Question: My car, a 1977 station wagon with a catalytic converter, now has more than 100,000 miles on it. Is the catalytic converter still doing what it is supposed to do? How much longer will it function well? What effect does the malfunctioning of a converter have on an engine? And what does all this have to do with air quality?--A.K.E.
Answer: Until very recently, little was known publicly about how well emission systems hold up in cars as they age and accumulate miles. Under federal regulations, emissions systems in cars are supposed to continue to do their job for at least 5 years or 50,000 miles, and auto makers must warrant the key parts of the car that control emissions, including the catalytic converter.
A recent study of emissions conducted by the Auto Club of Southern California had both encouraging and discouraging findings. The cars involved in the study were limited to those that had proper maintenance and computerized engine controls, meaning the cars are among the cleanest-running on the road.
What the Auto Club found was that fewer than 10% of the vehicles tested met the statutory (5 years or 50,000 miles) emission standard. On average, the vehicles exceeded the standard for hydrocarbon emissions by 22% and the standard for oxides of nitrogen by 34%.
The good news was that by 50,000 miles, the deterioration of the emission control systems stabilizes and the engines don't continue to get worse. In the category of hydrocarbons, for example, the deterioration in the emission control system virtually stopped after 60,000 miles. In carbon dioxide, it virtually stopped after 45,000 miles. And in oxides of nitrogen, it stopped after about 40,000 miles.
Incidentally, the cars that failed to meet emission standards came from virtually all manufacturers, domestic and foreign. The study looked at 67 cars; these were owned by club members, two major corporations and rental agencies.
More Serious Problem
Although the test did not include poorly maintained cars, engineering experts at the club acknowledged that emissions in these cars are a more serious problem. It is estimated that if all cars on the road in Southern California met federal standards, hydrocarbon emissions alone would be cut from the 360 tons per day currently spewed into the air, to only 180 tons per day.
"Manufacturers are capable of making clean cars," said Michael R. Appleby, the Auto Club's manager of automotive engineering. "Now, all they have to do is get the cars to meet the standards."
As for your catalytic converter, it is probably still doing its job if your car can pass an emissions test required by the Department of Motor Vehicles. The converter can hold up quite well if only unleaded fuel has been used in the engine. But even a single tankfull of leaded gasoline can ruin a converter.
In addition, a converter can be damaged by a misfiring engine, dieseling, hot flooding and an inoperative choke, among other common problems. If you are the original owner of your car, then you should have a fair idea of how the engine has been treated through the years.
The converter uses platinum to stimulate chemical reactions in the exhaust gases from your engine. The hot gases pass over a large surface area of platinum, which converts the hazardous gases to relatively benign gases. For example, poisonous carbon monoxide gases are converted to carbon dioxide by the addition of oxygen molecules.
It is difficult to say how a malfunctioning converter will affect the performance of your particular car, because all cars are different. Generally, however, a converter that no longer is working increases fuel consumption. And finally, if the converter is no longer doing its job, the effect on the atmosphere is that your car is contributing more than its fair share of that 360 tons of pollution every day.