Sensor’s Role Is to Fight Pollution
Question: I have a 1979 Buick Regal with a 3.8 liter, six-cylinder engine. The General Motors maintenance schedule calls for a change of the oxygen sensor every 15,000 miles at a cost of about $80. I was told by two different mechanics (neither works for the dealership) that it is not really necessary. Is it or isn’t it necessary?--M.C.K.
Answer: The recommendation contained in your owner’s manual to change the oxygen sensor is one of the more unusual regulations to grow out of efforts to control air pollution. It was essentially imposed by government regulators who were worried that malfunctioning oxygen sensors could result in additional pollution.
An oxygen sensor measures the oxygen content of the exhaust gases and feeds its data to a central command computer, which then adjusts such things as the electronic fuel injection system and the ignition system. If the oxygen sensor fails, the computer has what is called a default mode, in which it goes to an overly rich fuel mixture. This degrades the fuel economy of the car and causes additional pollution.
The rub is that if the oxygen sensor fails, the central computer should alert you that a problem has occurred by flashing the check engine light on your dashboard. If the diagnostic system is working properly, you have absolutely nothing to gain by routinely changing the oxygen sensor.
Government regulators were apparently worried that motorists would ignore the check engine light or that once they discovered that a bad oxygen sensor would not damage their engine that they would then ignore replacing even defective sensors.
Q: I have a 1987 Lincoln Mark VII with about 25,000 miles on it. My service station recommended replacing the oil with Mobil 1 and changing the Mobil 1 every 25,000 miles. Currently, I change the oil every 3,000 miles. Should I follow the station’s advice? I make frequent long trips to the desert.--D.L.
A: Mobil 1, which is a synthetic oil, is an excellent product, but any advantages it offers may not be right for you. Synthetic oils offer some advantages over organic- or petroleum-based oils in starting a car in extremely cold weather. The oil is capable of flowing more quickly in very cold conditions (near zero).
If you use a synthetic product, many oil experts recommend that you not observe the manufacturer’s suggestion for changing the oil every 25,000 miles. Even though the synthetic oil is more resistant to breaking down than organic oil, it can still become contaminated with dirt and engine byproducts.
Your current routine of changing the oil every 3,000 miles is excellent service for your car.
Q: I have a 1980 Skylark with a rebuilt transmission. When the car sits overnight, the transmission grabs with a hard jerk. After a few miles, it works fine. If you have an answer for me, I will be pleased.--J.P.
A: I always have an answer, but I can’t be sure it will fix your problem. What you describe is a classic case of low transmission fluid. But as you know, GM transmissions produced in that period were notoriously bad and the condition may be more serious.
Check your transmission fluid level. If it is not low and the fluid is clear, you probably have some other problem developing.
