I have a 2008 BMW 328xi. BMW states that the car MUST use premium grade fuel. However, at the time gas prices shot through the roof, I saw an article in the paper that suggested that maybe premium fuel was not really needed. I then tried regular gas in my BMW and there was no knocking and absolutely no difference in fuel consumption or in performance that I could detect. When gas was at its peak price, I was saving close to a dollar a gallon by buying regular grade fuel instead of premium, which made a huge difference. This is the question: Am I missing something or are car manufacturers scamming us when they specify the use of premium grade fuel?
So the car manufactures and the oil refineries have a conspiracy to get you to buy higher priced gasoline that your car really doesn’t need,I wonder how they decided to split the money up?
Conspiracy theories don’t usually get very far on this Forum.
No, I was not suggesting a conspiracy between car manufacturers and oil companies! The “scam” I am referring to relates to the horsepower race. I assume that use of premium fuel squeezes out a few more horses, but does that matter to the average driver?
I would not consider using the wrong fuel, especially for a car still under factory warranty. Just think how much it could cost you if there is a problem and they test your fuel and find low octane in the tank?
The manufactures want you to have few problems with their car and they want it to perform its best for you. Why would you want something different. For the little difference (at high gas prices the percentage difference in price is even less) why take the risk. You did not buy a cheap car, why cheap out now.You bought a premium car. Expect to pay for premium fuel. When you use regular in a car that is built for premium fuel a knock sensor can and will retard the timing so that the engine does not ping. Fuel economy and power will suffer, it’s more noticeable on some cars than others.
Your car is still under warranty. I would do nothing to risk that. If the manual says ‘required’ and not ‘recommended’, I would use premium. Period.
Horsepower figures are always suspect,in years past I believe the American companies did it more (both up and down).The European standard is to rate in KW maybe more accurate and accuracy regulated. Still don’t see any “scam” related to preminum fuel,sure the companies could be overstating their HP figures,that has always been the case,the situation is better today.
It matters to the specification obsessed driver (does the average driver care about the “horsepower race”) he can look at the brocure and say,“my car has more HP than your car”
Are you sure about the $1 a gallon difference figure? Every where that I’ve seen kept the same $0.20 to $0.30 difference between 87 and 93. That means that relatively speaking, when gas prices were higher, the 93 was more of a bargain than it is now.
If you are going to buy and expensive car and then count pennies on the gas, at the cost of engine life, why not also skip oil changes and such?
What everyone says seems to make sense. However, there are articles being written that say otherwise. These are some excerpts of an article from the New York Times that appeared on August 3, 2008, when regular gas was over $4 per gallon:
"While using gasoline that carried a lower octane rating than the engine required was once a sure path to disaster, that is no longer the case. Nearly all automobiles sold in the United States since the 1990s will happily run on regular-grade 87-octane gasoline without causing engine damage, a benefit of the electronic controls that now manage all engine functions…
Before the switch to fuel injection and computerized controls, engines were subject to damage from prolonged knocking. But today?s engine management systems incorporate electronic knock sensors, which detect the condition and adjust the ignition to stop the problem. As a result, it is almost impossible to hurt a current engine by using 87-octane fuel, industry experts say.
?Modern engines prevent the damage from happening before it starts,? said Patrick Kelly, a fuels analyst with the American Petroleum Institute. ?It wouldn?t impact fuel economy. And it wouldn?t impact the emissions. What it would impact is the performance.?
Specifying premium fuel lets a car manufacturer squeeze out more horsepower. BMW, for example, recommends that all the cars it sells in the United States use premium fuel, but they will run on regular.
?There generally isn?t any harm done to the engine by using lower-octane fuel,? said a BMW spokesman, Thomas Plucinsky. ?Because our engines do have very good forms of knock sensing and are able to deal with lower-octane fuels, you will not have any drivability issues. You will, however, lose some of the performance.?
How much of a loss? Some indication can be found in the peak horsepower numbers Hyundai recently released for its new Genesis sedan. On premium, the 4.6-liter V-8 engine is rated at 375 horsepower. On 87-octane regular, it is 368."
Why does the BMW spokesman say “generally” isn’t any harm done,why does the fuels analyst say “almost impossible” to hurt a current engine?
When the boys come out and say “use 87 octane,guaranteed no engine damage,guaranteed no warranty rejection” then we will have a different situation.
Let me get this straight.
You paid $40k for a fine automobile like a BMW, yet you wanna cheap out on the stuff that runs it?
Sell your BMW off and buy a car that runs on regular normally, like a Civic. 
Why does the price of the car have any relevance to this discussion? 93 octane fuel is not inherently “better” than 87 octane fuel. The only relevant question is whether or not the car can be safely run on 87 octane fuel. By the way, 93 octane is specified for very few cars - BMW specifies 91 octane, but only Sunoco sells 91 octane (because of its “blended” pump). So almost everyone who pays for 93 octane is buying more octane than specified by the car manufacturers. When I was in Canada recently, I found that “high octane” meant 91, not 93 octane.
Chrysler owners used to run unleaded regular gasoline in their 10.5 to 1 compression 383’s until they developed holes through pistons. The car makers are not just making everything up. Some people naturally want to read the instructions and then do something else. Change would be good for some people. Kids used to build car models without following the instructions and nothing fit right. If they ever installed something right, it was an accident. Don’t give your engine accidental results; you won’t like most of them.
The other “sham”. is the price some may charge for a Flex fuel vehicle. Most are already (maybe your BMW) because of that marvelous computer. Many only need to be certified and made fuel system compatible. Heaven forbid you could buy fuel from “any” trash collection business or other enterprising distillery (forget ethanol). Govt. might loose a little road tax and ethanol producers might be seen for what they are; government dependents on public assistance…
The octane rating of a spark ignition engine fuel is the detonation resistance (anti-knock rating) compared to a mixture of iso-octane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. By definition, iso-octane is assigned an octane rating of 100 and heptane is assigned an octane rating of zero. An 87-octane gasoline, for example, possesses the same anti-knock rating of a mixture of 87% (by volume) iso-octane and 13% (by volume) n-heptane. This does not mean, however, that the gasoline actually contains these hydrocarbons in these proportions. It simply means that it has the same detonation resistance as the described mixture.
Octane rating does not relate to the energy content of the fuel (see heating value). It is only a measure of the fuel’s tendency to burn rather than explode.
unchndhart-
When you say that “BMW states that the car MUST use premium grade fuel”, could it really be that they state that a certain octane rating fuel must be used, or that lead free high octane fuel must be used? These are all different statements. In places where lead is not allowed, like the U.S., alcohol is the primary octane raising component. In places like California, most gasoline is actually 10% ethanol. In places like this, 87 octane gas and 91 octane gas are probably the same, and no difference in performance would be noticed, since there is no difference in the fuels. 87 octane fuel has 87 as a minimum, and is probably really 91 or higher. Modern engines cannot accommodate the lead that was used in the past to rise octane rating, primarily due to FI contamination, and most new car manufacturers have restrictions on its use. One really needs to know precisely what BMW says to know what they are trying to accomplish.
I don’t think “most” modern car can run E85 - that requires quite a bit of modification in polymers and programming. I’d hate for someone to try this and damage their car. Could they be easily modified? Yes.
There are other articles that say all kinds of things. If the car says premium required, there are articles that agree with that. Believe the ones you like the best. I recommend premium fuel if your car recommends it. Be happy if you are lucky enough to NOT have to learn from experience. Experience is like evolution, if Natural Selection makes a choice, it usually leads to the extinction of a species. You don’t want to be the one that gets selected to learn from experience. Have you heard of the Darwin awards? They aren’t given out for success.
I should add that using low test fuel in a car designed for high test has two downsides.
First it could damage the engine (just because YOU don’t hear knocking does not mean it is not there) and it will result in lower mileage. Not much lower, but then the extra cost is not much more.
If the guy who wrote that newspaper article is willing to foot the bill for damage to your engine, then I think that you can try his suggestion. After all, I’m sure that he has a degree in automotive engineering, right?
At this point, using the wrong grade of fuel carries potential problems for the car’s owner, but not for someone voicing an opinion in a newspaper. When the newspaper and its writer agree to accept liability for damage caused by following their advice, rather than the car maker’s advice, then it might make sense to experiment with fuel. However, I would not suggest that you hold your breath while waiting for them to pay for repairs to your engine.