Video: Winterizing Your Outboard: Fuel-System Storage Tips


When it comes to storing your gasoline engine—whether it’s an inboard, outboard or I/O—for long periods, preserving the fuel and protecting the engine’s internal components from moisture and corrosion are the main considerations. Before you take on the pre-storage job, however, be aware that different manufacturers have different winterizing requirements, so consult your engine manufacturer, dealer or engine manual beforehand to avoid damaging the engine or voiding the warranty. Also, note that the storage procedure described in this article and the accompanying video may not be right for your particular make, model and type of engine. For example, 4-stroke, 2-stroke, DFI and carburetor-equipped engines all have different storage and maintenance requirements.

Again, the basic goals of winterizing an engine are (1) preventing internal and external corrosion of metal parts and (2) stabilizing the fuel to prevent the formation of varnish, gum and deposits in the fuel system during periods of non-use.

The first step when it comes to winterizing my 2004 200-hp Mercury OptiMax DFI outboard is to drain as much existing fuel from the engine as possible then run a fuel stabilizer and conditioner mix through the fuel system to prevent the formation of gum or varnish during layup. Here’s what my engine manual recommends:


  1. Remove the internal fuel filter from the engine’s vapor separator. This filter should be changed at least once a year, according to Mercury. (By the way, this task is made infinitely easier if you purchase a filter-removal attachment that fits the castellations on the filter head and can be used with a socket wrench.)
  2. Detach the hose from the drain fitting on the right side of the vapor separator, loosen the drain screw to the filter chamber (located on the left side of the fuel chamber) and allow fuel to drain from the filter chamber into a container.
  3. Once the fuel has drained, tighten the drain screw and reattach the hose to the right-side drain fitting.
  4. Next, remove the hose from the left fitting, loosen the drain screw on the right side of the vapor separator and allow the fuel to drain.
  5. When all the fuel has drained, tighten the right drain screw and reattach the hose to the fitting.
  6. Now pour 4 ounces of premixed fuel stabilizer and fuel conditioner directly into the filter chamber.
  7. Install a fresh fuel filter and replace the engine cowling.
  8. The next step is to run stabilized fuel through the engine. While you can run the engine off the main tank if you’ve already treated the fuel, I like to make up a small, separate container of fresh treated fuel and run the engine off that source.
  9. Add the recommended amount of fuel stabilizer and fuel conditioner to 5 gallons of fresh gasoline, then attach the portable tank directly to the fuel hose on the engine. Start the engine and let it run for 5 minutes (after attaching a cooling-water hose, of course), allowing the treated gas to circulate through the system.
  10. After 5 minutes, detach the fuel line from the portable tank and reattach it to the main tank.
  11. Bonus tip: As for the gas in the main tank, if you can’t drain it completely before the end of the season, keep it topped off and treat it with the appropriate amount of stabilizer, conditioner and ethanol treatment. Just be sure to leave some space for expansion of due to changing temperatures; otherwise, you could damage the fuel lines or tank.

Do you know of other engine-storage tips?

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