The "new-car syndrome" afflicts most Americans. They buy a new car, then sell it or trade it in before it's hit 60,000 miles.

There's certainly nothing wrong with buying a new car often, if that's what you want and your checking account can afford it. But a lot of people sell not because they want a new car, but out of fear that it'll cost more money to keep the old one going than to buy a new one. This is not always sound reasoning. In fact, it can often be a lot cheaper to keep driving your old car than to buy a new one.

After your car reaches middle age and has depreciated, you can drop the expensive fire, theft and collision insurance - which can sometimes cut your insurance premiums by half or more.

Also, by the time your car hits middle age - 50,000 miles, say - you've probably got the note paid off, so your only operating expenses are your lowered insurance (liability only) and maintenance costs.

How much are maintenance costs?They don't have to be excessive. With proper care, most cars are capable of being driven for 100,000 miles without sending you to the poorhouse because of a lot of hefty repair bills.

Cars are kind of like people. The older they get, the more care they need. Negligence - through ignorance or whatever - is the biggest cause of shortened life. If you want to keep your old buggy running as long and cheaply as possible, here's what to do:

Don't ignore it in the beginning when it's new. Read your owner's manual, and shop manual if you have one, and note the maintenance (tuneups, oil changes, air and oil filter replacement) that the maker indicates should be performed, and how often. Do it - all of it - or have it done, at the intervals indicated in the owner's manual. If you never change your oil, you don't really have any right to complain because your engine expired about 50,000 miles before it should.

Make sure brake fluid, coolant, engine oil, transmission fluid, power steering fluid, battery electrolyte and differential oil are all at their proper levels. This means checking coolant, battery and engine oil every time you fill your gas tanks. Transmission and power-steering pump can be checked less frequently, but you still want to keep an eye on them. Once a year is okay on the differential (but look at it occasionally to make sure it's not leaking). Leaks may be caused by nothing more than a broken gasket or loosened bolts - but a leak should be stopped. No oil in the differential (rear end) means no rear end.

Check the belts with the engine off and the key in your pocket. If you grasp a belt midway between its pulleys, you shouldn't get more than half an inch of up-and-down movement - any more and you should tighten the belt. Belts shouldn't be frayed, cracked or glazed on their undrersides. if any are, replace them. Belts should be replaced every two years in any event.

Hoses should not be cracked, brittle, super-spongy or leaking. Replace any that are bad. Replace them every two years also.

Inspect brake pads and shoes for wear every few thousand miles. Also inspect brake lines for damage (corrosion, cracks, leakage). Have anything suspicious checked out by a mechanic.

Take a look under the car every few months to make sure that the hanges that hold the exhaust system to the car aren't severely rusted or broken (replace any that are), and that the rest of the system is in good shape. Don't wait till the muffler falls off to fix it.

By performing the recommended maintenance on your car at the maker's recommended intervals, washing it regularly and applying a coat of wax occasionally, you'll be surprised at how long your car can last, and how good it will look.