How Ethanol Fuel Damages Small Engines

Ethanol-blended gasoline is widely available, but it’s one of the biggest causes of small engine problems. If you work on lawn mowers, snow blowers, chainsaws, generators, or other outdoor power equipment, you’ve likely seen the damage firsthand. Understanding how ethanol fuel damages small engines can help you prevent costly repairs and extend engine life.

In this guide, we’ll break down what ethanol fuel is, why it’s harmful, common symptoms of ethanol damage, and how to protect your equipment. This blog contains affiliate links for your convenience. We may make a small commission from purchases at no extra cost to you.

What Is Ethanol Fuel?

Ethanol fuel is gasoline blended with alcohol, typically E10 (10% ethanol). While ethanol works in modern vehicles, it causes serious problems in small engines that are not designed to handle alcohol-based fuels.

Most small engine manufacturers warn against long-term use of ethanol fuel, especially in equipment that sits unused for months.

Why Ethanol Is Bad for Small Engines

1. Ethanol Attracts Moisture

Ethanol is hygroscopic, meaning it absorbs water from the air. When moisture enters the fuel system, it causes:

Rust inside fuel tanks

Corrosion in carburetors

Poor combustion

Hard starting or no-start conditions

Water-contaminated fuel is a leading reason small engines won’t start after storage.

2. Ethanol Causes Carburetor Clogging

As ethanol fuel sits, it breaks down and leaves behind varnish and gum deposits.

These deposits:

Plug carburetor jets

Stick float needles

Restrict fuel flow

A dirty carburetor is one of the most common small engine repair issues caused by ethanol fuel.

3. Ethanol Deteriorates Rubber and Plastic Parts

Alcohol-based fuels attack rubber fuel lines, primer bulbs, gaskets, and O-rings.

Over time, ethanol fuel can cause:

Cracked fuel lines

Swollen seals

Fuel leaks

Air leaks leading to lean running

These issues often result in engine surging, stalling, or loss of power.

4. Phase Separation Damages Engines

When ethanol absorbs too much moisture, phase separation occurs. The ethanol and water separate from the gasoline and settle at the bottom of the tank.

This leads to:

Engines running on water-heavy fuel

Severe corrosion in the carburetor

Engine failure during startup

Once phase separation happens, the fuel is no longer usable.

5. Lean Running and Engine Overheating

Ethanol burns differently than pure gasoline. In small engines, it can cause:

Lean air-fuel mixtures

Higher engine temperatures

Valve damage

Piston scoring

Long-term ethanol use increases the risk of internal engine damage.

Symptoms of Ethanol Fuel Damage in Small Engines

Watch for these warning signs:

Small engine won’t start

Engine starts then dies

Hard starting after storage

Engine surging or hunting

Fuel leaks or cracked fuel lines

Rough idle or poor performance

If you see these symptoms, ethanol fuel may be the culprit.

Equipment Most Affected by Ethanol Fuel

Ethanol causes the most damage to equipment that sits unused:

Lawn mowers

Snow blowers

Chainsaws

Weed eaters

Leaf blowers

Pressure washers

Portable generators

Seasonal equipment is especially vulnerable.

How to Prevent Ethanol Fuel Damage

Use Ethanol-Free Fuel

Whenever possible, use ethanol-free gasoline. Many gas stations sell non-ethanol (recreational) fuel for small engines or you can buy canned ethanol-free fuel with small engine additives here.

Add Fuel Stabilizer. Get it here.

Fuel stabilizers slow fuel breakdown and help prevent moisture absorption.

Add stabilizer to fresh fuel

Run engine to circulate treated fuel

Drain Fuel Before Storage

Before long-term storage:

Shut off fuel valve

Run engine until it stalls

This prevents varnish buildup and corrosion.

Replace Fuel System Parts When Needed

If fuel lines or primer bulbs feel soft, brittle, or cracked, replace them with ethanol-resistant parts.

Have carburetor cleaned or replaced as needed. Buy carb cleaner here.

Is Ethanol Fuel Ever Safe for Small Engines?

Short-term use of E10 fuel may be unavoidable, but it should never sit in a small engine for extended periods. The longer ethanol fuel sits, the more damage it causes.

For best results:

Use ethanol-free fuel

Store equipment properly

Perform regular maintenance

Final Thoughts

Ethanol fuel may be common, but it’s one of the top causes of small engine failure. From clogged carburetors to fuel system corrosion, understanding how ethanol fuel damages small engines helps you avoid expensive repairs and downtime.

Preventative maintenance and proper fuel choices can keep your equipment running reliably for years.