A friend recently sent me a link to a Marketplace episode which purported to show that there was an oil company conspiracy afoot to get us to use the highest priced, highest octane or "premium" gas in our ordinary vehicles rather than the lowest priced, lowest octane gas which is all we ever need in our cars. Let me preface the following by stating that I am poor and cheap, so I would truly love to see a good argument for only using the lowest octane gas. If I ever find that argument, I will never again buy the mid grade (middle octane level). Unfortunately, I haven't found that argument yet.
First of all, the Marketplace show starts, and runs throughout, by raising a false dichotomy between regular (lowest octane) gas and premium (highest octane gas). This is known as the "straw man" or "false dragon" fallacy. They have found a case of some idiot (I have no doubt there are millions of such idiots), who asks a gas-jockey what gas to use in her normal car and he dishonestly tries to sell her the most expensive grade (I have no doubt there are many thousands of such gas-jockeys). The rest of the show then purports to try to prove that you shouldn't waste your money buying the highest octane gas for the average car. I have been driving and buying gas for decades and I have not personally come across any argument or sales pitch by the oil companies, or anyone else, which has ever suggested we should be using the highest octane level in any but the costliest, high end vehicles. Thus, the entire Marketplace show, in perfect line with their generalized "Let's expose another Great Conspiracy weekly." format, fails to have any real value except for those who will believe any sales pitch, from any unqualified source, and who always assume that more expensive means better, a loosely defined group that I have always described as foolish. The question they should have asked, and tried to find answers to, is not: "Do I need the highest available octane level in my gas?" but rather: "Which of the three available octane levels causes my car to run at optimum performance?"
Secondly, for the sake of argument, let's take their efforts at face value. The only thing these video-bloggers have proved is that they understand (or care) very little about the scientific method and that evidence-based critical thinking is not a significant part of their arguments. They find an "expert" who is willing to claim that lower octane levels are better. This is a very unscientific appeal to authority. What has he based his opinion on? He never mentions any studies; he simply says "Trust me, I'm an expert." Do all such experts have the same opinion? Does ANY other expert have the same opinion? Marketplace never says. Knowing Marketplace, I suspect they omitted talking about that because it might ruin their show. They set up an "experiment" (please note that I did not say a "scientific experiment") in which they use a car, with no given specifications (uncontrolled), to yield a result of precisely 1 data point for regular gas and 1 data point for premium gas. This test, even if it were valid, would yield nothing more than a single anecdotal testimonial, something that is great for convincing a gullible public, but is essentially meaningless as scientific evidence. Once again, however, let's proceed as if it were an acceptable scientific test. The result of their test was a savings in gas when the HIGHER octane level was used, meaning that the car ran more efficiently and suffered less engine stress in overcoming friction to drive the car the test distance, USING THE HIGHER OCTANE LEVEL. Their conclusion was, to paraphrase: "Never mind the evidence, just take my word for it in spite of the evidence." Sound much like the climate-change denialists? As I stated above, this was not a scientific test and was essentially meaningless as a basis upon which to draw a conclusion, but what would they have said if the result had been reversed with 4.8 l/km for the lowest octane gas and 5.0 l/km for the highest octane gas. Would they have said, "Never mind the evidence." then? I don't think so. If they agree that the result is meaningless no matter what the result is, then why have the test as part of the show. The only possible answer is that this kind of pseudo-scientific crap works on the average joe who is either too ignorant or just too intellectually lazy to really examine what they are watching. Result: lots of soap-flakes sold by the advertisers to a burgeoning populace of Great Conspiracy theorists.
Back to reality: I will repeat that I have never personally come across any argument or advertisement which suggests that we should be using the highest octane level in our car. But neither have I ever seen any proper argument presented for using the very lowest octane level available. What I have heard from the oil companies and from a large number of so-called "experts" on television, in the Toronto Globe and Mail, and on the internet, is that: a) if you are driving an old beater (i.e. a somewhat worn-out engine, especially an older model with less efficiency wary computer controls "on-the'fly") then use regular gas as a higher octane level will not overcome the inefficiencies present to any noticeable degree; b) if you are using a newer model, high-efficiency vehicle, like a top end sports car, then use the highest octane level because those engines are designed for use with such gas and run most efficiently when using such gas; c) if you are running a newer model vehicle with the engine still in reasonably good running shape, then use the middle grade gas, or regular gas with an octane additive, as the higher octane level helps the engine to run at optimum efficiency, yielding better gas milage and less wear and tear on the engine.
It is true, as they pointed out in the Marketplace show, that modern cars are equipped with knock sensors (small piezo-electric microphones) which send a signal to the engine control unit, which in turn retards the ignition timing when premature detonation (causing engine knock) is detected. According to everything I can find on the internet, retarding the ignition timing reduces the tendency of the fuel-air mixture to detonate, but also reduces power output and fuel efficiency. It is simply easier on the engine (and easier means greater output and efficiency) when a slightly higher octane reading is used, especially when using higher loads, hotter (e.g. summer) temperatures and at higher elevations (such as in Edmonton). If I was running my car in Toronto especially during the winter and when hauling a lighter load, there would be a lesser need for boosting the octane rating slightly than if I was running it in Edmonton, especially during the summer or when hauling a greater load.
Everything I can find, including write-ups by independents, suggests I should be using the mid-grade gas until the engine is quite old and worn out. I will happily buy the cheapest gas if anyone can point out a good, scientifically backed argument for doing so. Maybe the studies disproving the (vastly) majority view are there on the internet and I simply haven't found them yet. By all means, please send the links to me if anyone finds them.
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