YONKERS, N.Y.-A grueling test: A fleet of 75 New York City taxicabs driving 4.5 million miles on traffic-jammed streets for nearly two years. The objective: Examine 20 different motor oils to see which perform best.
The verdict: After extensive analysis, Consumer Reports magazine concluded none of the popular brands tested-not even the expensive ones-performed significantly better or worse than any other.
That flies in the face of the millions of advertising dollars spent by oil companies trying to convince motorists that their particular brand of oil can make a car's engine perform better or last longer.
``The surprising truth about motor oils'' was published in July by the Yonkers-based magazine. It stated that as long as an oil container carries the industry's starburst symbol-an indication that the oil contains the full complement of additives needed to keep modern engines running reliably-a motorist can generally buy oil by price and availability.
Consumer Reports found:
Even expensive synthetic oils worked no better than conventional motor oils in the taxi tests. However, based on chemical tests, snythetics are worth considering for extreme driving conditions: high ambient temperatures and high engine load or very cold temperatures.
The taxicab tests suggest that the 3,000-mile oil-change interval commonly recommended by mechanics is too conservative. For ``normal'' service, changing a vehicle's oil every 7,500 miles (or at the automaker's suggested interval) should provide good protection. More frequent oil changes won't hurt a car, but motorists ``could be spending money unnecessarily and adding to the nation's oil-disposal and energy problems.''
The magazine doesn't recommend leaving any oil-synthetic or regular-in an engine for more than 7,500 miles (or more than the maximum drain interval recommended by the vehicle manufacturer). Accumulating contaminants such as solids, acids, fuel and water, could eventually harm the engine. ``What's more,'' it added, ``stretching oil-change intervals might void a new car's warranty.''
Although pricey engine additives-such as Slick 50 engine treatment, STP Engine Treatment and STP Oil Treatment-boast that they reduce friction and engine wear, Consumer Reports said they show no significant differences over engines using the same oil without the additives. It said additives are unnecessary ``if you use an oil with the starburst symbol.''
Unless consumers have a real desire to change their own oil-and have the proper tools, equipment and place to dispose of used oil-they're better off just patronizing a quick-lube shop.
``Use a garage or car dealer to change your oil when you need other work done at the same time,'' the magazine advised. Otherwise, choose among quick-lube centers according to price and service.
And ``if you've been loyal to one brand, you may be surprised to learn that every oil we tested was good at doing what motor oil is supposed to do.''
Each taxicab participating in the tests ``got a carefully rebuilt'' engine. After each ran about 60,000 miles through 10 months of seasonal changes, Consumer Reports researchers disassembled it and measured the wear on the camshaft, valve lifters, and connecting-rod bearings.
``Generally, we noted as much variation between engines using the same oil as between those using different oils,'' the article said. ``Even the engines with the most wear didn't reach a level where we could detect operational problems.''
Oil brands tested included Castrol, Exxon, Shell, Mobil, Quaker State and Valvoline.
In an accompanying article, Consumer Reports sampled a number of quick-lube centers in California, Florida, Illinois and Texas last winter. It found most of them ``can do an adequate job'' and offer relatively fast, economical service.
But it recommended that consumers make sure they tell the center what grade of oil their car needs, because at least half the time the quick-lube shops visited failed to use the recommended viscosity grade. And some did not change the oil filter.