Premium Gas

I had twittered about giving my car premium gas after it passed 100,000 miles, and Christian Montoya emailed me this note which I think you guys might find interesting:

I just wanted to let you know that this is a dangerous thing! The difference between regular, plus and premium gas is the octane rating… 87, 91, and 93 if I remember correctly. Every car has its own rating, and I am going to guess that your car is 87 or 91. A lot of people think that giving a car a higher grade of gas is a way to give it “extra treatment,” but this couldn’t be farther from the truth. The higher octane rating means that the gas *burns hotter*, and if you give an 87 octane car 93 octane gas, you are making the combustion process burn much hotter than what the engine is designed to handle, making the car wear out much faster! If you gave your car premium gas every day it would wear out sooner than expected, and giving it premium gas even one day (like a birthday) is not a present at all. If you want your car to last as long as possible, stick to the octane rating it calls for.

I hope this helps! From a reader (and engineer) to you… no more Premium, okay?

Update: Be sure to check out the comments, a ton of great feedback.

50 replies on “Premium Gas”

  1. Wow, something I didn’t ever realize or even think about. I would sometimes give my car the higher grade doing exactly what you said, giving it the “extra treatment”, but a lesson well learned.

    Thanks Christian!

  2. It goes to show, don’t believe all the drivel they stick all over the pumps. Mobil (in Australia) is the worst, with their dual extra-large “8000 Premium” labels next to every hose with Premium Unleaded.

  3. oh, can I please call bullshit on this one? please?

    IANA Engineer (neither is Christian Montoya), but having worked with & on cars, I’d say this is crap. The octane rating is the *minimum* rating of octane the car needs, ideally – not an absolute or maximum level. In Europe, for example, the mandated ocatane rating of “normal” fuel is higher than that in Australia (95 vs 91, from memory). European cars here should be run on premium, but that’s considered standard in Europe.

    The degree of difference in heat produced by burning a higher octane rated fuel is not that different; metals in the engine have quite a high tolerance. The higher octane rating means that the fuel explodes *sooner*, not *hotter*. This means that you get more fuel efficient – as less fuel is needed for the same amount of power. Most modern cars (i.e. since fuel injection) will adjust the fuel input accordingly.

    However! the net benefit is only 5% or so, so you’d have to look at if you can afford it the difference.

    The other possible advantage is that the premium fuel has been filtered & processed better, so it’s cleaner and overall better for your engine.

  4. Higher octane gas doesn’t burn hotter… it has a higher ignition temp… 87 catches fire at a lower temperature.

    So… a turbo or supercharged engine, or one with a higher compression ratio (all of which raise the temperature in the combustion chamber) can prematurely ignite the gas, causing a condition known as “knocking” –which is bad, hence, higher octane fuel stops the knocking.

  5. Just another addition; from Wikipedia:

    “One of the isomers, 2,2,4-trimethylpentane or isooctane, is of major importance, as it has been selected as the 100 point on the octane rating scale, with n-heptane as the zero point. Octane ratings are ratings used to represent the anti-knock performance of petroleum-based fuels (octane is less likely to prematurely combust under pressure than heptane), given as the percentage of 2,2,4-trimethylpentane in an 2,2,4-trimethylpentane / n-heptane mixture that would have the same performance. It is an important constituent of gasoline.”

  6. Interestingly, Shell Gas Stations — at least here in the Midwest — advertises their high octane gas by by adding a cleaning agent to it… “Actively cleans as you drive,” they say.

    If what Christian said above is true, then I’ve simultaneously cleaned my engine while wearing it down even faster. Dang. I’m glad I’ve not been able to afford the premium stuff for ’bout a year now. ๐Ÿ˜›

  7. Yep. This is true. I read several studies on this. Depending on the quality of your engine, and your driving habits, if you give your car higher octane fuel than it is rated for even once every other month, you can reduce its life by as much as 10%. And it doesn’t get you any extra mileage so you are basically paying more to harm your car.

  8. That’s not quite accurate. The octane rating of a fuel is based on the pressure/temperature required to CAUSE ignition and the rate at which combustion occurs, not the process temperature of combustion. Higher octane fuels require a higher temperature/pressure to ignite, which is why higher performance engines require higher octanes. In high performance high HP engines the higher compressions ratios generate more temp/pressure during the squish phase of a 4cycle engine which would cause lower octane fuels to preignite, AKA: detonation, pinging, etc.
    Using higher octane isn’t hurting the engine. It’s actually making less power though. Higher octanes also burn slower. The bang portion of the 4 cycle engine is spread over a longer time (with high octanes) and an engine that is designed for lower octane will not benefit from the higher compression.
    Remember that this is a dynamic cycle and there are a lot of variables involved. The overall benefit of using higher octane than required (unless you have a way of changing your engines programming to utilize the octane) is the added detergents that gas companies add to premium fuel.

    That’s all.
    -Shawn

  9. Calling bullshit too. Modern cars have engine computers that change the characteristics of engine management based on factors like octane level in gasoline. Your owner’s manual will tell the truth so listen to it…

  10. As well, octane ratings are not standardised across states. So “Super” could be 91 in California but only be considered Premium in Texas. Pay attention to the octane number, not the label.

  11. Is that a ’98 Ferrari? ๐Ÿ™‚ I’ve also heard that higher Octane petroleum burns slower than lower Octane varieties (not just hotter), so you get a more complete burn. I’ve got a Dodge Ram, and it pretty much requires รขโ€ฐยฅ89 Octane. Any less is suicide because of the compression ratio.

  12. Matt, your car isn’t that horribly old. I’d say you’re most likely just fine. Like everyone else has said, the reason why some cars require premium fuel is due to premature ignition (and thus the requirement for hotter ignition temperatures to prevent engine knock.) If your car calls for regular, you will see little difference feeding it premium fuel.

    Even now, cars that require premium gasoline don’t necessarily need it (unless it’s got some terrible engine management;) the car’s ECU should be able to adjust if knock is occurring.

  13. Being a car guy, I gotta call BS too. Sorry Matt. ๐Ÿ™‚

    Higher octane rated gasolines simply compress better prior to ignition. This is ideal for high-performance engines with higher compression ratios. It prevents knocking.

    Putting higher octane gas in a typical engine does nothing – just wastes your money. The gas isn’t “better” in any way for your engine, but it’s not worse either. If your engine is designed for 87 octane, that’s all it can use, so to speak. If you’re not hearing knocking, you’re fine.

    But don’t take my word for it:

    http://en.wikipedia.org/wiki/Octane_rating

    http://auto.howstuffworks.com/question90.htm

  14. Bullshit. Even 93, which in the US is referred to as ‘high octane’ isn’t when you comapre it to fuels in Europe and Australia which are 95/97. With a higher octane rating, you get a cleaner ignition and burn. They are also usually fuels that have been processed better as well and will have less residual after ignition.

    Using a lower octane fuel you are causing a lot more damage

  15. Either way, do some research first. A quick Google for octane confirmed what I had been thinking:

    “Octane is a measure of how well a fuel resists premature combustion, or “knocking.”ย Gasoline with too low an octane rating converts fuel to heat rather than power, making for less efficient fuel usage and reduced engine life.”

    So a higher octane fuel would burn more predictably? I’m not an engineer, but that sounds reasonable to me.

  16. My car is older (94) and i have been told switching from mid to high is good for it.

    I dont know anything about the mechanical-whatsits involved, but she seems very happy on this diet.

  17. It’s true that it’s a waste of money to use premium gas in your car if it doesn’t have a high compression/high powered engine. Age doesn’t really matter… If you want to clean out the engine I’m sure there are fuel additives that you could use, but premium gas just withstands compression better before combustion, as people have already said. I’ve never heard of it doing any damage, but it certainly doesn’t do you any *good*. Something I’m going to keep in mind next time I buy a car is making sure that it doesn’t require premium gas. Back in 2002, when I bought my last car, it wasn’t so big of a big deal. With gas prices where they are now, though? Yikes.

    Also – Europe’s minimum octane rating is generally 91, but that’s RON, which is different from the North American rating system, which is an average of RON and MON (see the Wikipedia link on octane rating above). 87 octane gas in North America (or the US and Canada, at any rate) is approximately equivalent to 91 octane gas in Europe. Of course, generally you don’t see anything below… 93, or 95 over here (in Ireland, any way).

  18. Firstly, it’s important to note the difference between European/Asian mesure of Octane and the US measurment. The US premium (93RON) is equivlent to about 97RON in Europe/Asia.

    Secondly, high Octane petrol doesn’t burn hotter unless your engine knows how to. More modern engines will have sensors that can detect higher Octane petrol, and use that petrol more efficiently (let it burn sooner), but having higher Octane in an engine that expects lower causes no damage whatsoever. Infact, it can only help the engine as “premium” petrol will have some additives as well as the higher octane, which could help clean out your engine and make it run smoother.

    Matt, I think you should mark this article as F.U.D. so other people won’t read it without reading the comments first and take it as fact.

  19. I did this, too, but reading the fine manual helps. give the engine what the manufacturer suggests. This can be premium as with the Maxima we used to own, or it can be good ol’ regular as with our current Accord hybrid (interesting that the Accord, with much more horsepower, gets by just fine with the cheaper gas).

  20. Bottom Line: For economics, you want to use the cheapest (which typically means lower octane content) your car will happily run on without knocking. If you have a fuel injected car made in the last decade the engine management system should be able to adapt to at least a grade lower than your owner’s manual suggests. You give up some performance for cost savings. When you want more performance you can up your octane level and your computer *SHOULD* adjust the engine’s timing, but this won’t happen in 1 tank, the computers don’t move things that quickly. The extra heat generated by running a higher level of octane than necessary is pretty minimal, there are probably many other reasons your engine will die before it becomes factor at all.

    In addition: Almost all “premium” cars suggest “premium” gas, not because they need it, but because people purchasing “premium” cars expect it. Do a little testing and figure out what your car will actually run on, five minutes of knocking from running too low an octane will not kill your car. When you do your test just grab an octane booster and pour it in the tank if you do get knocking, and next time fill up one grade higher.

    Rule of Thumb: High compression, turbo charged, and super charged engines will need a higher octane than a standard naturally aspirated engine.

  21. I’m calling BS on this guy…

    A higher octane rating just means that the fuel is more resistant to autoigniting under pressure, meaning the higher the octane rating, the harder it is to get it to combust without spark.

    The Octane rating has no direct impact on the deflagration (or burn) of the air fuel mixture in the combustion chamber once ignited.

    So, while a fuel with a higher octane rating explodes less easily, that doesn’t necessarily mean that it burns hotter. Some fuel manufacturers routinely make higher octane fuel also a higher grade fuel (by changing the mixture composition) which means that there is more energy per liter, however in the real world, this usually translates into better gas mileage (unless you have a lead foot). Remember, internal combustion engines in cars are designed to handle a pretty wide range of temperatures. The more horsepower it puts out, the more heat it generates. If your engine is rated for 300HP, then that’s how much heat it’s designed to handle. Putting around town or even driving on the freeway doesn’t take 300HP (more like less than 10HP), so in those instances, a higher grade of fuel simply means that you’ll get better gas mileage, and because it’s a higher grade of fuel, you’ll also have less autoignition to worry about.

    For the skinny on Octane see here: http://en.wikipedia.org/wiki/Octane_rating

  22. Oh jeez. The amount of misinformation out there about octane is truly frightening.

    Octane is a measurement of gasoline that tells you how *resistant* to detonation it is.

    -It doesn’t mean that it burns hotter (or colder).
    -It doesn’t mean that it has more power (or less power).

    Think of the 4 stroke cycle. You have 4 main phases:
    1. Input – Gas and air are drawn into the cylinder as the piston goes down.
    2. Compression – The piston goes up, compressing the fuel/air mix.
    3. Detonation – The plug fires and ignites the fuel/air mix, causing it to expand and push the piston back down.
    4. Output – The exhaust is vented out of the cylinder.

    The octane makes a difference in both steps 2 and 3.

    You see, when you fire the plug makes a big difference. Ideally, you fire it just before the piston reaches full compression. This makes the shockwave of the detonation hit the piston just as it reaches the top of the stroke, thus giving you maximum power as it pushes the piston all the way back down. Fire too late, and you lose some of the power of the gas. Fire too soon, and you are fighting against the detonation for a short time (in extreme circumstances, this damages things due to the excessive pressure).

    A spark plug is not the only thing that can make the fuel/air mixture detonate. Heat can do it, as can excessive compression. If the mix detonates too early because of one of these reasons, then it’s called “pre-ignition” and it can be very, very bad. In more minor cases, you get knocking or pinging or what have you. These are bad as well.

    Higher octane fuels can be compressed more and they can withstand more heat.

    So for any given engine, it has a certain amount of compression that it uses and a certain heat that it reaches. The octane of the fuel relates to these two factors, and is what’s given in your car’s manual as the octane of gas that you should use.

    Using a higher octane won’t hurt anything, because modern cars are computer controlled, and they can adjust the timing of the spark so as to ignite at the right time for a range of octanes. Basically they can allow for different levels compression at detonation by adjusting the timing.

    However, using a higher octane *won’t actually buy you anything* with these cars. The car’s computer can adjust and compensate for different octane levels, but it does not give you any more power, as such. You get basically the same amount of power from the higher octane than you do from the lower ones.

    It is possible to modify the engine in minor ways so that you do get more power from higher octane gas, but such a modification changes the compression or air/fuel mixture, in such a way that it will *require* the higher octane gas.

    In short, use the minimum octane that does not cause pinging, which would be what the manual for your car says to use. It will run fine on that and not gain anything from higher octane gas without modification.

  23. Most car engines have a knock sensor that will retard the timing if the engine pings/knocks/pre-ignites/call it what you will. As smart as you would like to think your engine is they won’t Advance the timing if you put better fuel in them though.

    So using a higher octane fuel will give you zero performance increase or fuel efficency bonus. You would need to have your ECU remapped or some kind of piggyback computer alter the fuel injection mapping. If you have a carburretor’d engine you could adjust the jetting to get the benifit.

    It will not damage your engine though. Using a lower rated fuel then your engine is desinged for will decrease peformance/efficiency though as the knock sensor retards timing.

  24. You should put the grade of fuel in that the manf says you should. You’re not doing the car any favours going higher. Going lower is asking for trouble but higher just asks the computer to compensate resulting in nothing beneficial.

    And this is assuming that you believe the rating on the pump. *That* is what I call BS on. And double for those silly stickers that say how the company only makes 2% from each $1. The companies spike the fuel with nasty bits to reach their ratings (and perhaps to unload some toxic waste).

    I’m cranky today since I have to run 91 minimum and now that is the maximum I can find anymore. Since the moment that happened I’m certain that the 91 is lower quality. And when we had a shortage and they were allowed to spike the fuel with more garbage my car has been unhappy. I”m getting a crappy car next time so I don’t have to worry.

  25. This isn’t true. The octane rating has to do with how fast it burns, not how hot. Different cars need different gas because the pistons need to be pushed slower or faster. If the gas burns too fast the piston wont get pushed all the way. If the gas burns to slow the piston will be still getting pushed when it doesn’t have anywhere to go. All that said, you still shouldn’t use Premium gas if that’s not what your car was made for.

  26. I looked at the date on this post and thought you were having a bit of April Fool fun. Personally I am getting obscessed about who is looking at my blog. (See latest self mocking post).

  27. Sorry.. but I have to agree. That warning is utter rubbish, especially for cars less than 15 years old. Utter drivel.

    Not to mention you often get better gas millage with higher octane fuels

  28. I’ve always just added whatever the car said to use. In my old taurus – it took 87 – and ran great – even at 200,000+ miles – but if you put in 93 – it ran bad… In my 4 cylinder 1989 ford mustang – if you put 93 octane in it – it would barely start… Now in my Audi – if you don’t put in 93 or at least 91 – it runs horrible. In fact it is so picky as to even the brand that it burns.

  29. I too call BS on most of the replies.

    The person who got it all down right, and explains it well too, is Otto.

    Premium gas has a higher octane that’s it. It is not filtered more. It does not clean your engine better (even standard fuels have detergents in them.) In some cars it will give you slightly better mileage but very rarely enough to justify the added cost.

    Its a little thing called marketing, the gas companies can make 15 cents more a gal on something that costs them 5 cents more a gal to make. Cause there are suckers out there that believe all the BS that they fling round.

  30. Don MacAskill has it right; if your car doesn’t require Premium, using it is a waste of money.

    Nik Cubrilovic’s post is incomplete; the last words should read “but only if your car requires a higher-octane fuel.”

    I didn’t read further, because those two summed up the responses you got – facts and crap, respectively.

  31. I am an owner of 30 years old car, but I’d like to add my $ 0.02 to the discussion here, all from personal experience:)

    ***

    The car I have is built in 1977 – 3 decades ago. It’s still 50’000 km total mileage, as we use it quite rarely. Engine is 1200 cc (1.2 l) – less than 60 horsepower, I think. Recommended octane – 93 (or 95).

    If that matters, I am in Europe:)

    The rated maximum speed of the car is 140 km/h (kilometres per hour). I’ve tested that:) Used fuel in the experiment: octane 93.

    Now, I once tried fuel with octane 98. The car reached 150 km/h (same road)! So the higher-grade octane actually gives you more power.

    Notes:

    1) The card reached 150 km/h and was able to hold that speed for a couple of minutes, no problems.
    2) After that nothing bad happened, except that the engine started to overheat (anti-freeze liquid temperature gauge reached the red zone, which means over 100 degress C!) and it was wise to slow down for a while – what I did.

    Conclusion:

    Giving your car higher octane fuel gives some more power to the engine. Maybe not much, 5% or so, but the results are obvious.

    I doubt that it worked because the car was old. New engines should be able to use this excess of power even better than old ones.

    So it’s quite safe to give your car 98/99 octane fuel, in case it needs 93/95.

    But! I wouldn’t recommend that for long time. Because every engine is adjusted to a typical octane number. Higher than recommended could wear it off maybe a tiny bit faster than it should. So ride your car happily, give it higher octane for its birthday, and don’t worry:)))

    ***

    Afterword:

    I am a bicycle rider, I ride everywhere all year round, and I am happy I do not have to use a car often.

    I reached the 17’000 km milestone recently and I am proud of it:)

    But it’s nice to remember there’s the whole large world of cars out there, and that once I was part of it:)))

    Cheers:)

  32. Yes that is BS, using too low an octane rating will damage your engne, too high is just a waste of money.

    Also as Weiran already poitned out, North America uses a different way of calculating octane rating so there is a difference of 4 for equivalent fuel. 87 and 91 in north-America is the same as 91 and 95 (respectively) in the rest of the world.

  33. Interesting is that here, in The Netherlands, normal gas is 95 octane, and premium is 98, or even higher.

  34. note about my claim of better millage – that’s from my experience with my car (a ’97 VW Jetta) I get about 3+ mpg better, saving me more money than the gas cost.

    YMMV… no pun intended.

  35. Premuim is ok to run to clean an eninge. As the higher octane will burn hotter and can help clean the engine. Though this should not be a normal procedure, just if things are starting to wear.
    On the new HEMI engines they can run on 87 on 91, 91 gives optimum power though 87 is fine.

    A higher octane fuel will NOT get you better gas mileage niether. Use what your car is meant to run on. Engines are built different & have different compression ratios that help determine what the octane should be. I highly doubt a power advantage is noticeable hile running 93 octane in an 87 engine. I’ve used octane booster before and it was not noticeable. Only thing is if you were towing. Also remember it is hard to tell if your really getting better mileage either way. So many things can affect your gas consumption. Hitting the brake, hitting the gas more, maybe heavy winds creating drag, catching more red light, rougher roads, etc. So it is uncontrollable the little things that could make one tank seem to get better mileage than another.

  36. Using a higher octane will not harm your car.

    When cars were running Leaded fuel the fuels had a RON of 96.

    Standard unleaded only had a rating 91 RON. Therefor many models dropped power with the forced introduction of unleaded fuel.

    The RON rating is the fuels resistance to detonate (explode). The higher the RON, the higher you can compress the fuel (ie with a turbo or supercharger) or advance the timing without causing the engine to PING.

    Pinging is what will destroy your engine.

    Cars that can’t adjust their timing for higher octane fuel will gain little benefit from it, so its probably a waste of money.

    However modern cars with O2 sensors in their exhaust can make mild gains from using a Premium Fuel.

    If you like the idea of using Premium fuel.. go for it. if you’re looking to save some cash at the pump… use the minimum octane rating your engine is designed for.

  37. I ride a 2006 Harley Davidson FXDLI (1450 cc AIR COOLED)in Las Vegas . Last week the temperature was 116 degrees F.I run 100 octane fuel in the hot months here.I was riding with a friend on a hot day (He has an ’07 H.D.air cooled). I could hear the pinging over the noise of my bike. I asked him about it, he said he was going to take it back to the dealer for repair. I asked him what type of fuel he was burning,he said he was using off brand regular.I suggested giving some name brand premium a try,he did,away went the pings I looked so smart!! I recently had a problem with my bike, the H.D. dealer came out to trailer it to the shop and the driver smelled the racing fuel and told me I was going to burn it up!! “that’s like running jet fuel in it”.Jet fuel is Kerosene with stuff in it to keep it from gelling. Ignorance is bliss!! I kept my mouth shut. Octane is the resistance to pre-ignition thats all!!!

  38. See this website for a general explanation on the octane debate:
    http://www.cartalk.com/content/features/premium/questions.html

    Additionally, All things being equal, the only thing which determines the fuels ability to provide energy (I am not talking about a particular type of engine’s mechanical ability to make the best use of this energy) is the amount of carbon atoms per molecule of gas. This explains why a different gas such as ethanol doesn’t provide the same power or mpg as good ol’ gasoline. See article below (for example):

    http://aaae.okstate.edu/proceedings/2005/Articles/556.pdf

    There are no unbiased, independently tested and scientifically proven additives to gasoline that improve a gas’s energy output. Octane does not increase the potential energy in the fuel because it is not a fuel.

    So, if you really wanted to “scientifically” test how
    octane ratings affect power, mpg, etc. (if at all) you must use two identical cars or one car with all the fuel drained between tanks of gas. Each car(or the one car) must then be subject to the exact same driving conditions using the different octane fuels. A good device I found for monitoring fuel consumption is the ScanGauge. Plugs into any car with an OBD2 port and tells you instantaneous fuel consumption and average fuel consumption.
    Better yet, to reduce any possible variables between gas types, fill up using regular gas (always from the same station), add an off the shelf octane booster and then measure fuel consumption. Heck, if you can, stick the car(s) on a dyno and measure the bhp. Using these methods are the only way to test if higher octane gives better mileage or more power.
    Anything anyone else says is only anecdotal.

    Does using the wrong octane cause your engine to wear more quickly??? It really doesn’t matter because the wear is so insignificant the rest of the car will probably wear out before the engine does.
    James

  39. I suprised after reading all the responses no one seens to know that under full throttle acceleration higher octane gas let’s the timing stay advanced higher and let’s the engine pull harder (not talking low compression 4 bangers). There is no interference from the computer concerning pollution under WOT, although that may change in a few years. It’s documented fact a V6 Accord has a 10 hp difference between 87 and 93 octane. Granted you really have to know your car to notice that difference but when that guy is trying to keep me from getting on the freeway before him I want it.

  40. My 2008 Passat 2.0t wagon says it needs premium. On the first fill up I inadvertently put in regular. It didn’t seem to notice the difference and, outside of the guilt I felt, seems none the worse for wear. Did I hurt this wonderful little car or can I continue to put in reg. Reg. sure helps the wallet.

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