When we moved back to the United States about 11 years ago, we bought a Saturn, which I faithfully took to the nearby dealer for every service checkup. Once it was out of warranty, I gradually shifted to an independent mechanic who was more convenient and seemed cheaper.

Then, about four years ago, we sold that car and bought a Mazda. This dealership was so far from our house that I never went there for the required checkups and relied instead on Jack, our local mechanic.

But, especially when the Mazda was under warranty, I had this nagging feeling that I was somehow in the wrong. Was my mechanic giving me the same kind of service as the dealer? Was he missing things? Was I doing my car a disservice by where I serviced it?

Everything seemed to be running fine, but then I would hear stories like the one from a friend who had taken her car to the local mechanic instead of the dealer and he put in the wrong kind of oil. It was a costly mistake. She now goes to the dealer for all servicing.

So I decided to see what I could find out. First, I turned to the National Institute for Automotive Service Excellence, which since 1972 has tested and certified repair and service professionals, including dealers and independent mechanics.

It turns out that I’m not alone in choosing not to go to my dealer, according to Tony Molla, a spokesman for the institute. Seventy percent of car owners go to the independents for what is known as “aftermarket” care while the cars are still under warranty.

That means they drive off the lot and rarely, if ever, return to the dealer.

So my first question is this: If something goes wrong when the car is under warranty, and all of us who abandoned our dealers have to return (tails between our legs) to the dealer, will our warranties be voided?

In most cases, no. The Magnuson-Moss Warranty Act of 1975 — which applies to all sorts of products, not just cars — ensures that except in rare instances, a dealer must honor the warranty.

You do, however, need to be sure that nothing is done to the car that expressly voids the warranty. Some warranties, for instance, may prohibit specific cosmetic changes.

And you want to make sure to keep all service records so that if there is a problem with the car and you need to return to the dealer, you can prove it got regularly serviced.

Most important of all, read your owner’s manual.

Know when your car is still under warranty and what that warranty covers. Otherwise, if something goes wrong within three years after you bought your car — which is the average time a car is covered in full — and if your independent mechanic is unscrupulous or ignorant, you may end up paying a lot of money for something you would have gotten free at the dealer.

Making the choice

So how do you decide? Dealer or independent?

Not surprisingly, the answer to some extent depends on whom you ask.

“I’m a firm believer that you should return to the dealership,” said Robert Atwood, management instructor for the National Automobile Dealers Association. “Parts are installed by rigorously trained technicians. Nobody knows the car better than these technicians.”

Atwood acknowledged that dealers’ initial labor costs were often higher than independents because of steeper overhead, but he argued that the dealers’ greater expertise and state-of-the art equipment meant the repairs would go faster — and in the end cost less.

He also noted that car dealerships had access to daily bulletins sharing information about fixing vehicles.

AutoMD.com, which is owned by U.S. Auto Parts Network, an auto parts supplier, collected data last year from the Bureau of Transportation Statistics, the Federal Highway Administration and the Automotive Aftermarket Industry Association. Car owners who went to dealers for repairs spent an average of $1,209 a year versus $903 for those who used independents.

These included common repairs jobs like brake work, transmission repairs and window replacements.

But Brian Hafer, vice president of AutoMD, said car owners should not look just at the labor costs but at the bottom line. Especially in newer-model cars needing complex repairs, dealers will sometimes have more sophisticated diagnostic equipment than independents.

Also, Molla said, even if you’ve been regularly going to your independent mechanic, if you’re nearing the end of your full-coverage warranty, you might want to go to the dealer to find out if anything is wrong. Then, it will be fixed free before your warranty expires.

But he says he doesn’t think car owners should “assume the mechanic won’t have the knowledge that the dealer has,” he said. “It’s possible the independent repair shop hasn’t invested in the necessary equipment, but not necessarily true.”

Customers, he said, should check if the repair shop has a blue seal of excellence — about 400,000 mechanics nationwide do. That means they’ve passed certain exams and are recertified periodically.

Consumers can find mechanics who are blue seal-certified through the Automotive Service Excellence website, www .ase.com.

Getting the best deal

Whether you choose a dealer or independent, there are ways to try to get the best deal possible. First of all, become informed. Call a few shops, including your dealer and other mechanics, to check prices.

Hafer suggests going to his or other websites to try to diagnose the problem and compare repair costs so you aren’t reduced, as many of us often are, to simply saying, “The car sounds funny.”

And don’t be afraid to negotiate.

Hafer said representatives from his company called 600 dealers and independents for a price quote for a specific repair. When they called back a few weeks later and told the repair shops that they had found a place that offered a lower price, two-thirds of the shops discounted the cost by an average of 14 percent.

And realize that sometimes car-related items are just going to be expensive even when they seem as if they shouldn’t be.