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How to Fully Winterize Inboard Boat Motors in 4 Steps
It's the end of boating season and time to reluctantly start strapping down those winter boat covers. Then, you'll be moping around winter boat shows to fight the winter boater's blues. Before you get to that, though, there's one crucial thing you have to do:
Winterize your inboard boat motor!
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If you've got an inboard or sterndrive (inboard/outboard) boat motor, winterizing is an absolute must. This process prevents gunk from building up, keeps condensation out of the fuel tank and keeps your engine healthy overall. I've already covered winterizing pontoon boats, which usually have outboard motors.
For those of you with powerboats, here are the steps to winterize your inboard boat motors. I've removed a few steps from the entire boat winterization process here, like removing the battery and keeping it on a trickle charge.
This post focuses specifically on winterizing motors.
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How to Fully Winterize Inboard Boat Motors in 4 Steps
1. Prepare Your Inboard Boat Motor for Winterizing
Fill the tank with gas.
Why do you want the tank filled with gas over winter, you might ask? The answer: This decreases the chance of getting air into the tank. Air is bad for the tank because it brings moisture and, with low temperatures over winter, condensation!
If you don't fill up your tank, you'll wind up with water inside, which can cause severe problems for your engine.
Add the fuel stabilizer (or whatever your boat's Owner's Manual suggests).
I suggest using STAR BRITE EZ-To-Start Fuel Additive. What does a fuel stabilizer do?
The stabilizer prevents buildup in your boat's fuel lines, injectors and carburetors while it sits for long periods.
Warm the engine. You can do this one of two ways: Run the engine while the boat's in the water or run the engine with an adaptor or motor muffs and a hose running the water supply.
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2. Add Antifreeze and Spraying Fogging Oils
After your motor is cleaned and prepared as described above, the first real winterization step is applying antifreeze. The second step is spraying fogging oils into the engine.
Adding Antifreeze
Adding antifreeze to the engine prevents any water condensation or otherwise from freezing. Freezing can be harmful because it means expansion, causing stress and, eventually, cracks. The last thing you need is to find a milky consistency in your oil and to have to call your mechanic.
Don't contaminate where you play. Purchase a non-toxic propylene glycol antifreeze. Avoid ethylene-based antifreeze, as ethylene can release toxins into the water.
Adding Antifreeze to Engine Blocks
You'll want to follow your boat manufacturer's specifications to drain the engine block. Once the engine block is drained of coolant, then you add the propylene glycol antifreeze.
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Adding Antifreeze to Sterndrives
When you hear the word sterndrive, it's important to know what it means. Essentially, a sterndrive is an inboard engine with an outboard drive system. So a sterndrive has to be treated like an inboard engine, but with a few additional steps to protect the lower parts.
To drain the lines, leave the sterndrive stored in a down position. Using your fresh water source (boat hose and faucet), allow your boat's engine to come to temperature. This allows the thermostat to breathe, letting both the coolant and fuel stabilizer circulate through lines, carburetors and injectors.
To make it easy, boaters can purchase DIY kits like this Camco Winterizer Kit.
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Spraying Fogging Oil into the Engine
After applying the antifreeze to your engine, and while it's still warm, the next step is to spray fogging oil into the engine.
Spraying fogging oils into inboard and sterndrive engines slightly differs from spraying it into outboard engines. I suggest the STA-BIL fogging oil. For more information, check out this Gold Eagle's article explaining the product's proper usage.
Continue the process by filling a five-gallon bucket (or the convenient DIY kit mentioned above) with non-toxic antifreeze. Closing the intake seacock, transfer the hose to the bucket.
Letting the boat engine idle, keep watch for the bucket's liquid to reach low levels and the exhaust to discharge the antifreeze. Time it for 30 seconds or until the bucket is nearly dry. Then proceed to fog the carburetor.
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Generously spray the fogging oil.
Engines with high horsepower may sputter, and low horsepower engines may even stall out but that's okay. You should see white smoke. When the antifreeze bucket is finally dry, turn off the engine and re-secure the hose to the seacock.
Alternatively, you can remove each individual spark plug. With the spark plugs removed, you can spray fogging oils directly into the engine's combustion chamber.
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3. Change the Engine's Oil and Replace Oil Filter
Some boaters tend to leave this task until their spring boat inspection. But I say do it now while your engine is already warm. Draining and changing the oil is easier when it's warm.
Your engine and transmission oil could be contaminated with dirt and particles now, which can harm them during winter if not dealt with properly. Start the engine and monitor the fuel filter for leaks using a continuous water supply with your boat still in the water or attached to a standard garden hose.
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If a leak is found, turn off the engine and make proper repairs. Check the installed filter once again. Restart the engine. Keep it at an idle RPM and allow it to reach regular temperatures.
The trick here is to not over-cool the engine. It's better to cool it off gradually over time.
When using a combination hose and adaptor, don't run the faucet at a full-on blast. Cut the faucet off so it's a steady flow.
You should let the engine run for 15 minutes at minimum. This will allow the fuel stabilizer to enter the fuel system. But if this proves difficult or you're in a hurry, at least add an oil stabilizer.
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4. Do a Final Inspection
Almost there! While your hands are dirty, you might as well follow these routine checks.
Check the Exhaust System for Corrosion
Inspect your exhaust system by disassembling it from the water lift muffler. In general, look it over for anything suspicious, like corrosion and buildup. Make sure the raw water injection hose hasn't become obstructed in any way.
Inspect Hoses and Hose Clamps
Hoses and hose clamps can often become damaged. Check them over to make sure they're not cracked, shredded or rusty. If they are, be sure to replace them now before you forget come spring!
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Seal Off Cracks from Air Intake
If you find any openings, seal them up! Cracks and openings allow the build-up of damp air and water condensation. Double-check your air inlet and exhaust outlets. You can use simple tape to secure them. Here are some last-minute things to mention, just so you don't forget basic boat winterizing steps:- Take care of the battery. Remove and keep it indoors at home, or leave it installed and hook it up to a trickle charger.
- Consider pests. Whether you keep your boat on the lift or in storage, plan accordingly with pest controls and repellants.
- Invest in a quality winter boat cover. It may be handy to also invest in a dehumidifier and boat cover support poles. There's more information on covers and poles for winter coverage here.
- Invest in theft prevention. Stay vigilant and stop by to check on your boat every once in a while.
What are you waiting for? If winter is looming, or if you're expecting some unseasonably cold weather in your area, it's time to winterize your inboard boat motor. Come next spring, you'll find your boat in tip-top shape.
After a quick spring boat inspection and some de-winterization steps, all you have to do is grab the cooler and take the family out for some fun on the water.
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