Tests Counter Slick Claims of Motor Oils

Premium motor oil and fancy additives are nothing more than slick sales, Consumer Reports says.

The consumer watchdog tested 20 types of motor oil under the most grueling conditions--in a fleet of 75 New York City taxicabs--for nearly two years.

The results: There is little difference among brands, as long as the container carries the starburst symbol--a standard set by the American Petroleum Institute for additives needed to keep modern engines running.

The study also found:

* For normal service, changing a car’s oil every 7,500 miles, or at the auto maker’s suggested interval, is sufficient. Although some mechanics recommend oil changes every 3,000 miles, it only wastes money and adds to the nation’s oil disposal problems. Consumer Reports cautions, however, that no oil, synthetic or conventional, should be used for more than 7,500 miles or the maximum interval recommended by the auto maker.

* Expensive synthetic oils worked no better than conventional motor oil in the taxis, which drove 4.5 million miles in stop-and-go traffic. But synthetic oils may be worthwhile for cars in extreme driving conditions: very hot or very cold climates, or in cars with a high engine load.

* Additives such as Slick 50, STP Engine Treatment failed to show a significant reduction in friction and engine wear compared with engines using the same oil without the additives. Consumer Reports said additives are unnecessary as long as the oil used meets the API standard.

* When using a quick-lube center, tell the mechanic what grade of oil the owner’s manual recommends. Consumer Reports found that, unless told, the quick-lube shops failed to use the proper grade about half the time.

Doug Ross, a spokesman for Slick 50, based in Houston, rebutted the magazine’s findings.

“A fleet study like this . . . is so insensitive that there could be massive differences and this test wouldn’t find them,” he said. “We’ve done much more rigorous testing that confirms the benefits of Slick 50.”

The findings are reported in the July issue of the magazine.