The High Octane Truth About Gas
By: Grant W. RepsherAll about octane
Which fuel is best?
Upgrade, or downgrade?
Alternative fuel: Ethanol
Alternative fuel: DieselAfter oil change intervals, gasoline grades (Regular, Mid-Grade, and Premium) are about the most widely misinterpreted automotive concept -- and for good reason. When gas was still selling for a buck or so a gallon, ratings didn't receive that much press. At today's prices, however, there is a renewed interest and financial incentive in finding out which fuel is best to burn.
Each gasoline grade is associated with an octane rating, which you'll see on those yellow stickers at the pump. In North America, regular gas is equivalent to an octane rating of 87; mid-grade with 89; and premium with 91. In some states, particularly those with a higher elevation, you may find what's sometimes called an "Economy" grade, which is lower than 87. At the other end of the spectrum, you'll often see premium gas with an octane rating as high as 95, depending on the gas company you get your fuel from.
What purpose do octane ratings serve? In short, they measure the fuel's resistance to detonation, or the premature ignition of the fuel/air mixture during the engine's compression cycle. Marketing on the part of the oil companies and auto manufacturers has perpetuated the notion of octane ratings, which are classified by the Research Octane Number (RON) or the Motor Octane Number (MON). Both measure the fuel's resistance to detonation, but the MON measures the engine under load (i.e. towing) and so is roughly 10 points lower than the RON. RON is the measure found across Europe, while North America uses an average of RON and MON.
This detonation is also known as "knocking" -- an annoying and, in the short term, largely harmless condition of reduced efficiency and power. The operative word here is "was," because with the adoption of modern fuel injection; engine knock sensors (generally after 1984); and unleaded fuels (1988), these timing/fuel related issues have essentially been alleviated in new vehicles.
Some Gen Xer's will remember the Exxon Tiger anti-knock campaigns touting their premium fuel's ability to "Drive your engine clean." Today, though, fuel standards governed by the EPA, FTC and the state offices of weights and measures, require that all fuels -- including regular -- contain sufficient additives to prevent carbon buildup and protect your vehicle's engine, injectors, etc. Additionally, all gasolines (with the exception of E85 ethanol or other flex fuels) contain the same amount of latent energy, premium fuels simply have been "reformed" to have more compounds removed and/or additives added.
Somewhat illogically, these additives actually make the fuel harder to burn, meaning they may help avoid the premature ignition in high compression and turbo/super charged engines.
The oil companies and refineries are a very influential bunch and have spent millions of dollars convincing both the automotive industry and consumer that there needs to be different "levels" (or qualities) of gasoline available for purchase. Car manufacturers have obliged by producing some high performance/high compression engines that require higher octane fuel to achieve their highest marketed horsepower ratings. In other words, you can't get that 255 horsepower you see advertised on TV without Premium fuel.
Meanwhile, the oil companies figure they can use this "need" for Premium fuel as an excuse to peddle it to anybody who will pay. The fact is, though, that Premium fuel isn't necessarily the most efficient for even that "255 horsepower" car.
So what's the magic number? The absolute best advice when considering which fuel to use is to consult your owner's manual. The manufacturer has designed the engine to perform optimally with a specific fuel rating in mind, which will provide the maximum efficiency and power.
Can you use mid-grade or premium fuel in your engine, which is rated for regular? Yes, but it will be a waste of money. Even though the oil companies might try to make you believe otherwise, your car will not run cleaner, more efficiently or produce any additional power.
Can you use regular gas in your vehicle even though the manufacturer specifies mid-grade or premium? Yes, you can but your engine will not perform in its most efficient range and over a prolonged period, you risk the possibility of engine damage. The additional few bucks you spend per tank-full will likely outweigh the money you save by running a fuel that provides less fuel efficiency. Also some manufacturers have even tried to void warranties in claims where evidence shows that improper fuel was used.
One consolation is that at today's prices, the margin of premium over regular has fallen, meaning it is cheaper in relative terms to opt for the premium.
Knock, Knock: When to Deviate from the Manufacturer's Claim
When to "upgrade"
If your fuel-injected vehicle is experiencing detonation (knocking), it may be a sign of some mechanical problem like faulty spark, carbon build-up, tainted gas, etc… If you or your mechanic has explored all these possibilities however, and you still have the problem, you may want to try bumping up a grade. This may happen with high mileage cars or during considerable periods of load, like towing, for example.
When to "downgrade"
Just because fuel prices have ballooned to four bucks a gallon is still no reason to automatically default to regular fuel. However, due to the additional additives found in premium grades, you may occasionally experience difficulty starting your engine, particularly during the winter months. An especially cold engine (i.e. winter) doesn't contain enough heat to immediately ignite this fuel, at least until it has warmed up some. If you experience rough starting or feelings/sounds that your engine is not running on all cylinders during and just after cold month startups, you may want to consider regular fuel while the snow flies and switching back to the "good" stuff in the spring.
The use of ethanol (ethyl alcohol, the same as in your Martini) as a motor fuel has recently received a shot in the arm with the rapid escalation of average gasoline prices in North America, not to mention the apparent increase in meteorological activity associated with the effects of global warming and the political/military campaigns throughout the middle east.
Ethanol is attractive first because it is a renewable resource that can be produced from organic matter like switchgrass, sugarcane, and, of course, corn. Additionally, this fuel proves much better for the environment due to reduced hydrocarbon, benzene and carbon dioxide (CO2) emissions. While the "side-effects" of this fuel source are limited, there are, as always, a couple of catches. The US currently consumes over 320 million gallons of gas every day, which equals roughly 3,700 per second, only about 40% of which is produced domestically. Even if we were to convert the lion's share of our existing agricultural resources to some sort of ethanol production, we would still only satiate a small percentage of the growing demand.
Also, ethanol doesn't hold quite as much energy as does the equivalent amount of straight alcohol, meaning consumers may see a decrease in mileage with the use of this fuel. Finally, because ethanol production is still a growing agricultural industry, it is subject to farming subsidies making it a political pawn, especially with the size and clout of the petroleum industry.
Currently, many states use ethanol as an additive in the gasoline supply, which goes (typically) unnoticed by drivers as the ethanol mixture represents only about 10-15% of the fuel. The average vehicle can utilize this fuel without any modification or noticeable decrease in performance. E85 however, is the inverse in that the fuel is made of 85% ethanol with the balance being unleaded petrol and other additives. Currently, there are only a few hundred filling stations offering E85 nationwide.
Auto manufacturers have been producing "flex fuel" vehicles for the last several years that are designed to run efficiently on both regular gasoline or the E85 blend. Only recently, with the renewed interest in alternative fuels have they marketed the vehicles uniquely or even informed their owners of the flex fuel capabilities.
The US uses approximately 15 billion gallons of ethanol in its fuel supply annually, which accounts for about 12% of fuel sales.
Diesel - The Black Sheep in the Fuel Family
Diesel fuel, named after its inventor, German engineer Rudolf Diesel, like gasoline is refined from crude oil. Diesel represents roughly 20% of US fuel consumption, which equates to about 56 billion gallons per year.
Diesel fuel is particularly popular in industrial application for its high-energy and torque (load moving) properties. One gallon of diesel contains about 147,000 BTUs vs. 125,000 BTUs for gasoline. In addition to being more efficient than a gasoline engine, diesels fewer and slower moving parts make them considerably more durable. Therefore, nearly all buses, semi-trucks, farm equipment, heavy machinery, ships, trains and construction equipment employ diesel engines.
Diesels have somewhat of a tainted reputation with American drivers and are remembered as being smoky, noisy, and difficult to operate in cold temperatures. Also, the exhaust and emissions from diesel engines is known to cause both smog and cancer. Yet, while diesels make up only a few percent of automotive sales in the US, they are very popular for passenger cars across the globe and have even gained renewed interest in North America, especially with the adoption of new diesel standards, which lower the sulfur content and go into effect in mid 2006.
This, new emission technologies and the widespread introduction of common rail and other direct injection fuel systems will likely lead to a significant improvement in diesel performance and subsequent resurgence in the US over the next few years.
Grant W. Repsher is the founder of Servassist Online. He is a writer with Automotive News, the auto industry's premier trade publication, and a former contributing editor with the AIADA (American International Automobile Dealers Association). To contact Grant about this article or to suggest future topics, please click here.
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