NEW CARS

SWEDISH cab driver James Bergkvist says he's driven his 1982 Saab 900 Turbo more than 620,000 miles - that's about 25 trips around the globe. Not too many people are going to get that kind of mileage out of their car. But they could learn something from Mr. Bergkvist. He says the secret of his car's longitivity is regular maintenance, naturally - and something as simple as oil changes. Frequent oil changes, every 6,000 miles or so.

How often do you change the oil in your car? Every 3,000 miles? Every 6,000? 10,000? Never?

Some people never take the time for this 15-minute, $15 operation, perhaps because they plan to get cash in their car at 25,000 or 30,000 miles and buy a new one. They may have no problem while they own the car, but who's going to want to buy it and hope to run it another 30,000 or 40,000 miles?

Results of the neglect are bound to show up, in the form of engine wear. Some experts suggest an oil change as often as every 3,000 miles, with an oil filter change at 6,000.

Your automobile communicates with you in clunks, wheezes, buzzes, and screeches. To get the best out of your car, pay attention to what it's telling you. ``Ignoring your car's warning signals can be costly,'' advises the Highway Users Federation. But during this age of self-service gas stations, vehicle maintenance is too often neglected.

In the beginning of this section, the Monitor takes a look at the new-model cars from Detroit and beyond. And whether you wind up buying a new car or just want to get the most mileage out of your old one a series of stories that follows will help you understand the language of your car.

There is basic upkeep advice such as taking care of your tires and buying a battery, some help in finding a good auto-body shop - and for those who like to putter under the hood, pointers on buying the right auto parts.