How Long Can You Leave Gas In A Boat? Boat Gas Lifespan?

Many people don’t realize that the gasoline you put in your boat or jet ski will go bad, and often quicker than most think.

For most people, they refill their cars every week or two, so the thought of gas going bad is not an issue. Also, boats work in a very different environment than a car, so different things need to be considered, especially if you get your gas from the same place you get the gas for your car.

How Long Can You Let Gas Sit In A Boat?

Gas in a boat can start to go bad as soon as 1 month to 6 months, depending on how it’s stored and what gas you used.

If the gas contains ethanol, which most gas from a gas station contain, then it starts to go bad after 1 month and will be useless after a few more months. Ethanol gas loves water and since boats operate in such a wet environment, the gas in them can go bad quickly.

For boats that are not supercharged or have complex computer systems, they will not notice the gas starting to go bad for longer than if your boat did have such things. In other words, if you have a little John-Boat, then it will be less picky than a 300HP boat.

How To Keep Boat Gas From Going Bad?

To keep the gas in your boat from going bad, you need to add some fuel stabilizer to it.

The best kind of fuel stabilizer are the ones made for boats like this one here. (Amazon Link Ad)

Using the correct fuel stabilizer can keep your boat’s gas fresh for 12 months. It’s also ideal to use the marine stabilizer, as the environment for a boat is different from your car or similar stabilizer.

How Often Should You Add Fuel Stabilizer To Your Boat?

If you ride your boat every week or two, adding fuel stabilizer is not needed.

But adding fuel stabilizer after every fill up of your boat is cheap insurance.

The marine stabilizers do more than keep the gas fresh, it helps to pick up where ethanol wreaks havoc. Boat engines take a lot more abuse than your car engines and tend to be more picky about the fuel they use. Adding stabilizer to every fill up or every other one can help keep the engine going at its best and buy you time if you don’t drive your boat for a month or more.

How Much Gas Should You Leave In A Boat Over The Winter?

How much gas you leave in your boat is a hotly debated topic.

On one side, you have people who think you should leave the gas tank nearly full when storing the boat. The reason to keep it nearly full is that the more gas you have in the tank, the less water can come in the tank.

The other side thinks you should leave the gas tank nearly empty, one or two bars. The less gas you have, the less water will mix with it and will be “diluted” out when you fill the tank backup at the start of the season.

It’s all opinion, but I’m of the camp to leave the tank nearly empty when storing my boat.

Gas is expensive and if it does go bad, I rather replace a few gallons than a full tank. It’s easier to put 90% fresh gas in, then take out 100% of the bad gas when the season starts. Also, storing that a full tank of gas can be dangerous and a target for thieves.

I would still run some fuel stabilizer through the engine and lines, just so that the gas that sits in the engine doesn’t go bad or gum up.

Why Does Gas In Boats Go Bad?

Gasoline goes bad in general, but most never notice it because they’re always filling up their cars every week or two before the gas goes bad.

Also, cars and trucks tend to be less picky about the gas. Your car may have a year-old gas, but it quickly adjusts to the octane it’s at because cars are not stressed like a boat. For most boaters, especially jet skis, they’re either at idle or near full throttle. Cars also have transmissions to keep the engine from working as hard, while boats don’t, so they tend to be run harder.

A boat or jet ski will quickly throw a check engine light when the gas is not at the level it needs.

Then you also have the very wet environment that boats operate in. Ethanol doesn’t attract water, unlike what most people think, but it does love water and condensation will find its way into the gas tank and will mix very well with the ethanol gas in your boat. It’s this love for water that makes ethanol gas so bad for boats, and it’s the type of gas that most gas stations sell.

One important thing to consider is that the gas tank in your boat is larger than one in your car or truck. A little water in your car’s 10 gallon gas tank is not as noticeable as the same amount of water in your boat’s 50+ gallon gas tank. When you fill up at the gas pump, you take more of the gas and thus stir up more of the crap at the gas station. Boats tend to end up with more water and gunk than many cars or truck miss due to boat needing more.

Warning Signs Of Bad Gas?

The most obvious warning sign of bad gas is a boat that won’t start or runs rough.

Another sign the gas is bad is a check engine light on your boat or jet ski, this is more common on supercharged engines.

Most of the time when you give the engine a load is where the signs of bad gas become most obvious. So, you may not notice the problem until you go out and drive the boat, revving the engine at the dock is not always a good indicator that everything is working fine.

If the gas is bad, the best thing to do is get rid of it. If you don’t know what you’re doing, it’s best to let the boat repair shop do it for you. The gas may not be good for your boat, but will be fine for lawn mowers and in some cars mixing half of it with fresh gas is fine. About half the time, the gas is so bad that it’s not worth it even for a lawn mower, so your experience may vary.

Will Bad Gas Damage Boat Engines?

Bad gas can damage an engine, but not in the way many people think.

It’s the water that gets into the gas that causes all the problem. When it comes to water, it freezes and expands, which will damage parts of the engine that can’t stand the expansion.

Also, old gas can cause a motor to have pre-detonation and break/burn pistons.

Then you have the gummy substance that is left behind when gas goes bad and causes lines to get clogged and parts to stop working.

In general, bad gas is not good for engines.