How to Winterize Your Boat Engine

Boats properly stored ashore and winterized are more likely to be damage-free and ready to hit the water next spring. 

There’s a lot to consider when it comes to storing your boat for winter, from whether to store it ashore versus in the water, what kind of cover to use, how to properly prep your engine and plumbing, and so on. 

In this article, we’ll focus on how to winterize an outboard engine. 

Water expands when it freezes; not properly winterizing your engine can lead to a cracked block, necessitating engine replacement. No one wants to kick off the spring boating season with a new engine purchase! 

3 Essential Steps to Winterizing Your Boat Engine—No Matter Your Engine Type 

1. Change the oil and oil filter 

1. Change the fuel filter and stabilize the oil 

1. Drain the water from the engine or use antifreeze 

Winterizing an Outboard Engine 

Many of today’s outboard engines—especially four-stroke and direct injected two-stroke outboards—have special winterizing, flushing, and maintenance instructions. Always consult your owner’s manual or service manual before you winterize an outboard engine. 

If your engine is still under warranty, and you don’t winterize it according to the manufacturer’s instructions, you could easily void the warranty coverage. 

For older outboard engines, there may be some variance, but the winterization basics are the same. 

First, change your oil and oil filter to prevent contaminants or residual moisture from corroding your outboard engine in storage. A good multipurpose funnel or a set of different funnel sizes is handy to have here.

Next, flush your engine according to the manufacturer's instructions. Sometimes, this doesn’t involve running the engine at all; newer engines have a garden hose fitting that allows for a quick flush without starting the engine. Otherwise, run the engine for about ten minutes and use a flush-muff device (motor flusher) to deliver cooling water before draining. 

Don’t forget to use fuel stabilizer when you fill your gas tank. Using fuel stabilizer is important because it prevents gasoline from oxidizing and leaving behind varnish-like deposits. The tank should be 95% full for winter storage. 

After treating the fuel and running the engine for a few minutes, the engine should be “fogged” with a storage lubricant. This protects the internals (bearings, seals, and rotating surfaces) with a thin film of lubricant, which helps keep rust and corrosion away. When the engine is running, inject fogging oil through the carburetors or electronic fuel injection system air intakes to flood the engine with oil. Continue fogging until the engine stalls. 

Finally, store your outboard engine in the trimmed down (running) position. Outboards are designed to drain all the water from their cooling systems completely when in this position. Remember, you don’t want any water in the engine over winter. 

Outboard Engine Winterization Checklist 

• • Fill installed fuel tanks and add stabilizer 

• • Flush engine with muffs and fresh water 

• • Turn off fuel supply and fog while running

• • Drain gear case and add fresh lubricant 

• • Store unit in lowest position 

• • Inspect/replace anodes 

Don’t forget, personal watercraft (PWC) need to be winterized, too! 

Once you've completed your boat winterization, you can relax and go back to dreaming about next summer on the lake.

Marine Accessories 

Marine Fuel Tanks