Can I Use E87 Instead Of E85? | Fuel Facts

Using E87 in a vehicle designed for E85 is generally not recommended due to significant differences in ethanol content and engine tuning.

Pulling up to the pump, it’s easy to feel a bit overwhelmed by the different fuel options available. We see terms like E85, E15, and the familiar E87, and it naturally sparks questions about what’s compatible with our vehicles. Understanding the specific requirements of your engine is key to keeping your vehicle running smoothly and efficiently.

Decoding Ethanol Blends: E85, E87, and Beyond

The numbers associated with fuel types often indicate their ethanol content. This percentage is a critical factor for how an engine processes the fuel, impacting everything from combustion to fuel system longevity.

What is E85 Fuel?

E85 is a high-ethanol blend fuel, typically containing between 51% and 83% ethanol by volume, though it’s often marketed as “up to 85% ethanol.” This fuel is exclusively for Flex Fuel Vehicles (FFVs), which are specifically engineered to run on either E85 or conventional gasoline. E85 has a lower energy density than gasoline, meaning a greater volume of E85 is required to produce the same amount of energy as gasoline. It also boasts a higher octane rating, often around 100-105 RON, which can be beneficial for performance in engines tuned to take advantage of it.

What is E87 Gasoline?

E87 refers to standard unleaded gasoline with an 87 Anti-Knock Index (AKI) octane rating. In most parts of the country, this fuel contains up to 10% ethanol by volume, making it an E10 blend. This is the most common and widely available type of gasoline, designed for the vast majority of conventional gasoline-powered vehicles on the road. The small percentage of ethanol in E87 (E10) is generally well-tolerated by modern gasoline engines and fuel systems.

The Core Difference: Ethanol Content and Octane Rating

The primary distinction between E85 and E87 lies in their ethanol content. E85 is predominantly ethanol, while E87 (as E10) is predominantly gasoline with a minor ethanol component. While both fuels have an octane rating, the higher octane of E85 is a byproduct of its ethanol content, not its defining characteristic for compatibility.

An engine’s fuel system and control unit are calibrated to specific fuel properties. The high ethanol concentration in E85 significantly changes the fuel’s chemical properties and combustion characteristics compared to gasoline or E10. This requires specialized components and engine management systems.

Can I Use E87 Instead Of E85? Understanding the Risks

Attempting to use E87 (E10) in a vehicle designed for E85 can introduce several operational and mechanical issues. The engine’s computer, expecting a high-ethanol fuel, will attempt to adjust fuel delivery based on that expectation.

Table 1: Fuel Ethanol Content Comparison

Fuel Type	Ethanol Percentage (typical)	Octane Rating (typical)
E85	51-83%	100-105 RON
E87 (E10)	Up to 10%	87 AKI
E0 (Pure Gas)	0%	Varies (often 87-93 AKI)

Impact on Flex Fuel Vehicles (FFVs)

Flex Fuel Vehicles are equipped with sensors that detect the ethanol concentration in the fuel tank. The engine control unit (ECU) then adjusts fuel injection timing, ignition timing, and air-fuel ratio to optimize performance for the detected blend. When an FFV designed for E85 is filled with E87 (E10), the ECU will detect a much lower ethanol content than it would for E85.

The ECU will compensate by reducing the amount of fuel injected, assuming it’s still dealing with a high-ethanol fuel. This results in the engine running lean, meaning there isn’t enough fuel for the amount of air entering the engine. A lean condition can cause reduced power, increased exhaust gas temperatures, and potentially lead to pre-ignition or engine knocking, which can damage internal engine components over time. You might notice a “Check Engine” light illuminating as the system struggles to adapt.

What About Non-FFVs?

Conventional gasoline vehicles are not designed to handle E85. The high ethanol content of E85 is corrosive to fuel system components (hoses, seals, fuel pumps, injectors) in non-FFVs, which are typically made of materials incompatible with such high ethanol concentrations. Using E85 in a non-FFV will quickly lead to severe fuel system degradation, leaks, and engine failure. Using E87 (E10) in a non-FFV is standard and acceptable, as these vehicles are built to tolerate up to 10% ethanol.

Why E85 Demands Specific Engineering

The ability to run on E85 requires significant engineering differences in a vehicle’s design. These adaptations ensure both performance and durability when using a high-ethanol fuel.

• Material Compatibility: Fuel lines, seals, O-rings, and other components in the fuel system must be constructed from ethanol-resistant materials to prevent corrosion and degradation.
• Fuel System Capacity: Because E85 has lower energy density, an engine needs to burn a greater volume of it to produce equivalent power. This means FFVs are equipped with larger fuel injectors and a higher-capacity fuel pump to deliver the necessary fuel flow.
• Engine Management System: The ECU in an FFV has specialized programming. It uses an ethanol sensor to determine the blend ratio and dynamically adjusts fuel mapping, ignition timing, and cold-start enrichment strategies across a wide range of ethanol concentrations, from E0 to E85. According to the NHTSA, these specialized fuel systems adhere to rigorous safety and performance standards.

Recognizing a Flex Fuel Vehicle

Identifying whether your vehicle is an FFV is straightforward. There are several clear indicators:

• A yellow fuel filler cap or a yellow ring around the fuel filler opening.
• A “Flex Fuel” or “E85” badge on the vehicle’s exterior, often on the trunk lid or fenders.
• The owner’s manual explicitly states E85 compatibility. This is the most reliable source of information.
• The vehicle’s VIN (Vehicle Identification Number) can be checked; the 8th digit often indicates FFV capability (e.g., “Z” or “V” for some manufacturers).

According to the EPA, clear labeling and owner’s manual information are crucial for consumers to make correct fuel choices and ensure proper vehicle operation.

The Risks of Misfueling and Engine Performance

Misfueling, or using the wrong type of fuel, can lead to a range of performance issues and potential damage. The engine’s attempt to compensate for an unexpected fuel blend can only go so far before problems arise.

Table 2: Potential Engine Impacts of Incorrect Fuel

Fuel Intended	Fuel Used	Potential Issues
E85 (FFV)	E87 (E10)	Lean running, reduced power, higher combustion temperatures, increased emissions, long-term engine wear, “Check Engine” light.
E87 (E10) (Non-FFV)	E85	Fuel system corrosion/degradation, severe engine damage, drivability issues, immediate “Check Engine” light, warranty void.

When an FFV runs E87 instead of E85, the ECU’s adjustments might prevent immediate catastrophic failure, but the engine will operate outside its optimal parameters. You may experience reduced horsepower and torque, diminished fuel economy, and a general lack of responsiveness. Over time, sustained lean conditions can lead to carbon buildup on valves, premature wear of oxygen sensors, and stress on catalytic converters, leading to costly repairs.

Always Check Your Owner’s Manual

The definitive guide for your vehicle’s fuel requirements is always the owner’s manual. Manufacturers invest significant resources in engineering and testing their vehicles to perform optimally with specific fuel types. The manual provides precise recommendations for octane ratings and acceptable ethanol blends. Relying on this official documentation ensures you are using the fuel that your vehicle was designed to consume, promoting its longevity and maintaining its performance characteristics.

Operating outside these guidelines, even if the vehicle seems to run, can compromise engine health and potentially void portions of your warranty. It is always better to follow the manufacturer’s recommendations for fuel type.