I bought my first car at age 14. By the time I turned 15 and got a learner's permit, we--the car and I--had accumulated some 200 miles up and down my parents' driveway. I also had accumulated a decent box of tools and was learning how everything on the car worked.

I was, and still am, a gearhead--obsessed with automobiles. In the past 50 years, I've worked on hundreds of cars. I've restored a dozen British and American classics, built engines and transmissions, and taught automotive theory.

And I've seen the industry change. Gone, for the most part, are the days of the cluttered, dirty garage with old parts on the floor, dim lighting, and mechanics who wipe their hands with oil-soaked rags. Those mechanics have been replaced by a new breed trained in electrical theory and mechanical and computer systems. Now called "technicians," they generally work in clean, well-lit shops.

The National Institute for Automotive Service Excellence gives exams in more than 40 specialties, and good mechanics aim to be ASE-certified in a number of automotive systems. ASE master certification is considered the gold standard.

Most auto technicians are honest and hard-working. Some aren't. The world of auto repair is still susceptible to incompetence and scams. The volume of complaints to federal, state, and consumer-protection organizations suggests that unnecessary or faulty repairs cost consumers millions of dollars annually. Finding a shop you can trust--see our list of recommended garages on page 135--is the best way to avoid wasting money on a car. What follows is my advice on preventing bad experiences.

Oil Change Every 3,000 Miles?

Many people believe they should change their car's oil every 3,000 miles. In my opinion, it's one of the biggest myths in the auto-repair industry.

The last time cars needed to have such frequent oil changes was in the early 1970s, before clean fuels, computer controls, and more sophisticated engines and oil chemistry.

Don't take my word for it--trust the engineers who designed your car. They know more than anyone else who services it, and they wrote into your owner's manual the actual oil-change requirements. Most cars can safely run 7,000 miles or more before an oil change; some makes and models can go up to 15,000. Many vehicles have sensors and software that will monitor your driving conditions, such as long distances versus stop-and-go traffic, and tell you when to change your oil.

In an effort to reduce pollution from waste oil, the state of California has created a website (checkyournumber.org) that gives manufacturers' recommended oil-change intervals.

Well over 30 brands of oil additives are for sale in stores and on the Internet. They claim to give a car greater fuel economy, longer engine life, more power, lower emissions, and smoother operation. Don't waste your money. No manufacturer recommends additives, and using them can void the warranty. Carmakers have spent billions on sophisticated fuel delivery and other technologies to achieve reliability and performance.