Running On Regular: Do Premium Vehicles Really Need Premium Gasoline?
Long before gasoline rocketed through $4 a gallon many people were dismayed to see a significant percentage of their income disappearing into the tank of their car. Today, a wobbly economic outlook, increases in the cost of most other forms of energy, as well as the cost of life’s staples, have prompted folks to look for every possible way to cut back on spending. “Can I save money by running my car on Regular?” “Will it hurt the engine?” my friends ask. More than one person driving a car the manufacturer has spec’d for Premium has told me “I use Regular and my car runs fine.” Are there consequences of “down grading” your fuel? It is definitely a timely question, so we sent e-mail inquiries off to a half dozen manufacturers asking about their technology and their policy on the matter.
While waiting for their reply let’s review some internal combustion engine characteristics. Fuel does not truly explode in a cylinder, at least it isn’t supposed to. It burns smoothly, albeit very rapidly, across the cylinder. The octane rating is a measure of the propensity a given fuel has to burning, rather than exploding. Gasoline “exploding” in the cylinder is frequently called “detonation” or more colloquially, “knocking” or “pinging”. These explosions, because they happen as the piston is rising during the compression stroke and try to shove the piston back down the bore, can do damage over time. In the case of severely stressed motors, such as in race cars, a few seconds of serious detonation can destroy the engine. Two of the mechanical considerations affecting how smoothly a fuel burns are compression and cylinder head configuration. Two variable considerations of great importance are the temperature in the cylinder and the ignition timing. Every manufacturer designs and builds their engines to operate most efficiently for the application intended with a gasoline of a particular octane rating.
Not all that long ago, before the advent of engine management systems, the result of tanking up a high compression vehicle with standard grade fuel was immediately obvious. Providing the stereo wasn’t cranked up past 100 decibels, the pinging or knocking from the engine compartment let you know something was not right. Driving up a hill, towing a load or simply accelerating quickly produced an unnerving rattle from under the hood. It sounded very much like your carbureted V-8 had morphed into a diesel. Until the age of microprocessors enabled the creation of engine management systems, the consequence of a steady diet of low octane fuel could be fatal for a high performance engine.
General Motors, Honda, Toyota and BMW responded to our inquiry. Honda’s public relations representative declined to comment on the issue. Toyota noted that essentially all their current models are designed to run on 87 octane. I asked about using 85 octane, available in some markets, and Bill Kwong of Toyota corporate PR told me they would run fine, with maybe only a slight 2-3 percent decline in horsepower and fuel mileage. But 85 octane is usually only offered in markets at altitude (i.e. Denver, Colorado) where the reduced oxygen doesn’t allow an engine to reach full designed power in any event. If you drive a modern Toyota, the octane rating of your fuel isn’t much of an issue. But what about a brand aimed squarely at the performance market? What about BMW?
Thomas Plucinsky, BMW Product and Technology Communications Manager told us all BMW engines are designed to run on 91 octane. All performance testing, including EPA emissions and fuel mileage, is done with 91 octane. However, though BMW is all about performance, their motors will run on 89 or 87 octane without damage. The knock sensors pull the ignition timing back and eliminate detonation. There will be a loss of power and a decrease in fuel mileage, but the size of the horsepower loss and the increase in fuel consumption depends upon many factors, such as ambient temperature, exact formulation of the fuel and driving technique, so BMW does not offer any estimates for operation on lower grade fuels. One not so obvious concern, Mr. Plucinsky noted, is the type and quality of additives the gasoline companies include in the fuel. Premium gasolines may have better additive packages which are more effective keeping fuel systems (particularly injectors) clean and working efficiently, than those in regular grade fuels or off-brand products. Using lower octane or off-brand fuel could be degrading the fuel system over time, setting you up for a repair bill down the line.
Dave Muscaro, Director of Engine Development/Calibration for GM power trains explained GM has “three flavors” of fuel specification for their offerings: Regular (87 octane) Recommended, Premium (91) Recommended, and Premium Required. Again, we are more concerned with the last two categories where regular could be substituted for the specified Premium. All the engines have a knock sensing ability that retards the spark when detonation occurs. For the premium recommended vehicles the spark advance will be pulled back enough to eliminate the detected knocking. The typical driver will not notice a performance decrease, except under load, and mileage will decline slightly. The engines intended for performance, such as the LS7 or the supercharged small block V-8, are Premium Required powertrains. The customers clearly were not primarily concerned with economy when they chose a performance vehicle and GM optimizes the engine management system to deliver the highest possible power output at all times. To this end the detonation control system does not retard the spark to the point required to prevent all knocking. It would seem a determined deranged drag racer could run Regular in his Corvette and, over time, he might manage to melt a piston or two.
If burning 87 octane in your car, when 91 octane is specified, will not harm the engine, and the performance degradation is not noticeable in typical driving, how much money can you save? The Energy Information Administration, U.S. Government Department of Energy, offers some figures for US gasoline retail prices (these are averages, all areas, all formulations). A year ago Regular was going for $2.982 a gallon and Premium was commanding $3.196 a gallon. The 21.4 cent difference delivered a 6.7 percent saving over Premium. This June 23, 2008, Regular extracted $4.079 from your wallet while Premium sucked up $4.312 for every gallon. The differential (23.3 cents) has grown slightly since 2007 but buying Regular is now only 5.4 percent cheaper than Premium. Since 5 percent is roughly the typical percentage of mileage decrease to be expected with the 87 octane fuel in a 91 octane engine, is there any savings at all?
Bottom Line: Most modern engines are fuel injected and controlled by sophisticated engine management systems which can rapidly and accurately compensate for lower octane fuel by retarding the ignition. Running these cars on 87 octane will not hurt them. However, the immediate savings at the pump may be wiped out by the subsequent drop in fuel mileage and performance, not to mention the possibility of damage over time.
Comments
Reilly Brennan
Great piece, Stan. I think I've heard this question about a dozen times in the last few weeks as well.
Trinks
Agreed, excellent piece. One question though: was there any word on running Premium in an application that calls for Regular? Most knowledgeable people I've talked to say there should be no difference and no risk of damage, but there's also a lot of misinformation out there and it could be relevant for folks who needlessly fill up on the good stuff.
fantasyfreddy
Even if you have an older car that "must" run on premium, you can probably put in 1/2 premium and 1/2 regular and that should make it run smooth while saving a little cash.
Reilly Brennan
If that's possible, yes. My understanding of gas pumps is that once you select the kind of gasoline you want you are sort of locked into that. If you change the fuel type you have to do another sale. Not a huge deal, but it makes this difficult(er).
Anonymous
What your referring to is called midgrade, and mixing premium and regular gas is exactly what most gas pumps do to make it.
Truck Accessories
I have an old Lexus V8 (1990) that I bought right before gas prices topped 2 dollars per gallon. Since I'm out of love with this particular car, I decided to go with 87 octane each and every time and haven't had a single problem over the course of 6 months or so. With any luck, I'll be able to keep saving 20 cents per gallon until the car dies entirely and I get some transportation more suited to this economic climate.
John F
Here is a link to a Car and Driver article where they actually measured performance differences of regular v. premium. You'll see that the results are varied and sometimes non-existent. My guess would be that humans could not perceive even the largest difference in performance without a stopwatch. See: http://www.caranddriver.com/reviews/hot_lists/high_performance/features_...
I'm skeptical about a loss of fuel mileage using regular. For example, ethanol is a quick and easy way to raise octane but ethanol has less energy/gallon that gasoline. I have a GM premium recommended car with 108,000 miles and I get much better than (old) EPA MPG ratings using regular.
Here in IL you can use 89 octane which is just a blend of regular (87) and premium (91) instead of mixing the two grades.
z-man
what a lot of people don't know, is that most modern vehicles will run fine on any octane rating. example: a camaro z28 with the LS1 engine can run on any octane. it will get the best mileage on any octane. however, it will not get the most POWER out of lower octane.
the ECU retards the spark for lower octane on most vehicles. so if you want to pay less at the pump and don't care about the 12 hp you lose, by 87 instead of 91.
the only vehicles that can't handle a change like that are vehicles with carbs, and most of those are motorcycles, atv's, and ancient cars.
also, any engine that is not designed to run with ethanol will get less mpg, less power, and increased emissions with anything from e10 to e85. e85 vehicles will get less mpg, less power, and more emissions if they use normal gasoline.
we're all being tricked.
Mena
I fail to see the point of lowering your recommended octane rating just to save a few bucks. I'd rather not take the chance of ruining my engine just to save, in my case, $3 a week in gas. Have you ever melted a piston before? New engines plus the labor to install them (no rebuilds for melted pistons) cost significantly more than the pitiful $156 dollars a year I'd save by running 87. If you guys want to save money, buy one less Starbucks coffee a week. The savings is the same and you don't run the risk of damaging your engine.
Those of you in hot desert climates best stick to the recommended stuff. Your engines are working harder in those climates and you need all the detonation resistance you can get.
Stan Baldwin
Good comments, all. I'll address two points we didn't spend as much time on as maybe some folks would have liked: 1) the impact of driving technique on mileage and 2) when running a higher octane fuel than the manufacturer calls for makes sense.
We mentioned the importance of load on the detonation issue. As the gentleman from GM told us, if someone were to run regular in their LS7 and drive like they had a raw egg between their right foot and the accelerator pedal, they would never notice the difference. Of course, why they heck would someone buy a Corvette and drive it like a Prius? Yeah, yeah, I have seen those guys suffering from midlife something or other that apparently think the mere image of themselves in Corvette will enhance their libido but real drivers are looking to use that awesome perfomance. If you prefer to drive for fuel mileage, buy a vehicle that is intended to deliver high mileage.
Be that as it may, how you drive has a huge affect on the fuel mileage you experience. We built and ran a LS1 Camaro at Bonneville last year (Street legal class) and were able to consistently click off 20+ miles per gallon on the highway. Put your foot into the modified GM V8 and 14 miles per gallon was also possible. As I tried to emphasize, manufacturers design engines to do what they intend as efficiently as possible. There is no subterfuge here. If the engine is most efficient running 91 octane it will be less efficient on 87 octane, period! the amount of degradation will depend, to some extent, upon the design characteristics, but much more on how the driver operates the vehicle. It's not politics, it's physics. For the record, I'm with folks like reader Mena, the small savings in initial expense does not come close to justifying the loss in performance and mileage, or the increase in potential problems.
Now as to burning the good stuff when it may not be specifiec: I like the comment made under Seyth's Question of the Day; Reilly buys his car premium when he feels good. Anthropomorphizing our cars is nothing new and many a good story has been created around vehicles with names (mostly female it should be noted), but most of the time the extra octane is not a benefit. However, the conditions we noted in the original piece can make a higher octane the best fuel for the situation. Heavy Load and High Temperature increase the need for a fuel which will not easily detonate. Member Mena notes in his comment to Seyth's question that he runs premium when towing during the summer - smart fellow. That is a strategy that will not only protect the engine but provide more of the power towing requires. As many of you know, here's what happens when a modern engine compensates for detonation: the ignition advance is reduced so the fuel burns later in the compression stroke. Power is reduced, and because there is less power at a given throttle opening, more throttle is required (decline in fuel mileage). Engines designed to run on regular will protect themselves in the same way as the hi-po versions, so they too sacrifice power for longevity if knocking is detected. Putting in a load of 91 octane under these circumstance allows the engine management system to keep the spark advance at full range and the engine happily putting out full power.
Another related experience at Bonneville last September shows how even racing engines can sometimes benefit from higher octane than the originally intended fuel. Our Camaro was designed and tuned for 91 octane (wanted it to be easily streetable). Though initially the onboard computer was set with a fixed fuel map determined by dyno runs at roughly sea level, we knew that the altitude of Bonneville needed to be addressed by either developing new maps for the conditions or allowing the engine management system to make the adjustments on the fly. So we put the Mass Air Flow sensor back in and set the air/fuel ratio at 12.7 to 1, dropping 20 horsepower at the wheels. Our first runs showed good performance but it was clear the heat and the extreme load was causing the engine to pull the spark a bit. A short trip over to the fuel supplier and we had a few gallons of 104 octane to to feed the Camaro. The difference on the following runs was subtle but noticeable. The engine management program was able to leave the tweaked LS1 at full advance.
Thanks for all the comments! Keep the shiny side up!
J Bain
Very interesting article and comments. What are your thoughts about the fact that octane (at least in Canada) is boosted simply by adding a moderate percentage of ethanol? Yes the alcohol boosts octane, but as an earlier comment suggests, there is also less energy contained in a gallon of ethanol than in a gallon of gasoline. That should mean less performance and gas mileage.
Good reading! Keep it up.
FJ Owner
Thanks for the article, Stan. I beg to differ with Toyota's response to your inquiry, though. The manual of my '07 FJ Cruiser clearly says to use Premium. Whether or not that's actually necessary, I still don't know.
Stan Baldwin
Ahh, you need to read my "fine print". I wrote that "essentially all" Toyota's specify regular. You happen to own the only one that calls for premium. And there is a bit of a mystery here because the driveline of your FJ is identical to that of the Tacoma... which does not call for the 91 octane juice. My Toyota contact did not know the reason for that one. Thanks for making an interesting point.
PilotJimL
Our Toyota Prius manual said use a "premium" fuel. That sounded odd to to me for a gas-saver, so I dug deeper into the manual. I found that it should use 87 RON+MON/2 fuel, i.e. "regular." I suspect that the translation should have been "quality" gas, not "premium" which we Americans equate to 91-93 octane.
Jorge
Stan , great writing ! As a technician for Audi , i get the question of fuel quality/octane rating, asked all the time! What most folks don't seem to understand is that climate [i work and live Dallas TX] ,driving habits, as well as vehicle maintenance are all factors when it comes to mileage. What will be come interesting to see is ,as most manufacturers are going towards direct injection [as is Audi/VW] these engines will have high static compression and require the use of prem octane fuels.
I guess some folks need to realize that if you are going to get the mileage and or performance that was specified originally by that manufacturer, you have to run the fuel that is reccommended on the fuel door or in the owners manual {good god,do people even read those any more!} Thanks
Someguy
I liked the article, explained the question they were trying to address, explained how these engines work, and then asked the companies, i think its pretty interesting how honest the companies were, and i like the fact that they all included information about the additives in premium. And the conclusion was excellent, yes u can run a non-recommended fuel, but why do that if its going to handicap the reason u bought the car in the first place. I drive an E46 BMW and that is what i think about everytime i fill up. it is a 2000 and 8 years later though the electronics may be getting a bit dated, the engine runs the same as when it was manufactured.
Great Article!
Robert Baldwin
Stan, this is the best explanation of this issue I've seen in print. Have you considered sending it to all the major newspapers, perhaps offering it for a few $$? The amount of idiocy and misinformation in the general media on automotive issues remains staggerng, despite the correct technical info being readily available.
btw, there are a couple of other low-volume cars where the owner really needs to buy premium - e.g. Mazdaspeed 3/6. That specifies 93. 91 will work, but the ECU is hearing knock and pulling timing. There's one cylinder is these engines whose piston in rare cases fails, taking out the engine with it. The root cause hasn't been published, but the knock that occurs before the ECU can fix it might, just might, cause small defects in a piston to become cracks and you know what happens next. Using 87 will trigger a limp mode which will protect the engine, but power is dramatically reduced. I suspect that some other mechanically supercharged cars (rather than turbo, where the ECU can regulate boost) may have a like issue.
Stan Baldwin
On the matter of adding alcohol to boost octane. For those who might find it of further interest, back in March I wrote a piece, "Can E85 Make Motorsports More Environmentally Friendly?, that was aimed more at discussing the reality of running E85 to cure the world's ills, than performance issues. But in there were some observations about how the fuel behaves in a competition engine. Here's a section from that article:
Normal
0
How about the practical matter of building competitive
machines? As noted earlier ethanol has
some useful attributes when it comes to making horsepower. With a stoichiometric (ideal) air/fuel ratio
of 9 : 1 it is possible to make more horsepower with ethanol than gasoline
(14.7 : 1) from a given engine displacement.
However there are a number of disadvantages to be considered. At nine parts air to one part ethanol, fuel
mileage with ethanol is some 30% less than with gasoline. The lower boiling point and lower vapor
pressure contribute to starting difficulties and potential vapor lock in
carbureted systems. As you certainly
remember from your last cocktail party ethanol is eminently compatible with
water. Unfortunately water decreases
the power output of E85 and increases the corrosive action. Ethanol tends to separate from gasoline,
especially at lower temperatures where it is also most likely to absorb water,
further degrading the combustion characteristics. Dealing with E85 poses problems.
Fritz Kayl, founder and president of Katech in Clinton
Township, Michigan builds the engines for the Corvettes running the American Le
Mans Series. He noted though “there is
not a whole lot different” in the E85 engines, there are issues. Seals susceptible to alcohol are a concern
but can be addressed with the proper materials. As to corrosion, many engine components are not yet specifically
certified for use with E85 so Katech has acquired important proprietary
information developing the motors for the ALMS Corvettes. The greater fuel consumption means the cars
experience a greater change in weight from full to empty, especially in long
distance events, which affects handling.
Choosing the right materials for fuel tank through exhaust requires an
understanding of chemistry and a flush bank account. However, the single biggest problem is knowing what E85 blend is
in the tank. As noted earlier simply
saying you are running E85 is not enough information to set up a car. Tuning the cars for the specific blend is
critical to making horsepower and achieving reliability. With decades of Chevrolet “bowtie racing”
experience Katech is confident E85 will not slow the factory Corvettes in the
slightest.
Thanks once again for all the comments.
BillyBlastoff
Here in Iowa ethanol is subsidized by the State. Premium and midgrade fuels cost less than 87 octane unleaded. My Crossfire calls for premium and I run premium. My gal's SUV calls for 87 octane but for ten cents a gallon less I pump the mid-grade.
H. Gerken
Regarding fuel octane & detonation. Flex Fuel vehicles have to be designed to run on the lowest octane desired by manufacturer,that being gasoline. It would seem ethanol being a higher octane could use a higher compression ratio & more timing advance to have peak performance & efficency. Dual fueled vehicles will only be efficent on one fuel.
Brian-one day I'll own a Ferrari!
This is a great article, it really caught my eye since I drive a BMW and have recently starting using 87 octane fuel. Based on this article I will be sitching back to prem. asap. Thanks so much for the article!!
John F
Stan: As you can see from my earlier comment, I'm a skeptic. Has anyone tested major brands' gasolines to see if an octane difference even exists? When gas was $1.00/gallon, each grade cost $0.10 more than the lower grade. That same $0.10/grade differential exists today with gas over $4.00/gallon. Thanks. John
Stan Baldwin
Hmmmm John F. I'll surmise you are suggesting all three grades of gas available at your local Arco, Chevron, Valero or Rotten Robbie's are basically the same with maybe just a dye added to make them look different? I'm not a conspiracy advocate, but in this case there are simply too many people watching. The octane rating offered at the pump is supported by laboratory testing that verifies the combustion characteristics. Manufacturers, such as BMW, have made substantial investments in time and money to assure fuels that will be burned in their engines will first and foremost deliver the experience their customers expect, and secondly, not damage the hardware they spent an even larger amount of time and money creating. Unless one might be persuaded that manufacturers could be getting checks in the mail from oil companies paying them for specifying premium fuel when there isn't any real difference across the grades, why would car builders bother with such convoluted devious behavior?
The point noted, that the cost differential between grades hasn't changed much since gas set you back $1/gallon, should be less of a conundrum. The price of basic oil has climbed massively. The differential cost of the processing and additives to create premium over regular (for instance) has moved about 10%. Sorta like the cost of beef in a hamburger going up 200% and the price of the cheese popping 10%. That slider is now $2 but the cheese version is only 40 cents more, rather than the 35 it was two years ago. (Please don 't rake me over the metaphorical coals on actual hamburger costs.)
One last observation on performance (including mileage) between regular and premium fuels. The performance difference (if any) depends hugely upon the design of the engine and how much of the potential performance the driver attempts to access. A full race motor, if it were for some inexplicable reason designed to tolerate lower octane fuel, would suffer a significant drop in maximum power when burning regular gas. A production motor is much more likely to be designed to tolerate the kind of insociant behavior modern vehicle operators are likely to inflict these days. With such an engine the driver may not notice the drop in performance, and the drive train management system carefully protects itself and soldiers on. That doesn't mean there is no difference, it simply means the operator is unable to detect the difference. Ever consider the fact that NASCAR drivers can tell when the right rear tire pressure is down a pound but the guy next to you in rush hour traffic hasn't noticed his right rear is darned near flat? It's a matter of operator sophistication.
Good stuff John, Thanks for raising the issues.
gregdollar
I know this is a little off the wall but will you tell me how much gas on average is in this single hoses pumps my sportster only holds 2.2 gal of fuel if I don't give the first gal away or carry a can she seems not as responsive.
Greg
John F
Stan: Good thoughts. Thanks for the great article and the feedback. John
Bryce M
Stan,
Fantastic article, loved it. I drive a 2004 Honda S2000 and I would never ever run anything but premium in it. Even though the fuel door and manual says recommended, I just know that I would be pumping in a death sentence by using 87 octane. Higher compression ratios of newer high performance engines definitely need 91 or higher (wish I could get 93 in AZ...) and I will only use gasoline from certain companies i.e. Chevron and Shell. The additives do make a difference. your engine will be healthier and run longer and better.
Thanks again for the great article.
Bryce
Anonymous
Thank you Stan for the great summary that clearly addressed all of my questions. I'll stay with the premium, knowing it might prolong the life of my car!
Anonymous
The mention of the technology that will sense that a lower octane gasoline is being used and adjust the burn of the fuel accordingly is interesting; however, I can't find a post where it mentions WHEN this technology became available. I drive a 2000 BMW Z3 Roadster and was wondering if this auto had such technology.
Stan Baldwin
Simple answer - your Z3 most definitely has the capability. Anti-knock technology was introduced a couple decades ago and has evolved as microprocessor and sensor technology has evolved. Each manufacturer has delivered their solution to the matter, and be assured BMW does not lag when it comes to automotive technology.
BMW owner
Great article on a long debated topic. A good conclusion, especially those of us who want to enjoy the performance of our vehicles for a long time.
Pay now or pay later.
Post new comment