The Wax-Ball Recall

Recalls are an old story in the auto industry. Yet the one announced last week by Chrysler Corp. is unique: the first sizable recall in automobile history not for safety reasons but for pollution considerations.* By order of the Environmental Protection Agency, the company must bring back 886,000 1973-model cars and light trucks, fully one-half its production for that year.

The recall is doubly irritating for Chrysler because the part causing the trouble was modified on the assembly line at the insistence of the EPA in the first place. The part, designed by Chrysler engineers, is a sensor containing a ball of wax that softens when engine temperature rises to 60DEG F. The softening frees a valve that recirculates part of the car's exhaust gases through the engine and thereby eliminates some of the harmful nitrogen oxides that are emitted at high temperatures; when the temperature subsides, the wax ball hardens and closes the valve. At first, Chrysler designers placed the wax-ball sensor on the fire wall, a partition that separates the engine from the passenger compartment. There the sensor could measure both engine heat and the temperature of ambient air under the hood. But EPA engineers ordered the sensor moved to the radiator, which gets hotter than the fire wall and provides a better approximation of engine temperature.

Chrysler reluctantly made the move but later found that the wax balls were not softening properly on cars that had been driven for more than 10,000 miles or so. Instead of melting at 60DEG, the wax often was not responding until the engine temperature neared its typical maximum of around 200DEG. The company reported its findings to EPA officials, who promptly ordered the recall.

Chrysler still maintains that the fire wall is the best place for the sensor. But, perhaps significantly, the company has not asked for permission to make the move back from radiator to fire wall. Instead, Chrysler will fit recalled cars free of charge with a redesigned sensor (retail price: $2) still located in the radiator. The new device consists of strips of metal that bend infallibly at 60DEG to open the recirculation valve. In other words, Chrysler has abandoned the whole ball of wax.

*General Motors recalled 2,290 cars and light vans last year because they had been tested for emission requirements at the wrong weights.

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