Driving down the highway, you glance down and realize your fuel tank is nearly empty. You pull into the next gas station you see, hastily swipe your card at the pump marked “premium,” and start filling up your regular old Honda Civic. Wait a second – didn’t you normally put regular gasoline in your car? Uh oh.
Can you mix premium and regular gas? It’s a question that’s crossed every driver’s mind at some point. Whether you accidentally grabbed the wrong pump handle or are wondering if premium fuel will give your aging car a boost, combining gas grades is a tricky topic.
The short answer is: it’s not recommended to mix gasoline octane levels. While premium gasoline does have some advantages, combining grades can cause anything from short-term engine knocking to extensive long-term damage.
However, the effects really depend on your specific vehicle and how often you mix fuel grades. Doing it once in a blue moon likely won’t cause catastrophic effects. But consistently alternating between gas types definitely isn’t a good idea.
Below, we’ll explore everything you need to know about mixing premium and regular gasoline including:
- How premium and regular gas differ
- The potential risks of combining fuel grades
- Signs that your car isn’t happy with mixed gas
- What to do if you’ve already mixed premium and regular
- Tips to avoid mixing gasoline grades in the future
So buckle up and get ready for a deep dive on this gas station faux pas. Just try not to panic next time you accidentally grab the wrong pump handle – this guide will cover all you need to know about mixing gas octane ratings.
Table of Contents
The Difference Between Regular and Premium Gasoline
Before we get into the implications of combining different fuel types, let’s quickly cover what makes them unique in the first place. Why does premium gas cost more, and what are you paying for?
The main difference between regular, mid-grade, and premium gasoline comes down to octane rating. This value represents the fuel’s resistance to engine knocking and pre-ignition.
Regular gasoline typically has an octane rating around 87, mid-grade is 89, and premium fuel sits between 91-93 octane. Some stations even offer super or ultra premium gasoline, boasting octane levels of 94 or higher.
Higher octane ratings mean the gasoline can withstand compression before igniting. This gives it a wider margin of error in high performance engines before abnormal combustion occurs.
Premium’s higher octane content makes it less prone to:
- Engine knocking – when fuel ignites prematurely in the cylinder
- Pre-ignition – when the air/fuel mixture ignites before the spark plug fires
Both knocking and pre-ignition can reduce performance and cause long-term engine damage over time.
Beyond resisting engine stress, many premium gasolines also contain more detergents and cleaning additives. These formula variations help remove carbon deposits that can build up on fuel injectors and other combustion components.
However, the extra cleansing agents aren’t always necessary. Many newer regular gasolines also contain sufficient injector cleaners.
So in summary, the main differences between gasoline grades are:
- Octane rating – Premium has a higher rating meaning more resistance to abnormal combustion.
- Detergent additives – Premium sometimes contains more cleaning agents to reduce deposits.
These differences explain the typical $0.20 – $0.60 per gallon premium you pay at the pump for the upgraded fuel. For most regular passenger vehicles, sticking with 87 octane regular gasoline is perfectly fine. Higher grades are really only required for performance engines, towing, or high compression motors.
But what happens if you inadvertently mix up gasoline grades between fill ups? Or intentionally combine them hoping for improved performance? Let’s dig into the implications next.
Potential Issues with Mixing Gasoline Octane Ratings
Gasoline is a highly engineered product. Extensive research goes into creating additives and formulas optimized for different vehicles. So not surprisingly, auto manufacturers recommend against alternating or mixing fuel grades.
Drivers combining gasoline types usually fall into one of two camps:
1. Accidental mixing – Not realizing regular gas is in the tank already and adding premium, or vice versa.
2. Intentional mixing – Hoping higher octane premium will boost performance or efficiency in a regular car.
Regardless of why you mixed fuel grades, here are some potential consequences to be aware of:
Engine Knocking and Pre-Ignition
The most immediate symptom is sporadic engine knocking or pre-ignition events. Remember, higher octane premium gasoline resists irregular combustion better.
If you fill up a car requiring 91+ octane fuel with 87 octane regular by mistake, the probability of knocking and pre-ignition rises. The engine isn’t designed to run on lower octane fuel.
On the flip side, putting premium gas in a regular car can also cause pinging and knocking. Why? The engine’s timing isn’t optimized for the higher octane rating.
Inconsistent ignition or uncontrolled combustion reduces efficiency and performance. Prolonged issues can also damage internal components like pistons over time.
Check Engine Light Illumination
Another consequence of mixed gasoline grades is illumination of the check engine light. Knock sensors hear the abnormal combustion and pinging. This triggers an error code related to ignition timing or fuel delivery.
If the engine computer detects persistent knocking, it will try to adjust spark timing. But this still may not resolve the root cause, leading to emission or performance related fault codes.
In some cases the check engine light is just temporary while using the mixed fuel grades. But it could point to larger issues if you continue alternating gasoline octane ratings long term.
Buildup and Deposit Accumulation
Mixing grades can also accelerate buildup and deposit formation in your engine over time. This stems from the extra detergents found in some premium gasoline formulations.
Detergents help remove carbon deposits from fuel injectors and combustion chambers. But they can also inadvertently dislodge deposits accumulated from using regular gas.
These looser carbon deposits may travel through the fuel system, eventually clogging components like fuel filters. Oxygen sensors can also get coated.
While premium fuel’s detergents clean some areas, they paradoxically create buildup in other places over time when mixed with regular gas.
Reduced Fuel Economy
All the issues above like engine knocking, error codes, and deposit accumulation can negatively impact your vehicle’s fuel efficiency.
Abnormal combustion wastes energy. Deposits reduce oxygen sensor accuracy. Your engine constantly adjusting timing to compensate burns more fuel.
While the fuel economy drop may only be 1-3 mpg from mixing gasoline grades once, over months or years it really adds up. Sticking with a consistent octane rating optimizes efficiency.
Long-Term Internal Wear
Finally, inconsistent gasoline grades cause uneven thermal and friction stresses inside your engine. Knocking subjects components like piston rings and cylinder walls to higher pressures and temperatures.
Over tens of thousands of miles, this accelerated wear can shorten the lifespan of gaskets, bearings, cylinder bores, and other internal engine parts. For high-performance motors, this long-term damage is even more pronounced.
The One Exception
Now, all these dire warnings don’t mean you can never ever mix gasoline grades in an emergency.
If you run completely out of gas far from a station and need to get your car started again, adding a couple gallons of premium to your otherwise empty regular gas tank is fine.
The minimal amount of higher octane fuel mixed in likely won’t cause extensive issues beyond maybe some short-term knocking. It’s a last resort hack that beats getting towed or stranded.
Outside very specific situations like that, mixing gasoline grades routinely is asking for trouble. Don’t intentionally combine fuel types hoping for increased horsepower or efficiency either.
Next let’s cover how to recognize when your car is unhappy with mixed gasoline so you can address it.
Signs Your Car is Disliking Mixed Gasoline
If you’ve accidentally or intentionally used mixed gasoline grades recently, here are some symptoms to watch out for:
- New engine knocking, pinging or pre-ignition sounds
- Illumination of the check engine or reduced performance warning
- Loss of power during acceleration
- Increased exhaust popping or backfiring
- Rougher engine idle
- Jumpiness or stumbling sensation while driving
- Fouled spark plugs upon inspection
- Worst case – noticeable loss in fuel economy
Hearing new metallic knocking noises from under the hood is one of the most common indicators of mixed fuel grades. It usually manifests at mid-range RPMs or under acceleration.
The check engine light coupled with ignition or fuel related codes is another sign of mixed gas consequences. Most vehicles’ onboard computers can compensate reasonably well to avoid serious issues. But the ECU may still detect and log abnormalities.
Letting the fuel tank run quite low before refilling with the proper gasoline grade is the best way to remedy the situation. But if symptoms persist or engine damage is suspected, actions like replacing the spark plugs, fuel filter, or using additives may help remove some deposit buildup.
Getting a full professional fuel system cleaning service after mixing gas grades for an extended time is also a smart proactive measure.
Next let’s go over steps to take if you’ve already inadvertently mixed fuel octane levels.
What to Do if You’ve Already Mixed Gasoline Grades?
Okay, so you realized too late that you pumped the wrong octane fuel into your tank. It happens. Don’t freak out or do anything drastic. Here are some smart next steps:
1. Use up the mixed tank normally before refilling. Let the blended gasoline run through the system so fresh consistent fuel can replace it. Avoid topping off.
2. Listen for any knocking or pinging. Be alert for any new sounds indicating the mixed fuel is causing combustion issues.
3. Consider using a fuel injector cleaner additive. This can help remove some carbon deposits or buildup from switching gas grades.
4. Replace air and fuel filters at next service. They may capture some debris dislodged by cleaning agents.
5. Switch back to your normal fuel grade at next fill up. Never mix or alternate gas grades within the same tank.
6. Get an engine tune up or fuel system cleaning if needed. This is especially helpful if you’d been alternating fuel grades long term.
Aside from being vigilant for any performance changes or knocking after using mixed gas, your vehicle should be fine in the short term.
The worst problems arise from repeatedly switching back and forth between gasoline octane levels over months or years. Try your best to avoid it.
But stressing over a single mix up or using the wrong pump once in a blue moon won’t cause major issues alone. Just refill with your normal fuel grade and keep driving like usual.
Tips to Avoid Mixed Gas Grades in the Future
If accidentally combining fuel types is a recurring issue for you, here are some tips to avoid gasoline mix-ups down the road:
- Put an octane rating reminder in your fuel filler door – Use a sticker or marker to note whether your car needs regular, mid-grade or premium.
- Set a reminder on your phone – Program a periodic reminder about your vehicle’s fuel type so it’s top of mind.
- Use the same pump every time – Always go to the same pump labeled for your octane rating at your preferred gas station.
- Fill up more frequently – Don’t let the tank get super low before refueling. This minimizes the amount of mixed fuel.
- Pay attention to the pump – Don’t start gassing up on autopilot. Take a second to confirm the right octane grade.
- Use a fuel additive – Additives like Techron can help clean deposits that accumulate from switching gasoline grades.
Following these simple tips will make accidentally mixing up fuel grades much less likely. But should it still happen, now you have all the details on how gasoline octane ratings work and the potential consequences of combining them.
The most important takeaway is to never intentionally mix gasoline types in your vehicle’s tank. Always run one full tank of consistent fuel before switching grades when required. Be extra vigilant when filling up to avoid pumping the wrong octane rating.
While mixing premium and regular gas on occasion won’t catastrophically ruin your engine, it’s still not recommended. Following proper fueling practices and the steps outlined in this guide will keep your car running smoothly for the long haul.
Accidentally grabbing the wrong pump handle happens to all of us eventually. And premium gasoline does seem tempting with its claims of reduced engine knock and super cleaning detergents.
But resist the urge to mix fuel grades – inconsistent octane ratings can cause anything from short-term driveability issues to extensive engine damage over time.
Always be attentive when fueling up and stick to the octane rating your owner’s manual specifies. If you do end up with mixed gasoline, use up the tank and get back to a consistent fuel grade as soon as possible.
While combining premium and regular gas once in a blue moon won’t destroy your engine, it’s still not recommended. Following the tips in this guide will keep your car running happy on the right fuel. So next time you absentmindedly grab the wrong pump handle, take a deep breath and refer back to the steps outlined above. Your vehicle will be fine!