Fuel Octane, Choosing The Wrong Octane Will Cost You

This is more of a clarifying post, rather than advice or tips. It’s about fuel octane, when to choose what octane for your vehicle, and what the wrong octane will do.

Why? Because I’ve heard so many people talk about how they ‘threw some high octane’ in their car ‘to get more performance’.

First the basics. What is the octane rating you see on every fuel pump everywhere?

Without getting technical and beyond the scope of this article, octane is a measure of gasoline’s anti-knocking properties. What is anti-knocking? Well, simply put knocking is a condition in which fuel burns too early in the combustion process, also called pre-detonation or pinging. It’s the instability of gasoline that causes it to burn prematurely and unstably. The higher the octane, the more stable the gasoline.

IMPORTANT: Higher octane gasoline, which is more stable, has no more energy potential than lower octane gasoline. There is no more energy to be had from high octane gasoline, then from low octane gasoline.

What octane gasoline should I be using in my car?

Use only what the owner’s manual specifies. If your car is designed to run on regular gasoline, or 87 octane. If your manual specifies higher octane fuel, such as 89, 91, or 93 use the closest octane rating available at your gas station without going below the specified rating in your manual.

What will happen if I use higher octane gas than I’m supposed to?

A few things. For one, you will be wasting a huge amount of money paying for high octane gasoline. Second, your car will not run correctly, whether you notice it or not. Higher octane fuel requires more heat and more precision to burn correctly. If your car is designed to burn 87, it will not burn 93 correctly. Third, your gas mileage will suffer. The inability of your engine to burn the higher octane gas correctly will cause your engine to produce less power and thus will require more fuel to perform at the same level.

What about using lower octane gasoline in a high octane engine?

In this situation, you will see negative effects that could be even worse. Using low octane fuel in a high octane engine will result in severely reduced performance because the engine will attempt to adjust to the lower octane gasoline. In extreme cases, or with prolonged use of low octane gasoline in these engines, pinging or pre-detonation can occur and can eventually destroy your engine. Pre-detonation causes very hot conditions in your engine and can melt sparkplug and pistons.

What fuel you use in your vehicle is important. Make sure you always follow the manufacturers recommendations. Using a fuel other than what the manufacturer specifies will in no way help you save money, gain power, or do anything other than cost you money.

Did you accidentally fill up with 87 instead of 91 or 93? Were you in a pinch and had to fill up with lower octane fuel? Not a problem. If your tank is full, and adding high octane fuel is not an option, consider picking up a bottle of Lucas Octane Boost. One bottle will treat an entire tank of gas and help to bring your octane closer to where it should be. It’s not a fix all, and certainly shouldn’t be used in place of actually filling up with the correct fuel, but if you had to add some low octane fuel for one reason or another, it can help out in a pinch. Amazon has the lowest price I’ve seen on this, and purchasing through this affiliate link helps me keep this site going. Again, don’t go thinking that you can fill up with 87 and drop a bottle of this in to save money. That’s not how it works. But it can help to ease the effects of lower octane fuel in an engine that requires high octane.

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26 comments to Fuel Octane, Choosing The Wrong Octane Will Cost You

  • My small car is rated at 87 octane but I need to burn 89 octane to prevent pinging. I’ve had the car tuned and timing adjust a couple of times, but 87 octane doesn’t cut it and I must use 89. Any suggestions?

  • Gerald Sims Jr.

    I have been using 93 octane in my 2001 Taurus SES FOR about 4 years I JUST found out Ineeded to be using 87 octane can I go to the 87 octane or do I NEED TO KEEP using the higher octane I also found out my wife,s car a Ford Focus uses 87 but she had been using 89 octane what can WE do

  • Sherry Black

    I made the dumb mistake of pushing the wrong button at the pump. I put 89 octane in my 2000 Ford Mustang GT when it should be 87 octane. I filled the entire tank up with the 89! Should I drive until my tank is low again or start adding the 87 octane at intervals? Appreciate any help! I love my Mustang and would hate to ruin my 11 years of a great experience.

  • Dustin

    gas is gas…use the 87 it will cost less and burn faster but the higher octane cost more and burns slower its pretty much even and in fact has been proven that the higher octane cost more overtime anyway

  • Tommie Bell

    My 2005 s-type 4.2 Jag. requires 95 octane but the highest I can find in my city is 93, what would you suggest? I keep getting carbon build up, which is costly to have that cleaned.

  • Jarv

    I have a 2011 Subaru Legacy 2.5GT. And in the manual it says it requires 95 or above. I have been using 100 octane for more than 3 months now. Will that ruin my engine? The car manufacturer said that it runs best on 97 octane. What should i do?

  • Emil adrian fernandez

    My fuel tank cover says – use 95+ octane. What does + meas? The higher the beter? Thanks

  • David

    If you can’t get 95 octane rating and the best you can get is 93, fill up with 93 then add a bottle of octane boost which you can get at any service station or auto supplies outlet.

  • John

    In most cases with engines within the last 10 years they have used a knock sensor. It allows even a high octane engine to use 87 but at a reduced performance level. The knock sensor saves the engine from pinging and damage.

  • Nate

    If you are worried about ruining your car, you really cant hurt it as much as you think with going a tiny bit over on octane. Just dont go UNDER! in europe, the lowest they even sell as regular is about 90 or 91 octane. in the usa honestly companies are knowingly selling crappier gas because they know that the general public have no idea what they are buying. and the ethanol percentage can legally go unlisted as long as its under 10%. GET an octane booster (i love the Lucas Oil 3x boost, find it at autozone or napa or wherever)(red bottle) and test it out on your vehicle. the only way you can screw it up is if you are supposed to be using Diesel, really.. you can go well over 93, ive ran 100 blend in my car before. yes, its overkill, no it wont hurt your car. its higher quality and depending on the model you may get that better performance you need. Even if you usually run 87, just putting 20 percent of a tank of 91 will bring you up to mid grade. its really that simple. no worries.

  • Carl

    I used 87 octane in my 93 Acura Vigor.. Supposed to use premium… Engine check light went on… I used premium and check light went off… Another words 87 was causing an issue.. I decided to use 87 and perform a smog test.. The timing failed and needed to be advanced. Another words just stick to what the manufacturer specifies.

  • Robert

    No Offense But Your Correct And Incorrect Yes Higher Octane Is More Stable But Also A Higher Octane Means The Fuel Will Burn Cooler You Will Get More Power With a Higher Octane I Know This Because If I Run 87 In My Car I Get 400Hp If I Run 110 octane I Get 475-500 (Depending On The Weather) Your Correct But U Need To Re Think What U Say B4 U Teach People The Wrong thing

  • Colton

    Robert, you are comparing race gas to unleaded pump gas. Race gas is scientifically engineered with power-producing parameters and additives that are designed to release more potentially energy upon combustion. Pump gas is engineered entirely different and has to comply with 99.9% of cars on the road. There will not be peak horsepower increases in the varying octane fuels however, the temperature that the fuels combust at is different allowing the engine to produce more efficient power. You sir, need to rethink what you say before you compare an additive based, high-octane performance enhancing fuel to an everyday pump gas octane.

  • Paul

    I have an 81 Ford pickup. I used 87 octane non-corn oil gas until the government took it away from us in MT. I got better mileage and more power. The slight increase in cost was well worth it. When they took our 87 octane away from us I had to go to the corn juice now I’m back to less power and about 20% poorer mileage.

  • Frank

    What a misleading pile of garbage this article is. You should be ashamed of yourselves for lying to people like this. And then to push the Lucas Octane boost at the end. What a complete joke.

  • […] Fuel Octane, Choosing The Wrong Octane Will Cost You | What Could Be Greener What will happen if I use higher octane gas than I’m supposed to? A few things. For one, you will be wasting a huge amount of money paying for high octane gasoline. Second, your car will not run correctly, whether you notice it or not. Higher octane fuel requires more heat and more precision to burn correctly. If your car is designed to burn 87, it will not burn 93 correctly. Third, your gas mileage will suffer. The inability of your engine to burn the higher octane gas correctly will cause your engine to produce less power and thus will require more fuel to perform at the same level. Carbon buildup and octane rating | Mechanical /Maintenance Forum | Bob Is The Oil Guy People here talk about using higher than rated octane causing carbon build up. […]

  • anonomous

    I believe this info was helpful but a bit confusing and off in some ways. The fuel that should be used in you engine will be noted somewhere on you car, just stick to the recommended stuff. Going over won’t help unless you found your engine was pinging, going under is a bad idea but if you have no other choice use it. When using a lower octane on a modern engine the managment compensates for the pinging, but just avoiding hard driving would help older systems. When you think of using alcohol fuels remember, ethanol has a lower energy content but boosts octane. High compression or forced induction engines may benefit from this if they where designed to. As for modified engines, depending on the extent, have to go higher then the recommended. If you have to go to ethanol to avoid pinging just remember you have to re-adjust your fueling system to get the extra fuel to keep a good A/F ratio. In the end: higher compression/boost –> higher octane simple as that.

  • anonomous

    Also I forgot to note about using higher then needed octane, it will not harm your engine(the rating they recommend is the minimum required) and depending on your altitude would be a safe bet to go 1 rating higher, that should remove any chance of pinging. As for the possible gain in power, fuel additives differ and higher octane is a more pure form of fuel so the specific energy may differ. Where I come from we only have 93 and 95, my car is recommended to use 91, but I “have to” use 93 but if 91 was available I would use it seeing as I live at a high altitude and chance of pinging is reduced, but if I go to the coast I would personally prefer 1 rating higher just to be safe.

  • […] Fuel Octane, Choosing The Wrong Octane Will Cost You | What Could Be Greener It is amazing that people still believe that high octane fuel performs correctly in low compression engines. […]

  • Buckshot Bob

    Well, I gotta say all this baloney about higher or lower octane is exactly that….baloney!! Buckshot Bob’s been using a mixture of good ol CNG and 87 octane in Big Red for two years now. Let me tell you Big Red’s been getting over 40 mpg consistently. By the way, Big Red is a Chevy Silverado 2500. I know what your thinking…….that’s amazing! Well, it truly is. Nothing wrong with a little Appalachia ingenuity to get things right. All you fine folks out there probably thought the only thing that comes out of Appalachia is kissing cousins. Well, YOUR WRONG!!

  • […] I get the highest mpg on that brand for reasons unknown to me. This article nailed it, mostly: Fuel Octane, Choosing The Wrong Octane Will Cost You | What Could Be Greener He didn't mention carbon build-up, another impact of using higher octane gas in a low compression […]

  • Kevin

    Thank you sir. You have just owned everybody else in this argument.

  • lawson

    In my honda jazz manual it says “designed to run on petrol of RON91 or higher”. I would take it as statement for its minimum required petrol RON – not be reflecting the actual RON of petrol they use it for their test run or even for its dynamo run for torque curve & rpm vs hp. Using RON91 would most likely cause the engine ECU to retard igition so much that the engine would loose more than 5% efficiency. From the web most new NA engine had compression ratio of 9:1 by 1985 and 10:1 by 1995. For year 1975 new engine the compression ratio could be as low as 7.8:1. For honda jazz compression ratio of 10.3:1 and being not the DI type engine I reckon that RON95 petrol would be give the most optimum dollar:km/litre benefit, unless RON97 petrol price is higher by not more than 5%. I do wish that Honda would just print the milage vs RON in honda jazz manual something like: RON91 15km/litre@90km/hr. RON 95 17.5km/litre@90km/hr. RON97 18.5km/litre@90km/hr. It would certain make our decision making on RON selection much easier.

  • Tommy Nguyen

    After using the correct gas (Couple tank fulls later),does pinging go away?

  • Butch

    In Saudi Arabia the same cars are running on 91 and 95 because that’s all they sell. I have heard no complaints about the cars that require 87.

  • Juan Rucker

    Horrible me,, I had that itch i was using the incorrect Fuel,. I have a 2007 Audi, which requires Prem/ Super. i have been using Regular for the sake of just being dumb. my car will not start today it’s freezing which i am praying recovers. i will be putting the Fuel boost in on this tank of gas to get it adjusted correctly. and putting in the Correct fuel from now on. it has a tick, but we thought it might be the fan belt. i had to replace a spark plug & coil so far.. but, other then that she’s fine.. clean, and good condition. (well, with hopes she starts today).. Lesson Learned, read the Gas door panel.

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