How Long Before Boat Fuel Goes Bad?

For a boat equipped with an internal combustion engine, fuel obviously starts to run out as you operate the boat. However, that same fuel can go bad if you let it sit in the tank long enough. 

How long until boat fuel goes bad

Bad gasoline can gum up fuel system components, damage the engine and degrade performance. So it’s important to either go boating enough to keep burning through the gasoline you have in the fuel tank before it goes bad, or take measures to make sure you’re not left with a batch of bad fuel.

Buy Mercury Quickstore fuel stabilizer

Buy boat fuel filters

How Long Will Fuel Last in a Boat?

Gasoline less than a couple of months old is generally going to be okay, but if you’re storing your boat longer than that, there are ways to extend the fuel’s viability. Fuel stabilizer helps slow down the oxidation process and break down water in the fuel. 

Boat fuel stabilizer

Depending on the stabilizer you buy, it can also help prevent ice buildup in your boat engine’s fuel system. Our video below shows you how to winterize an outboard and use stabilizer. It’s important to run the engine for a bit after you add the stabilizer to circulate it into the fuel system.

What Will Old Gas Do to an Engine During the Winter?

One issue with stored gasoline is that it’s often not just fuel. Water suspended in gasoline can separate out and freeze inside lines. If enough of it does, it’ll damage fuel system components.

How long before boat gasoline goes bad fuel line

Storing your boat in a warmer environment can help. One way to prevent condensation from happening is to fill the tank more than half-full during the winter, since this can help reduce the contraction of the fuel.

How Do You Know Boat Gasoline Has Gone Bad?

The smell is the first clue. Bad gasoline has a sour smell, and looks darker than fresh fuel. You’ll also notice it when you try to start and run the engine. It may be tough to start, and it’ll run rough when it does. 

Bad fuel and fuel system problems are possible reasons an outboard motor is having idling problems or won't idle at all. Watch the video above to learn more about how bad fuel and other issues can cause outboard engine idling problems




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