Ethanol in Gasoline Causing Problems for Classic Cars

Modern gasoline contains ethanol—typically 10% (E10), but sometimes 15% (E15) or even 85% (E85). While ethanol burns cleaner and reduces dependence on petroleum, it creates serious problems for classic cars designed when gasoline meant pure petroleum. Understanding ethanol’s effects on vintage vehicles can save you thousands in repairs and keep your classic running reliably.

Why Ethanol Damages Classic Cars

Fuel System Corrosion

Ethanol is hygroscopic—it absorbs water from the air. When water enters your fuel system through ethanol absorption, it causes rapid corrosion of metal components. Classic car fuel systems use materials that simply weren’t designed to handle ethanol’s corrosive properties.

Steel fuel tanks, common in vintage cars, develop rust from the inside out when exposed to ethanol-water mixtures. The rust flakes contaminate fuel filters and carburetors. Fuel lines made from natural rubber and older synthetic rubber compounds deteriorate, becoming soft and eventually leaking. Zinc-plated fuel sending units corrode, leading to inaccurate fuel gauges.

Carburetor and Fuel Pump Problems

Ethanol dissolves deposits and residues that have built up in fuel systems over decades. While this sounds beneficial, these dissolved materials clog carburetor jets and fuel filters. The alcohol also attacks carburetor gaskets, accelerator pump diaphragms, and needle-and-seat assemblies made from cork, paper, and early synthetic materials.

Mechanical fuel pumps with rubber diaphragms fail when ethanol causes the rubber to swell, harden, or develop cracks. Electric fuel pumps from the 1960s-1980s often have internal components that ethanol damages.

Phase Separation: The Silent Killer

When ethanol-blended fuel absorbs enough water (just 0.5% water content), phase separation occurs. The ethanol and water separate from the gasoline and sink to the bottom of the tank as a distinct layer. This layer of ethanol-water mixture causes several catastrophic problems:

• The water-ethanol layer can’t burn efficiently, causing rough running, stalling, and no-start conditions
• Concentrated ethanol solution is even more corrosive than E10
• The octane rating of the remaining gasoline drops, potentially causing detonation and engine damage
• Fuel pumps draw from the bottom of the tank, meaning they’ll pull this contaminated mixture first

Phase separation happens surprisingly fast in vehicles that sit. A car stored for 3-6 months with E10 fuel can develop separated fuel, especially in humid climates or unheated storage.

Performance and Driveability Issues

Reduced Fuel Economy

Ethanol contains about 30% less energy per gallon than pure gasoline. Running E10 typically reduces fuel economy by 3-4% compared to pure gasoline. For a classic car that already gets 12-15 mpg, losing another 0.5-1 mpg adds up over time.

Lean Running Conditions

Ethanol changes the stoichiometric air-fuel ratio. Carburetors jetted for pure gasoline run lean when fed ethanol-blended fuel. This causes:

• Higher operating temperatures
• Hesitation and stumbling during acceleration
• Potential engine damage from running too lean
• Increased emissions

Some classic car owners re-jet carburetors for E10, but this creates problems if you ever find ethanol-free gas or travel to areas with different blend ratios.

Vapor Lock Susceptibility

Ethanol lowers the boiling point of gasoline and increases vapor pressure. Classic cars with fuel lines running near hot engine components are already prone to vapor lock. Ethanol makes this problem worse, causing stalling in traffic or after hot-soak conditions.

Solutions for Classic Car Owners

Use Ethanol-Free Gasoline

The ideal solution is to use only ethanol-free fuel in your classic car. Pure gasoline (sometimes called “recreational fuel” or “marine fuel”) is available at select stations. Use the website pure-gas.org to find ethanol-free stations near you.

Expect to pay $0.50-1.50 more per gallon for ethanol-free premium fuel. For a classic driven 2,000 miles annually averaging 12 mpg, that’s $80-250 extra per year—cheap insurance against fuel system damage.

If ethanol-free fuel isn’t available, use the highest octane E10 available (premium grade). Higher-grade fuels generally have more detergents and better-quality additives.

Upgrade Fuel System Components

Modern materials resist ethanol damage. Consider these upgrades:

Fuel lines: Replace rubber lines with modern ethanol-resistant fuel hose. Look for SAE J30 R9 or R10 rated hose specifically marked for ethanol use. This is a relatively inexpensive upgrade ($50-150) that prevents dangerous fuel leaks.

Carburetor rebuild kits: Use rebuild kits with ethanol-resistant materials. Viton O-rings, modern gasket materials, and updated accelerator pump diaphragms resist ethanol better than original components.

Fuel tank: If your tank shows rust damage, consider professional restoration with ethanol-resistant sealant, or replacement with a modern reproduction tank. Some companies offer fuel tanks with internal coatings designed for ethanol.

Fuel filter: Install a high-quality fuel filter and inspect it regularly. Ethanol-dissolved deposits will show up here before damaging your carburetor. Change filters more frequently than with pure gas—every 3,000-5,000 miles or annually.

Fuel Additives and Stabilizers

Several additives address ethanol-related issues:

Ethanol fuel stabilizers: Products like STA-BIL 360 Marine or Star Tron help prevent phase separation and corrosion. Use these if your classic sits for more than two weeks between drives. Follow dosage instructions carefully—more isn’t better.

Water absorbers: Additives that remove small amounts of water from fuel can help, but they’re not a solution for phase-separated fuel. If separation has occurred, drain and replace the fuel.

Corrosion inhibitors: Some additives claim to protect metal components from ethanol corrosion. These help but aren’t substitutes for physical component upgrades.

No additive makes E10 as safe as pure gasoline for long-term storage. They reduce but don’t eliminate ethanol-related problems.

Storage Practices

Proper storage minimizes ethanol damage:

Fill the tank before storage: A full tank reduces air space, limiting moisture absorption. This is particularly important if you must store with E10 fuel.

Add stabilizer before storage: Mix stabilizer with fresh fuel, then run the engine for 10 minutes to distribute treated fuel throughout the system.

Consider draining for long-term storage: If storing longer than 3-4 months, especially in humid conditions, some owners drain the fuel system completely rather than risk phase separation. Run the car until it stops from fuel starvation, ensuring carburetors and fuel lines are dry.

Start and drive periodically: If possible, start and drive your classic monthly. This circulates fuel, prevents settling, and maintains seal lubrication.

Symptoms of Ethanol Damage

Watch for these warning signs:

• Difficulty starting, especially when hot
• Rough idle or stalling
• Hesitation or flat spots during acceleration
• Fuel odor inside the car (indicating leaking lines)
• Visible fuel leaks, especially at rubber hose connections
• Rust-contaminated fuel filter
• Erratic fuel gauge readings

If you experience several of these symptoms, inspect your fuel system thoroughly. Catching problems early prevents being stranded and limits repair costs.

The Long-Term Outlook

Ethanol in gasoline isn’t going away. Federal mandates require it, and E15 may become more common. Classic car owners must adapt through component upgrades, careful fuel selection, and proper storage practices.

The good news: awareness is growing. Manufacturers now offer ethanol-compatible replacement parts for popular classics. More gas stations are maintaining ethanol-free fuel pumps. Advocacy groups like SEMA (Specialty Equipment Market Association) lobby to protect access to ethanol-free fuel for classic vehicles.

Taking proactive steps now—upgrading vulnerable components, using ethanol-free fuel when possible, and following proper storage procedures—protects your investment and ensures your classic car remains reliable for years to come. The alternative is expensive repairs and frustrating breakdowns that could have been prevented with relatively simple preventive measures.