How do you answer this question when you are at the gas station? Is premium gasoline really better for my car? What's the difference anyway? Answer: octane levels.
The octane level
The octane level indicates what is the antiknock value of a particular gasoline. The knock (or detonation) happens when the fuel ignites at the wrong time or too quickly due to an overheated combustion chamber. Imagine a short-fuse firecracker. It could blast in your fingers before you have time to throw it. That's about what can happen inside an engine, and the pistons will be damaged. So additives are mixed in with the gasoline to control its combustion, and to increase its antiknock value. To determine the octane level of a certain gasoline we compare a sample of it with a sample of a reference gasoline called octane – or iso-octane – which has a very low rate of detonation and a given value of 100. Gasoline is generally classified as follows:
- "Regular" at 87
- "Medium" at 89
- "Premium" at 91 or more
What about fuel economy?
In a high-powered or turbocharged engine (mostly found in sports cars) the gasoline injected in the cylinders is put under intense pressure and temperature. With a low octane level, the gasoline may ignite early and cause a vibration that generates a metallic sound called "ping." We must prevent this spontaneous combustion of the gas-air mixture to happen before the spark is produced by the sparkplug, because this could damage the engine. In this instance we have to use a fuel with a higher octane level ("premium," that is an octane level of 91 or more).
Most cars come with engines designed to run on "regular" gasoline (octane level 87). These engines do not compress the gas-air mixture as much as the high-powered engines. So it serves no purpose to fill up our car with "premium" when the engine does not require it, since it is the fuel's heating attributes (combustion heat), and not its octane level, that determines its power efficiency.
What about fuel economy?
Fuel consumption is determined by a number of factors: low-pressured tires, wind factor, outside temperature, remote starters, and most of all wild accelerations! Also a lot of people believe that gasing up with "premium" will give them more mileage per fuelling. Here's what Petro-Canada has to say about this on its Web site:
"Gasolines with higher heating values give better fuel economy than those with lower heating values. There is generally only a small difference, about 2%, between premium and regular gasoline. This difference traditionally favours premium gasoline but it can be in either direction."
The possibility then to get more power out of a "premium" gas is very low. The higher price is not worth it.
Somebody say "Engine cleaning?"
Among the types of additives put in gasoline there is the detergent type whose purpose is to clean the combustion chamber, the injectors, and the valves in order to prevent overconsumption of fuel and reduce the amount of pollutants in exhaust smoke. This is where the oil industry has to rely on its advertising. Oil companies will try to sell you their "premium" gasoline at a premium price by boasting its cleaning qualities! But all major oil companies add detergents to all their types of gasoline, even "regular" (check their ads). So will they tell you that there is more detergent in "premium?" Maybe they will, but you should know that modern engines built with electronic fuel-injection offer remarkable performances, better combustion due to an accurate mixture ratio in the fuel injectors, and electronic ignition allowing the gas-air mixture to ignite at the exact time. If you add to this a multitude of sensors controling everything, you then get an engine with a clean combustion. Detergents are good but an overdose of them is not necessary.
My conclusion
Check with the car maker's recommendations, you may find them written near the gas cap or in the driver's manual. A high octane level will have no incidence on cold weather starts, idling, and fuel consumption. So rest assured that as long as you are not driving a high performance roadster, the only gasoline your car will ever require is "regular" with an octane level of 87. And, which is the best oil company? I say without any hesitation "the cheapest!"