Jasper
9-10-04, 12:56 AM
From carconnection.com:
About once every two weeks, my wife informs me that "the car is broken," meaning that the Low Fuel light is on. I must then perform the manly task of filling the gas tank (after all, she does all the cooking). I usually use the discount station adjacent to my shop, because it's very convenient. I do not concern myself with brand names and I use regular unleaded in our cars.
So what do you need to know about gasoline?
Most stations sell three grades or "octanes" of gasoline. "Regular," typically 87 octane, is the cheapest, still running you less than $1.90 a gallon in most of the country (sorry, California ). "Plus" is the middle grade, 89-octane gas, costing well over $2 per gallon, and "Premium," 93 octane at the station I use but maybe 94 octane at the brand-name stations, can cost up to $2.50 a gallon.
What's the difference? Why is there a difference? And which should you use?
First, an oversimplified explanation of engine operation. Gasoline and air are drawn into the cylinders and compressed (squeezed) as the piston pushes up. At the proper time, the spark plug ignites the compressed fuel-and-air mixture, which burns (not explodes). The expanding gas drives the pistons down, producing power. As the fuel-air mixture is being compressed, it may get hot enough to ignite on its own, resulting in pre-ignition, which can cause a rattling or pinging noise from the engine, a reduction in power, and in extreme conditions, engine damage. The octane rating of a gasoline is its resistance to pre-ignition.
Most cars and trucks sold in the U.S. are designed for and run well on regular gas. If your car or truck runs fine on regular, increasing the octane will not improve your car's performance, and may in fact cause problems with cold starting and performance, because of another often-ignored factor called volatility. Volatility is the ability of a liquid to mix or atomize into the air. Gasoline will not burn until it has atomized into the air, and atomizing into cool and cold air is much more difficult than warm.
There is an inverse relationship between octane and volatility. The higher the octane, the lower the volatility. Many mysterious hard-starting and cold-drivability problems are attributed by car manufacturers to volatility. Refiners adjust the volatility of fuel from summer to winter, but they cannot control all factors, such as temperature and humidity. Also, regional emissions requirements may affect fuel volatility. Often an early cold snap can cause a wave of cold-engine problems, until the fuel blend catches up with the weather.
Never pay a penny more than you have to for gasoline. If your car runs well on regular, or pings just a little, stay with regular. If your car begins to ping continuously, have it checked by a mechanic who specializes in engine performance. If everything checks out, go up one grade on octane. Unless you are driving a car with a high-performance engine, or a truck pulling a very heavy load, you shouldn't need premium, and if you do, you probably have an undiagnosed problem. Also try periodically switching back to regular in case your ping was a temporary condition.
About once every two weeks, my wife informs me that "the car is broken," meaning that the Low Fuel light is on. I must then perform the manly task of filling the gas tank (after all, she does all the cooking). I usually use the discount station adjacent to my shop, because it's very convenient. I do not concern myself with brand names and I use regular unleaded in our cars.
So what do you need to know about gasoline?
Most stations sell three grades or "octanes" of gasoline. "Regular," typically 87 octane, is the cheapest, still running you less than $1.90 a gallon in most of the country (sorry, California ). "Plus" is the middle grade, 89-octane gas, costing well over $2 per gallon, and "Premium," 93 octane at the station I use but maybe 94 octane at the brand-name stations, can cost up to $2.50 a gallon.
What's the difference? Why is there a difference? And which should you use?
First, an oversimplified explanation of engine operation. Gasoline and air are drawn into the cylinders and compressed (squeezed) as the piston pushes up. At the proper time, the spark plug ignites the compressed fuel-and-air mixture, which burns (not explodes). The expanding gas drives the pistons down, producing power. As the fuel-air mixture is being compressed, it may get hot enough to ignite on its own, resulting in pre-ignition, which can cause a rattling or pinging noise from the engine, a reduction in power, and in extreme conditions, engine damage. The octane rating of a gasoline is its resistance to pre-ignition.
Most cars and trucks sold in the U.S. are designed for and run well on regular gas. If your car or truck runs fine on regular, increasing the octane will not improve your car's performance, and may in fact cause problems with cold starting and performance, because of another often-ignored factor called volatility. Volatility is the ability of a liquid to mix or atomize into the air. Gasoline will not burn until it has atomized into the air, and atomizing into cool and cold air is much more difficult than warm.
There is an inverse relationship between octane and volatility. The higher the octane, the lower the volatility. Many mysterious hard-starting and cold-drivability problems are attributed by car manufacturers to volatility. Refiners adjust the volatility of fuel from summer to winter, but they cannot control all factors, such as temperature and humidity. Also, regional emissions requirements may affect fuel volatility. Often an early cold snap can cause a wave of cold-engine problems, until the fuel blend catches up with the weather.
Never pay a penny more than you have to for gasoline. If your car runs well on regular, or pings just a little, stay with regular. If your car begins to ping continuously, have it checked by a mechanic who specializes in engine performance. If everything checks out, go up one grade on octane. Unless you are driving a car with a high-performance engine, or a truck pulling a very heavy load, you shouldn't need premium, and if you do, you probably have an undiagnosed problem. Also try periodically switching back to regular in case your ping was a temporary condition.