fire extinguishers, flares, fenders, etc. Over the winter these items can be cleaned, checked and replaced as necessary. Open all drawers and lockers and clean thoroughly. Turn cushions up on edge so that air is able to circulate around them or, better yet, bring them home to a climate controlled area. Open and clean the refrigerator and freezer. To keep your boat dry and mildew-free you might want to install a dehumidifier or use some awesome commercially-available odor and moisture absorber products.

Batteries – While it should be obvious, don’t forget to disconnect any batteries if you’re planning on storing your boat over the winter. It’s important to hook you’re your batteries up to dedicated marine battery charger and tender devices to keep them strong and healthy for next season.

Out of Water Storage – Pressure wash hull, clean barnacles off props and shafts, rudders, struts and trim tabs. Clean all thru-hulls and strainers. Open seacocks to allow any water to drain. Check for any blisters and if you find any that look unusual, open them so they can drain a little over the winter. While you’re at it, why not give the hull a good wax job?

In Water Storage – Close all seacocks and check rudder shafts and stuffing boxes for signs of any leaks, then tighten or repack as necessary. Check your battery to make sure it is fully charged, clean terminals, add water if necessary and make sure your charging system is working. Check bilge pumps to ensure they are working and that float switches properly activate the pumps and that they are not hindered by debris. Make sure either to check your boat periodically or have the marina check it and report to you. If in an area where the water you are docked or moored in actually freezes, you should have a de-icing device or bubbling system around your boat.

By following some of the above suggestions, and suggestions given from the links provided, you should be in good shape for the winter. Do not, however, neglect to consult your owner’s manuals for manufacture’s recommendations on winterizing your boat and other systems. If you have not done a winterization job before or don’t have an experienced friend to rely on seek out a professional to do the job for you.



  • Alice Carroll on August 20, 2020

    Thanks for the remind that changing the fluids in my boat is crucial when preparing for the winter. I recently bought my boat about three months ago so I’m not that familiar yet with the necessary maintenance it needs. I hope that I can find a service that give a boat motor engine flush so that I can see for myself how the replacing of the fluids happen.


  • Robert on December 3, 2020

    Great article.

    Winterization will cost you less than having the burden of repairs after winter. How much does it cost to winterize a boat is not the right question to ask, but how much can you save by winterizing your boat. You don’t only save yourself from the costly repairs; you also keep your boat’s extended life for a longer time. Having a DIY winterization process can keep your financial worries at a minimum.

    Use a high-quality antifreeze for boats. Change the oil of your engine before winter kicks in. A warm engine helps flush out the old oil. Disconnect the batteries of your boat. Removing and storing them in a warmer location can maintain its condition for a good time. Get a durable boat cover. It may be expensive, but this is a significant investment you can bank on.


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