Is It Bad to Put Ethanol in Your Car?

Generally, it’s not bad to use ethanol-blended gasoline in your car—as long as you use the blend your vehicle is designed for. Most modern cars are built to run on E10 (10% ethanol), many 2001-and-newer U.S. vehicles can use E15 (15% ethanol) where allowed, and only flex-fuel vehicles (FFVs) should use E85 (up to 85% ethanol). Using a higher-ethanol blend than your car is rated for can cause drivability issues, potential component wear, and may void warranties, while all ethanol blends will slightly reduce fuel economy.

What “putting ethanol in your car” really means

At the pump, you’re not choosing pure ethanol; you’re choosing a gasoline-ethanol blend with a stated percentage. Understanding the common blends and compatibility will help you choose correctly and avoid problems.

• E0: 0% ethanol gasoline. Often labeled “ethanol-free” or “recreational fuel.” Maximizes fuel economy and is favored for storage and small engines, but may be pricier and less available.
• E5/E10: 5–10% ethanol. Standard in many countries; safe for virtually all modern gasoline cars. Expect about 2–4% lower MPG versus E0.
• E15: 15% ethanol. U.S. EPA-approved for 2001-and-newer light-duty gasoline vehicles; not for motorcycles, heavy-duty, marine, or small engines. Availability varies by region and season. Typical MPG drop ~4–5% versus E0.
• E85: 51–85% ethanol (varies seasonally). Only for flex-fuel vehicles (FFVs). Higher octane can benefit engines calibrated for it, but expect 25–30% lower MPG versus E0.

In practice, choosing the right blend is about matching your vehicle’s certification to the pump label: use what your manual and fuel-door sticker allow, and don’t go higher.

Potential benefits of ethanol blends

Ethanol isn’t just a filler; it adds properties that can be advantageous in the right context. These are the upsides drivers are most likely to notice or value.

• Higher octane: Ethanol boosts octane, which can reduce knock; E85 has very high octane (roughly mid-90s AKI), enabling more aggressive tuning in FFVs and performance builds.
• Cleaner combustion: As an oxygenate, ethanol can reduce carbon monoxide and certain aromatics compared with straight gasoline.
• Widespread availability: E10 is the default in many markets; E15 access is growing in parts of the U.S.
• Cost dynamics: Depending on local pricing and incentives, higher-ethanol fuels can be cheaper per gallon (though not always per mile due to lower energy content).

These benefits make ethanol blends a practical, everyday choice for most drivers and a performance tool for properly calibrated engines.

Risks and when ethanol can be “bad” for your car

Problems arise primarily when the ethanol percentage exceeds what your vehicle was designed to use, or when the car sits for extended periods. Here’s what to watch for.

• Wrong blend for the vehicle: Non-FFVs using E85 (or older vehicles not approved for E15) can see hard starts, rough running, lean conditions, or check-engine lights; warranty claims may be denied.
• Fuel system compatibility: Older cars (especially pre-2000) may have seals, hoses, and fuel-system components not designed for higher alcohol content, risking swelling, cracking, or corrosion.
• Lower fuel economy: Ethanol contains less energy per gallon; expect modest MPG loss with E10/E15 and significant loss with E85.
• Storage and moisture: Ethanol is hygroscopic. In vehicles that sit for months, absorbed water can lead to phase separation and corrosion; small engines and marine systems are especially vulnerable.
• Cold-weather starts: High-ethanol blends can be harder to ignite in low temperatures; FFVs compensate with calibration and seasonal fuel adjustments.
• Non-road engines: Motorcycles, boats, lawn equipment, and generators often aren’t approved for E15 and may run poorly even on E10; consult device-specific guidance.

Used appropriately, ethanol is routine and low-risk; misused, it can create avoidable drivability and maintenance headaches.

How to know what your car can safely use

Compatibility isn’t guesswork. You can verify ethanol limits quickly with these sources and cues.

• Fuel-door sticker and owner’s manual: The definitive guidance for your make, model, and year.
• Model-year rules of thumb (U.S.): EPA approves E15 for 2001+ light-duty gasoline vehicles; E85 is only for FFVs. Many automakers explicitly allow E15 on later-model cars—check the manual for confirmation.
• Badging and VIN: FFVs often have yellow fuel caps, “Flex Fuel/E85” badges, or VIN identifiers indicating E85 capability.
• Official checkers: Government or manufacturer compatibility tools exist in several countries (e.g., U.S. DOE’s AFDC, the UK’s E10 vehicle checker).
• Warranty statements: If the manual or OEM bulletin doesn’t list E15/E85, assume it’s not covered.

When in doubt, follow the most conservative official source for your vehicle to avoid performance issues and protect your warranty.

Regional and regulatory notes (2025)

Fuel labeling and seasonal availability vary. In the U.S., E10 is ubiquitous, and E15 is growing. Beginning in 2025, the EPA finalized year-round E15 sales in several Midwestern states at state request; elsewhere, summertime E15 sales can depend on seasonal volatility rules or temporary waivers. Always check local pump labels and regulations.

In Europe and the UK, E10 has become the standard “regular” grade in many countries, with E5 commonly sold as a premium/super alternative for older or incompatible vehicles. If you drive an older or classic car, verify compatibility before using E10.

Best practices for using ethanol-blended fuel

A few simple habits can maximize benefits and minimize downsides when running ethanol blends.

• Use the blend your car specifies; don’t “up-blend” beyond the rating.
• Expect small MPG differences and track your fuel economy to compare per-mile cost.
• For seasonal or long-term storage, use ethanol-free fuel if available or add a quality stabilizer; keep tanks reasonably full to limit moisture.
• If you have an FFV and switch to E85, anticipate more frequent fill-ups; monitor for any drivability changes.
• Buy from reputable stations and consider Top Tier detergency for cleaner injectors and intake valves.
• If a check-engine light appears after a fuel change, revert to the approved blend and have the codes scanned.

Following these steps helps ensure reliable operation whether you use E10 daily, occasionally fill with E15, or run E85 in a flex-fuel vehicle.

Summary

It isn’t inherently bad to put ethanol in your car—most modern vehicles are designed for E10, many can use E15, and flex-fuel models can run E85. Problems arise when the ethanol percentage exceeds your car’s rating or when the vehicle sits unused for long periods. Expect modest MPG trade-offs, check your manual and fuel-door labels, and follow local regulations. Used as intended, ethanol-blended gasoline is a safe, common, and effective fuel for everyday driving.

Does ethanol damage car engines?

Ethanol can damage older car engines not designed to handle it, but generally does not harm newer vehicles. Ethanol can degrade rubber and plastic fuel system components, cause corrosion, and absorb water, potentially leading to fuel leaks, blockages, and engine problems in older cars and equipment like lawnmowers. Modern cars are built with ethanol-resistant parts and are typically safe to use with ethanol blends like E10 or E15.
 
Why ethanol can be damaging

• Material degradation: Ethanol is a solvent that can dissolve and degrade rubber, plastic, and cork components found in the fuel systems of older vehicles. 
• Corrosion: Ethanol attracts water, forming a corrosive mixture that can attack metal components in the fuel system, such as those in carburetors. 
• Water contamination: Ethanol is hygroscopic, meaning it absorbs water from the environment. If enough water is absorbed, it can cause the fuel to separate from the gasoline, creating a layer of water and ethanol that can damage engine components and cause performance issues. 
• Deposit removal: The solvent properties of ethanol can loosen deposits within the fuel system, which can then lead to blockages in fuel lines, filters, or injectors. 

Who is affected and why

• Older vehicles: Opens in new tabEngines and fuel systems manufactured before 1994 often contained materials that were not resistant to ethanol. 
• Small engines: Opens in new tabMany smaller engines in devices like chainsaws and lawnmowers also lack ethanol-resistant parts and may not tolerate ethanol blends, especially E10. 
• Marine motors: Opens in new tabEthanol and the higher water content in its operating environment do not mix well, posing risks to marine motors. 

Modern vehicles vs. older vehicles

• Modern vehicles (post-1994): Opens in new tabMost vehicles made from 1994 onward are designed with ethanol-resistant materials and can handle ethanol blends like E10 or E15. 
• Older vehicles: Opens in new tabFor older or “classic” cars, it is crucial to check the owner’s manual or factory service manual to determine if they are compatible with ethanol-blended fuels. 

What to do

• Check your owner’s manual: Determine if your vehicle is approved for a particular ethanol blend. 
• Consider fuel additives: Some additives are designed to help mitigate the effects of ethanol on older systems. 
• Use ethanol-free gasoline: For older engines or sensitive equipment, using ethanol-free gasoline can prevent damage. 

Does ethanol damage fuel lines?

Yes, ethanol can damage fuel lines, particularly in older vehicles and small engines, because its acidic and solvent properties can corrode and deteriorate non-ethanol-resistant materials like rubber and certain plastics. The risk is higher with higher ethanol concentrations and in vehicles manufactured before 2012, as modern fuel systems are built with ethanol-resistant components like stainless steel and special polymers.
 
How Ethanol Causes Damage

• Corrosion: Ethanol is mildly acidic and absorbs water from the atmosphere, which accelerates corrosion in metal components, especially steel and iron alloys. 
• Deterioration: As a solvent, ethanol can dissolve certain plastics and rubber, causing them to break down, crack, or become gummy. 
• Deposits: The dissolved material from corroded fuel system components can create deposits that clog filters, fuel injectors, and other critical parts. 

Factors Increasing Risk

• Age of the vehicle: Opens in new tabOlder vehicles and small engines, especially those manufactured before 1993 or the early 2000s, often have fuel systems that are not resistant to ethanol. 
• Ethanol concentration: Opens in new tabHigher ethanol blends, such as E85, can accelerate damage compared to lower blends like E10 (10% ethanol). 
• Moisture: Opens in new tabThe combination of ethanol with water can form a corrosive mixture, especially if it separates from the gasoline in the fuel tank. 

What You Can Do

• Inspect fuel lines: Opens in new tabCheck your fuel lines for signs of cracking, softening, or other deterioration during routine maintenance. 
• Use ethanol-resistant components: Opens in new tabWhen replacing fuel system parts, ensure they are made from ethanol-resistant materials, such as stainless steel or specific polymers. 
• Consider fuel treatments: Opens in new tabUse a fuel treatment like Biobor Fuel Additives to help keep the ethanol and gasoline in suspension, preventing phase separation and reducing the risk of corrosion. 
• Use ethanol-free gas: Opens in new tabFor older or sensitive small engines, using ethanol-free gasoline can be a good way to prevent damage. 

Is ethanol safe to put in my car?

Most vehicles manufactured in recent years are designed to handle ethanol blends up to E15 without significant issues. However, owners of older vehicles should be cautious and consider using fuel additives or avoiding high-ethanol blends to mitigate potential risks.

What cars should not use ethanol gas?

The EPA says E15 can be used in flexible-fuel vehicles, as well as 2001 and newer cars, light-duty trucks, and medium-duty SUVs. Don’t use E15 in motorcycles or other small engines, heavy-duty trucks, or nonroad vehicles such as boats and snowmobiles.