Can You Mix E85 With 87? | Fueling Your Ride Right

Mixing E85 with 87 octane gasoline is generally not recommended for most standard vehicles due to potential engine damage and performance issues.

You pull up to the pump, and there it is: E85, often with a tempting price tag. It’s easy to wonder if you can just blend it with your usual 87 octane. The thought might cross your mind to save a few bucks or just use what’s available.

As a mechanic, I’ve seen the results of this confusion firsthand. Understanding what’s under the hood and in the tank is key to keeping your vehicle running smoothly.

Understanding E85 and 87 Octane Gasoline

Let’s break down what these two fuels are made of. They might both be “fuel,” but their compositions are quite different.

Standard 87 octane gasoline, the regular stuff most cars run on, typically contains up to 10% ethanol. This is often labeled as E10.

E85, on the other hand, is a high-ethanol blend. It contains between 51% and 83% ethanol, with the rest being gasoline. The “85” in E85 refers to the maximum ethanol content.

Ethanol is an alcohol, and it behaves differently from gasoline. It’s more corrosive and has a lower energy density than pure gasoline.

Here’s a quick comparison:

Feature	87 Octane Gasoline (E10)	E85 Fuel
Ethanol Content	Up to 10%	51% to 83%
Octane Rating	87 AKI (Anti-Knock Index)	~100-105 AKI
Energy Density	Higher	Lower

The higher octane rating of E85 might seem like a benefit. However, a higher octane fuel is only beneficial if your engine is designed to take advantage of it.

Most standard vehicles are calibrated for gasoline with a much lower ethanol content. Their fuel systems and engine management systems are not built for E85.

Can You Mix E85 With 87? The Short Answer and The Why

For the vast majority of vehicles on American roads, the answer is a clear no. You should not mix E85 with 87 octane gasoline.

This isn’t just about octane numbers. It’s about the entire fuel system and how your engine is designed to operate.

Mixing these fuels can cause a range of problems, from immediate performance issues to long-term damage.

The primary reason for this incompatibility lies in ethanol’s properties:

• Corrosiveness: Ethanol can degrade rubber and plastic components in a fuel system not designed for it.
• Lower Lubricity: Ethanol provides less lubrication than gasoline, which can strain fuel pumps and injectors.
• Stoichiometric Ratio: Ethanol requires a different air-to-fuel ratio for efficient combustion.
• Water Absorption: Ethanol attracts and absorbs water, which can lead to corrosion and fuel separation.

Your vehicle’s Engine Control Unit (ECU) is programmed for a specific fuel type. It expects a certain oxygen content in the exhaust gases to adjust fuel delivery.

When you introduce a high-ethanol blend, the ECU struggles to compensate. It tries to richen the mixture, but it often reaches its limits.

What Happens When You Mix E85 and 87 Octane?

When you put E85 into a non-flex-fuel vehicle’s tank, even mixed with 87 octane, several things can happen.

The immediate effects can include:

• Rough Idling: The engine struggles to maintain a steady RPM.
• Reduced Power: You’ll notice a significant drop in acceleration and overall performance.
• Check Engine Light (CEL): The ECU will detect out-of-range fuel trim values and illuminate the CEL.
• Misfires: Inconsistent combustion can lead to engine stumbling.
• Poor Fuel Economy: E85 has less energy per gallon, so your vehicle will consume more fuel to travel the same distance.

These are just the short-term symptoms. Over time, the damage can become more severe and costly.

Long-term consequences for a standard vehicle running on E85 or a mix include:

1. Fuel System Degradation: Ethanol can dry out and crack rubber fuel lines, seals, and O-rings.
2. Fuel Pump Failure: The pump works harder and may not be adequately lubricated, leading to premature failure.
3. Injector Clogging: Ethanol can dissolve deposits in the fuel tank and lines, sending them to clog injectors.
4. Sensor Damage: Oxygen sensors and fuel level sensors can be affected by the different fuel composition.
5. Catalytic Converter Damage: Rich fuel mixtures can overheat and damage the catalytic converter.

The EPA and DOT set standards for fuel compatibility. Vehicle manufacturers design their cars to meet these standards using specific fuel types. Deviating from the recommended fuel type can void your warranty for fuel system components.

Flex-Fuel Vehicles: The Exception

There’s a specific type of vehicle designed to run on E85, gasoline, or any mixture of the two. These are called Flex-Fuel Vehicles (FFVs).

FFVs have specialized components that can handle the high ethanol content.

Key differences in FFVs include:

• Corrosion-Resistant Materials: Fuel lines, fuel pumps, and injectors are made from stainless steel or other ethanol-resistant materials.
• Specialized Fuel Sensor: An ethanol sensor detects the ethanol concentration in the fuel tank.
• Adaptive ECU: The engine’s computer is programmed to adjust fuel delivery, ignition timing, and other parameters based on the detected ethanol content.
• Heated Oxygen Sensors: These help the ECU make accurate air-fuel ratio adjustments even with high ethanol content.

If you own an FFV, mixing E85 with 87 octane gasoline is perfectly fine. The vehicle’s system is built to handle the varying ethanol levels without issue.

It’s important to know your vehicle’s capabilities. Don’t assume your car is an FFV just because E85 is available at the pump.

Recognizing a Flex-Fuel Vehicle

How do you know if your vehicle is an FFV? There are several clear indicators.

The most common signs are:

1. Yellow Gas Cap: Many FFVs have a distinctive yellow fuel filler cap or a yellow ring around the filler neck.
2. “Flex-Fuel” or “E85” Badge: Look for a badge on the vehicle’s exterior, often on the trunk lid or fender.
3. Owner’s Manual: Your vehicle’s owner’s manual will explicitly state if it is an FFV and compatible with E85.
4. Fuel Door Label: Some vehicles have a label inside the fuel filler door indicating E85 compatibility.
5. VIN Decoder: You can check your vehicle’s VIN (Vehicle Identification Number) with a decoder tool online or through a dealership.

Always check these indicators if you are unsure. Relying on guesswork can lead to costly repairs.

The NHTSA (National Highway Traffic Safety Administration) and EPA (Environmental Protection Agency) oversee vehicle and fuel standards. Manufacturers clearly label FFVs to avoid confusion.

Here’s a comparison of common fuel system components:

Component	Standard Vehicle	Flex-Fuel Vehicle
Fuel Lines	Rubber/Plastic (E10 compatible)	Stainless Steel/Ethanol-resistant
Fuel Pump	Standard materials	Ethanol-compatible, higher flow
Fuel Injectors	Standard design	Ethanol-resistant, larger flow capacity
Engine Control Unit (ECU)	Fixed gasoline calibration	Adaptive for varying ethanol levels

If your vehicle doesn’t have these specific FFV features, it’s designed for gasoline, and that’s what it needs.

Accidental Mixing: What to Do

Mistakes happen. If you accidentally put E85 into a non-flex-fuel vehicle, don’t panic. The severity of the situation depends on the amount of E85 added.

If you’ve only added a small amount, perhaps a gallon or two, and the tank is mostly full of 87 octane, you might be okay.

Here’s what to do:

1. Do Not Start the Engine (if possible): If you realized the mistake immediately after pumping, don’t turn the key.
2. Top Off with 87 Octane: If you’ve only added a small amount of E85, fill the rest of the tank with premium 87 octane gasoline. This helps dilute the ethanol concentration.
3. Drive Gently: If you must drive, do so gently and avoid heavy acceleration. Listen for any unusual engine noises or performance issues.
4. Monitor for Symptoms: Watch for the Check Engine Light, rough idling, or reduced power.
5. Seek Professional Help: If you’ve added a significant amount of E85 (more than a quarter tank) or if your vehicle is showing clear symptoms of distress, it’s best to have it towed to a mechanic.

A mechanic can drain the fuel tank and refill it with the correct fuel. They can also check for any immediate damage or error codes.

Ignoring the problem can lead to expensive repairs down the road. It’s always better to address fuel mix-ups promptly.

Remember, the goal is to keep your engine happy and healthy. Using the right fuel is a big part of that.

Sticking to the manufacturer’s recommendations for fuel type is always the safest and most economical choice in the long run.

Can You Mix E85 With 87? — FAQs

What is the main risk of mixing E85 with 87 octane in a non-FFV?

The primary risk is damage to the fuel system components, such as fuel lines, seals, and the fuel pump, due to ethanol’s corrosive nature. The engine’s computer also cannot properly adjust for the high ethanol content, leading to poor performance and potential long-term engine issues. This can result in costly repairs that could have been avoided.

Will mixing E85 and 87 octane immediately damage my engine?

Not necessarily immediately, but it can cause immediate performance problems like rough idling, reduced power, and a lit Check Engine Light. The extent of damage depends on the amount of E85 added and how long the vehicle is operated with the incorrect fuel. Continuous use will certainly lead to accelerated wear and component failure.

How can I tell if my car is a Flex-Fuel Vehicle (FFV)?

Look for a yellow gas cap, a “Flex-Fuel” or “E85” badge on the vehicle’s exterior, or check your owner’s manual. Some vehicles also have a label inside the fuel filler door indicating E85 compatibility. These indicators are intentionally clear to prevent accidental misfueling.

What should I do if I accidentally put E85 in my non-FFV?

If you’ve only added a small amount, top off the tank with 87 octane gasoline to dilute the mixture. Drive gently and monitor for symptoms. If you’ve added a significant amount or experience issues, do not drive the vehicle and have it towed to a mechanic to drain the tank. Prompt action minimizes potential damage.

Does mixing E85 with 87 octane increase my vehicle’s performance?

No, for a non-flex-fuel vehicle, mixing E85 with 87 octane will actually decrease performance and fuel economy. While E85 has a higher octane rating, a standard engine cannot utilize this benefit and will struggle to combust the fuel efficiently. It will run poorly and potentially cause internal engine stress.