Should you do it yourself or take it to a shop?

When the frost is on the pumpkin, it’s time to prepare your outboard engine(s) for its “long winter’s nap.” It may be tempting just to throw a cover over it and call it a day, but temperatures below freezing can cause costly damage to an engine that isn’t winterized properly in the North. Whether you do the job yourself or take your outboard in for service, spending a little time and money today potentially can save a lot of both come spring.

Why go to a pro?

“The new engines are quite sophisticated and on some of them, the spark plugs can be hard to get to,” says Scott Klein, president of Wendt’s Marine, an award-winning marine service shop in Van Dyne, Wisc. He’s seen what can happen when a DIY’er pulls the spark plugs out of an engine to spray fogging oil or engine oil into the holes, then cross-threads the plugs trying to put them back in. As a result, he says, “The hole is shot and you have to change the head of the engine, which costs about $1,000.”

In addition, Klein says, “When we are running the engines, we might see things that are wrong with them that our customers might not catch. It will cost you a couple of hundred bucks for winterization here, but you might be saving thousands.”

It also can pay to shop around for a marine service facility or marina that offers a “bundle deal” – for example, if you winterize your boat and engine with them, they may give you a break on storing the boat or even shrink-wrap it at a discounted price.

If you decide to go the DIY route with winterization, however, as many outboard owners do, start with your boat and engine on the trailer or remove the outboard and bolt it to a workbench. It will save time to be sure in advance that you have all the tools, hoses, drip pans, and winterizing products you’ll need for the project.

Fill the fuel tank.

Fill Fuel Tank

Putting fresh fuel in the boat’s tank and treating it with marine fuel additives will help the fuel system sit idle until spring without any problems. If you leave the fuel untreated, some of its components inevitably will begin to oxidize and form a gum-like substance. In the spring, when you try to burn this fuel, it can leave deposits in your engine’s combustion chamber, and over time these deposits will build up and reduce the engine’s performance.

“Most of the issues our dealers run into are caused by stale fuel,” says Mercury Technical Service Department Team Leader Ryan Russell. “If the fuel in your tank is more than a month old, pump it out and replace it with fresh fuel.”

As you drain the fuel tank and line, also drain the fuel from your engine, keeping the spent fuel to discard properly (another possible reason to let a service shop do the winterizing for you). After draining the engine, replace the fuel filter so it will be clean and ready to go in the spring.

If possible, refill the tank with ethanol-free fuel such as REC-90, a premium blend formulated specifically for recreational engines. Due to the widespread controversy over the negative impact that ethanol-treated gasoline can have on marine engines, REC-90 is now available at more gas stations in the U.S. and Canada. Stop when the tank is about 95 percent full, because extreme temperature changes over the winter can cause the fuel to expand, potentially forcing gas out of the engine’s overflow vents.

Treat the fuel.


“The best time to treat fuel is when you pump it into your tank, either during your last fill-up of the season or when you replace stale fuel during winterization,” Russell says. He recommends using the Mercury Fuel Care System, which includes Quickare, Quickleen and Quickstor, whether your engine was built by Mercury or another manufacturer. These products are engineered to work together to optimize fuel, remove any leftover deposits from the engine, and protect the fuel system over the winter months.

If your outboard is a four-stroke, after you treat the fuel you should change the oil and oil filter before you run the engine. The goal is to have the whole engine clean and ready to go in the spring.

Next, run the treated fuel through the fuel system for 10-15 minutes to ensure it penetrates every component.

Fog the engine.

Fog the engine

Now that the motor is warmed up, remove the spark plugs and spray 1 oz. of fogging oil (for four-strokes and conventional two-strokes) into the inside of the engine to prevent corrosion. Look for fogging oil that’s specially designed for use during winterization, such as Quicksilver Storage Seal. With direct-injected engines such as Mercury OptiMax, use 1 ounce of DFI engine oil instead of fogging oil. A small oil can with a long flexible neck works best to inject the oil into the cylinders for this application.
Russell also recommends putting a coat of anti-seize lubricant on the plugs’ threads before (carefully) replacing them.


Change the gear lube.

Change gear lube

Check your engine’s lower unit for water; if you find water, be sure to drain it. Water can freeze and expand during storage, potentially cracking the unit. The next step is to change the gear lube and replace it with fresh lube, along with new washers on the fill and vent screws. As you drain the old oil, inspect it carefully. “If it’s milky, it indicates a leak. Take your outboard to the dealer for service,” Russell recommends.

“If we see it run milky, we know you might have a seal out somewhere,” Klein agrees.

“Take care of it in the fall; don’t wait ’til spring,” adds Russell.


Check the prop shaft. 

Prop Shaft

With some gearcases, you will have to remove the propeller in order to change the lube; but even if your engine doesn’t require that, it’s a good idea to pull the prop off anyway. Inspect it for damage and send it to be repaired if necessary. This also is an ideal time to check the shaft for debris and fishing line that might be wrapped around it, which could spoil your whole day at the start of next season. If the prop is okay, either replace it or store it separately from the engine to discourage thieves.


Check the trim fluid.

Trim Fluid

You will need to tilt the engine all the way up to get to the pump. The fluid inside should be bright red; if so, check the level and top it off it it’s low. If the fluid is pink or milky, indicating the presence of water, drain it and replace it, then take your engine to the dealer for service.

Watch “QuickBite Tips: Checking Your Power Trim Fluid”


Lubricate any grease points.

These can vary from engine to engine. Consult your Owner’s Manual to see where your outboard needs grease.


Touch up any nicks or scratches.

Inspect your engine’s lower unit and repaint any wear-and-tear marks with paint from your touch-up kit or matching marine paint.


Check the battery. 

Check Batteries

If it’s a lead acid battery, inspect the fluid level and add distilled water if needed. Be sure the battery is fully charged, remove it from the boat, and store it in a cool, dry place.


Store the engine upright.

At that angle, it’s easier for your outboard’s self-draining system to work all winter. Cover the engine to protect it from the elements. Make sure you rig a prop inside to hold the cover up. “I’ve seen the weight of the snow break a boat’s windshield,” says Klein.

He also advises putting a dryer sheet into your outboard’s engine cowling to prevent tiny mice from climbing in and chewing the wires. “Mice don’t like dryer sheets,” he says. “You just have to remember to get it back out in the spring.”

Follow these tips and in the spring you’ll be back out on the lake casting for fish while some of the other anglers are still turning a wrench or taking their outboards to the shop.


by Louisa Beckett for Mercury Marine –


See also Winterizing your boat and Get Your Boat Cabin Ready for Winter