Alcohol Boosts the Octane Rating
Question: I understand that under the law, oil companies are allowed to add up to 20% alcohol to gasoline that they sell. My mechanic told me that such alcohol content damages fuel injectors and cautioned me against one particular brand. I have been unsuccessfully trying to determine which brands of gasoline contain alcohol. How can I find out which fuels to avoid? --E.W.J.
Answer: Under federal rules imposed by the Environmental Protection Agency, refiners are permitted to add up to 10% ethanol or 5% methanol, the two most common alcohols used as fuels.
Few refiners add alcohol to their fuel, however, because alcohol is more costly than gasoline. The federal government subsidizes ethanol by waiving 6 cents of the 9-cent federal excise tax. But that hardly offsets the higher cost. Ethanol costs about $1.20 per gallon at wholesale, far higher than the wholesale cost of gasoline.
The key reason refiners add the alcohol is that it boosts the octane rating of the fuel. A 10% ethanol blend adds two to three points to the octane rating of gasoline, but the same octane benefit can be achieved more cheaply through refining methods.
In the early 1980s, several thousand gasoline retailers nationwide were selling alcohol blends. Since then, however, the number is believed to have declined. Under California state law, gasoline retailers are supposed to disclose whether their gasoline contains alcohol.
As for potential damage to your engine, some alcohol blends are safe to use, but others may not be safe. Most of the major auto manufacturers recommend that up to a 10% blend of ethanol is acceptable. Some manufacturers recommend against using any methanol blends, but others say a 5% methanol blend is acceptable. Methanol in high concentration can damage ordinary fuel tanks and other fuel system parts.
Q: I purchased a very expensive two-volume service manual with my 1986 Oldsmobile, intending to do my own diagnosis and repairs. But to diagnose a problem, you must be able to read the codes that are generated by the car’s computer. The manual does not tell how to extract the codes, and I don’t want to buy the expensive adapter that the dealer mechanics use. How can I learn the computer codes? --R.B.
A: General Motors cars are equipped with an on-board computer that detects a wide variety of problems in the fuel system, ignition system, transmission, brakes and a variety of other parts.
When a problem is detected, the computer alerts the driver by flashing a “check engine” light on the dashboard. A dealership mechanic can determine the specific problem from the computer memory with the adapter that you mention.
It is possible, though, to obtain the trouble codes without the adapter, according to GM technical experts. Under the dashboard, directly behind the steering wheel, there is a multi-pin connector. On this connector, you will find a terminal labeled B. If you ground terminal B with the ignition on, the “check engine” light should flash once, pause and then flash twice. That signals a Code 12, which tells you that the diagnostics are working properly. Then, it should signal any other codes stored in the computer memory. After these codes are signaled, the “check engine” light will flash another Code 12 to end the sequence.
After you obtain the trouble code, you can determine what problem it relates to by checking the emissions section of your shop manual.
