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Why Fuel Deteriorates – and How Gasoline Stabilizer Has Your Back

Brad Nelson
AMSOIL Gasoline Stabilizer is poured into a gas can to protect the fuel from oxidation during storage.

If you’ve ever pulled a lawn mower, snowblower, motorcycle or classic car out of storage only to discover it won’t start, there’s a good chance deteriorated fuel was to blame. Many of us have learned the importance of fuel stabilization the hard way after spending hours pulling on a rope or troubleshooting an engine that ran perfectly when we put it away for the season. Even those who know they should add a fuel stabilizer before seasonal storage often fail to follow through with the act. That might be because they do not understand why gasoline degrades in the first place, how fuel stabilizer helps prevent it or how easy and effective it can be.

Time Is the Enemy

Gasoline is a complex blend of hydrocarbons, energy-rich compounds made primarily of carbon and hydrogen atoms. It’s refined from crude oil through a distillation process that separates various petroleum fractions. Compared to diesel fuel and lubricating oils, gasoline contains lighter, more volatile hydrocarbons. Modern gasoline also typically contains ethanol, usually at concentrations of around 10%, though some fuels contain significantly more.

Just about everything degrades over time; gasoline does so rapidly. In fact, gas can begin to degrade in as little as 30 days under the right conditions. Exposure to heat, oxygen, humidity and atmospheric conditions gradually alters gasoline’s composition. As it ages, it forms gums, varnish and other deposits that can accumulate throughout the fuel system. These deposits restrict fuel flow, foul carburetors and injectors and make starting more difficult or even impossible. Old gasoline can change so significantly that it loses its ability to ignite properly. The result is a fuel that becomes less stable and effective over time.

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Why Fuel Breaks Down

Oxidation is one reason gasoline deteriorates so quickly. As it sits, oxygen reacts with gasoline molecules, creating varnish, gum deposits and other unwanted byproducts. At the same time, lighter hydrocarbons evaporate, concentrating the heavier compounds that contribute to deposit formation.

Ethanol introduces another challenge. Ethanol is hygroscopic, meaning it naturally attracts and absorbs moisture from the atmosphere. If enough water accumulates, phase separation can occur, a condition in which the ethanol and water settle apart from the gasoline. Once phase separation takes place, fuel quality drops dramatically, increasing the likelihood of fuel-system problems and hard starting. In addition, the presence of water in the fuel system can accelerate corrosion inside the engine, drastically reducing engine performance and longevity.

Proper storage can slow the process. Using high-quality gasoline and storing it in approved, airtight containers helps minimize exposure to air and moisture. Storing fuel inside a ventilated garage or shed is generally preferable to leaving containers exposed to the elements. But often that is not enough.

Stabilizer chemistry helps interrupt the oxidation process that causes gasoline to form gums and varnish, slowing the degradation that occurs during storage. By reducing these harmful reactions, a fuel stabilizer helps preserve fuel quality and maintain engine cleanliness.

8X Longer Fuel Stability

According to independent testing, AMSOIL Gasoline Stabilizer (AST) delivers strong protection against the oxidation processes responsible for gum and varnish formation. It also helps guard against corrosion during storage, an important benefit for maintaining fuel-system cleanliness and reliability. When added before storage, AMSOIL Gasoline Stabilizer helps preserve fuel quality for up to 12 months, reducing the likelihood of stale fuel, difficult starts and deposit-related issues when equipment is returned to service.

How good is it? As the graph below shows, AMSOIL Gasoline Stabilizer delivers eight-times longer fuel stability than Sea Foam* Motor Treatment in the triple-length gasoline oxidation stability test (ASTM D525), helping maintain startability and protect against the formation of varnish and gum.1

AMSOIL Gasoline Stabilizer also helps guard against corrosion during storage, an important benefit for maintaining fuel-system cleanliness and reliability. In fact, AMSOIL Gasoline Stabilizer provides corrosion protection Sea Foam Motor Treatment can’t match, helping maintain power and performance and keeping metal corrosion free, even when subjected to salt water.2

For shorter storage intervals of up to six months, AMSOIL Quickshot® (AQS) provides another solution. In addition to stabilizing fuel, it contains detergent and solvency-enhancing chemistry designed to help break down existing varnish and improve fuel-system cleanliness, making it a useful option for maintaining equipment that may already have some fuel-related deposits.

Dependable Power

Fuel deterioration is a natural consequence of time, oxygen exposure and ethanol-related moisture absorption. Left untreated, aging gasoline can form deposits, cause corrosion and create starting problems that turn seasonal equipment maintenance into a frustrating and potentially expensive chore. Adding AMSOIL Gasoline Stabilizer before storage helps slow oxidation, preserve gasoline quality and protect critical fuel-system components. Whether you’re storing a lawn mower for the winter, parking a motorcycle for the season or keeping fuel on hand for outdoor power equipment, fuel stabilization remains one of the simplest and most effective ways to ensure dependable starts when it’s time to get back to work or play.

Video transcript: How to Get your Lawnmower Ready for Storage

Welcome to Tech Tips. I’m Len Groom, Technical Product Manager for Powersports. A lot of people ask me, What do I need to do to put my lawnmower in storage? Well, here’s a few tips that will help to ensure that your lawnmower will start up when you get it out of the shed in the spring.

The first and probably the most important thing to do would be to change the oil. Contaminants can build up from combustion, from use, from dust and dirt in the environment, and they can end up in the oil. So it’s always good to put the mower in storage with fresh oil in it. Changing the oil isn’t that tough.

Here’s how you do it. The first thing you need to do is drain the oil out. So you want to locate the plug which is underneath, remove it and drain the oil into a pan. You want to add the appropriate amount of oil until the dipstick registers full.

I recommend AMSOIL’s Formula 4-Stroke Small Engine Oil in 10W-30 for this application. Next, you want to treat the fuel. No matter what type of fuel you’re using, you always want to treat it. AMSOIL has two different options.

The first one would be AMSOIL’s Gasoline Stabilizer. This one is designed for long-term storage. This will help fight all forms of fuel deterioration from corrosion to varnish to any type of buildup. This is for long-term.

The second option would be AMSOIL’s Quickshot. This is designed to be used over the course of the summer. This will also help fight corrosion. It will help fight any type deterioration.

But this product also helps with any of the issues that are associated with ethanol. So, one way or the other, make sure you’re treating your fuel. Next, let’s take a look at the air filter. It’s often overlooked.

It’s usually pretty easy to get to. So you want to take the cover off, inspect it, clean it if you can. But, if it’s too dirty, replace it. So there you have it.

Just a few simple things that you can do to ensure that your mower comes out of storage ready to run. One thing we should note: If you ever have a question on quantity or any of these procedures, the first thing you should do is consult your owner’s manual. One last thing: Some of these new lawnmowers, specifically the push mowers, don’t have a drain plug. So you need to look in your owner’s manual for the procedure.

Most of the time it’s going to want you to drain the oil out through the filler neck. Thanks for watching. We’ll see you next time.

1Based on independent third-party testing of AMSOIL Gasoline Stabilizer obtained July 1, 2022 and Sea Foam Motor Treatment purchased June 30, 2022 in a triple-length gasoline oxidation stability test (ASTM D525) using test fuel containing no oxidation-stability-improving additives. 2Based on independent third-party testing of AMSOIL Gasoline Stabilizer obtained July 1, 2022, and Sea Foam Motor Treatment purchased June 30, 2022, in a modified NACE TM0172 using synthetic sea water per ASTM D665B.