Explained: Harmful effects of ethanol-blended fuel with real examples

Many older vehicles, even as recent as BS-IV models, were never designed to deal with ethanol’s corrosive nature

BHPian The_Artificer recently shared this with other enthusiasts:

Hello Fellow BHPians,

This thread is entirely about ethanol blended fuel and it's effect on older vehicles, say the ones without an EFI ( Electronic Fuel Injector) and the pre 2018 era. And even newer E20 compatable ones with poor maintenance. And thank you in advance for your time to read this long thread.

Chapter 1 – The Green Push, But at What Cost?

India has been steadily marching toward a greener automotive future. One of the major steps in this journey is the introduction of ethanol-blended fuels, which aims to reduce dependency on fossil fuels and cut down carbon emissions. Alongside this, the evolution of emission norms in India has also been rapid and aggressive.

To give a quick timeline for context, the Bharat Stage (BS) emission norms were introduced in 2000 (termed India 2000), essentially mirroring Euro 1 standards. Over the years, we moved through BS-II and BS-III with reasonable transition periods. By 2017, BS-IV was implemented nationwide. Then came the ambitious leap, skipping BS-V altogether, India jumped directly to BS-VI in 2020, bringing in drastically reduced emission limits and tighter vehicle compliance requirements.

On paper, this sounds like progress. And indeed, it is, for the environment.

However, every big change brings its set of unintended consequences.

One such ripple effect has been the growing adoption of ethanol-blended fuels, particularly E10 and E20 blends (10% and 20% ethanol, respectively). While these fuels promise cleaner combustion and reduced oil import bills, their compatibility with existing vehicle infrastructure, especially older machines is questionable.

Many older vehicles, even as recent as BS-IV models, were never designed to deal with ethanol’s corrosive nature, its tendency to absorb moisture, and its lower energy density compared to pure petrol. This has led to issues ranging from fuel system degradation to starting troubles, especially in regions where E20 fuel is already being sold.

Even modern E20-compliant vehicles aren’t completely immune. While manufacturers have upgraded components like fuel lines and injectors, several real-world cases and mechanic reports point toward accelerated wear, particularly in two-wheelers that are used irregularly or are left parked in the sun.

So while the green intent is undeniable and commendable, there’s a mechanical reality to acknowledge, ethanol-blended fuels are not entirely kind to machines that weren't built with it in mind.

Chapter 2 – The Chemistry of Ethanol-Blended Fuels and Their Effects on Engines

Ethanol (C₂H₅OH) is an alcohol-based compound derived from biomass ( Either sugarcane or other similar derivatives). While it is renewable and burns cleaner than pure gasoline, its chemical and physical properties introduce several challenges when blended with petrol.

1. Hygroscopic Nature

Ethanol is hygroscopic, meaning it readily absorbs moisture from the atmosphere. When blended with petrol, this can lead to phase separation, where water and ethanol settle at the bottom of the tank, leaving a stratified fuel mix. This can cause:

• Rusting of fuel tanks and lines (especially in older steel tanks).
• Incomplete combustion, misfires, and stalling.
• Fuel pump and injector wear due to contaminated fuel.

2. Corrosive Properties

Ethanol reacts with certain metals and rubber compounds. In older vehicles, parts like:

Carburetor floats, fuel lines, and seals and gaskets are often made from materials not resistant to ethanol. Over time, ethanol causes swelling, hardening, or cracking, resulting in leaks, loss of pressure, and inconsistent fuel delivery.

3. Lower Energy Density

Ethanol contains approximately 34% less energy per unit volume compared to petrol. This means,

• Reduced mileage (~3–5% drop in E10, and more in E20).
• Leaner air-fuel mixtures, unless the ECU compensates, something not possible in older, non-EFI vehicles.
• Increased engine temperatures and potential for knock if ignition timing isn’t adjusted.

4. Volatility and Cold Starts

Ethanol has a higher heat of vaporization than petrol, making cold starts harder, especially in carbureted engines. In monsoon-prone or cooler regions, this results in:

• Longer cranking times,
• Frequent use of choke,
• And even carbon buildup due to incomplete warm-up cycles.

While ethanol is eco-friendly on paper, its chemical behavior inside the fuel system is anything but friendly to vehicles not specifically designed for it.

Chapter 3 – Case Studies

While the science of ethanol blending lays the foundation for understanding the risks, real-world experiences bring that theory into sharper focus. Below are three documented case studies from owners who faced issues, ranging from older 2-stroke legends to brand-new scooters that are technically E20 compatible.

Case Study 1: 1999 Yamaha RX 135 (5-Speed)

A close friend of mine, owns a recently restored Yamaha RX135. With careful running, Castrol Power 1 2T oil, and XP95 (which contains ~12% ethanol), the bike was performing flawlessly. One weekend, he loaned it to a friend, who unknowingly filled it up with E20 fuel and the brand less 2T oil available on a jug in most bunks outside the city. The bike sat for 4–5 rainy days in Chennai while its owner was away in Bengaluru.

Upon his return, the RX refused to start. After push-starting and a rough idle, they noticed fuel leaks near the petcock and a metallic smell from the tank.

Upon inspection, rusting had started inside the 1/4 full tank, with visible ethanol-water separation. The petcock’s rubber gasket was degrading.

That RX tank

He drained the tank, cleaned the carburettor, used Scottoiler FS365 Corrosion Protector,

and switched to XP100 fuel. Post-cleaning, the bike now runs smoothly, but the lesson was clear, older carbureted bikes weren’t built for high ethanol content.

Case Study 2: 2017 Honda Aviator BS4

This is my mom's scooter which is now my secondary vehicle.

Symptoms after E10/E20 became standard:

• Rough idling, especially on cold mornings.
• A strong petrol smell after shutdown.
• Drop in mileage and noticeably sluggish pickup.
• Repeated cold starts now require manual throttle blips, which was never the case earlier.

This scooter has no fuel injection, no knock sensor, and runs a simple CV carb setup, which makes it vulnerable to lean burn, fuel line swelling, and vapor lock.

Next step, I'm planning to fill it up with XP95 (with slightly lower ethanol content and higher RON) and monitor improvements, if any. A full carburettor cleaning is also on the checklist.

Case Study 3: 2024 Suzuki Avenis 125 (E20 Compatible)

My buddy owns a Suzuki Avenis 125, which is nearly a year old now, and though being E20 compatible on paper, he faced issues under real-world heat conditions.

His university parking has no shade at all and he was forced to park on the open sun throughout the summer season and that resulted in

• A strong fuel odor was present by evening.
• Cold starts became inconsistent, with slightly longer crank cycles.
• A crack formed on the breather pipe of the not too complicated EVAP (Evaporative Emission Control) system of the scooter, when compared to other bigger bikes with E20 compliance.

At the Suzuki 2 wheelers ASC, the mechanic mentioned that,

"Even the E20-ready Access 125s ( 2024) are reporting similar problems. The heat increases ethanol evaporation pressure, and the system wasn’t designed for these extremes."

This brings up a stark truth: ‘E20 compatibility’ doesn't guarantee real-world immunity.

So, What Can Owners Do?

Regardless of whether your ride is E0-only, E10-capable, or E20-compatible:

• Avoid leaving ethanol-blended fuel in the tank for weeks, especially in monsoon or humid climates.
• Fill tanks to at least ¾ capacity if parking for more than a few days. Less air space = less water absorption.
• Use XP95 or XP100 fuel (with less ethanol) when possible, especially for older machines.
• Keep fuel tanks rust-free by using rust protectants like Scottoiler or WD-40’s specialist range.
• For scooters, replace fuel lines and breather hoses every 1–2 years, especially in tropical heat.
• Consider parking under shade or using reflective covers to reduce ethanol volatility in summer.

Final verdict

Ethanol is the future, but we must bridge the gap between policy and real-world ownership. While it's commendable that manufacturers are rolling out E20-ready vehicles, millions of older vehicles still serve reliably in cities, villages, and mountains.

Educating ourselves and taking preventive steps will ensure these machines continue to live long, and run strong.

And Thank you for reading this long and

Ride Safe, Always wear your helmets and Happy Motorcycling!

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