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  Mechanical Feature

Which Should I Choose?

Posted 3/26/2004
By Alexis Gross

No matter who manufactured a part you install in a car, at the end of the day, the name on that job is yours. You work hard to do the best repair possible for your customers, and you don't want a parts failure to be a reflection on the quality of service you provide.

The best way to avoid this dilemma is to use the right part in the first place. But which parts are better for the cars you repair: aftermarket or original equipment manufacturer (OEM)?

"It depends on the type of work being done," said Guy Garrett, training and membership coordinator for ASA-Ohio and an ASE master tech. "With any type of emissions or driveability part such as a PCV valve, fuel injector, fuel pump, onboard computer components, control modules or sensors, almost all higher-end quality shops try to put in OEM parts whenever they can. If you put in an aftermarket part, it just may not run right. They're not designed to run with those parts."

Don Seyfer, owner of Seyfer Automotive in Wheat Ridge, Colo., agrees that OEM is the way to go with emissions- and driveability-related parts, but pointed out that in many cases, mechanical parts from the aftermarket are often a better value than those from an OEM.

"With things such as brake shoes, clutches, exhaust parts and seals, I think the aftermarket is superior in availability, guarantee and pricing," he said. "A lot of the aftermarket parts I use have a limited lifetime warranty, and that's a good selling point. The OEM parts typically only have a one-year warranty."

Location can also determine what type of parts shop owners use for a repair, simply because only certain parts are easily available.

"I'm rural and I don't have a big selection of OEM parts stores," said Denny Mandeville, owner of Canyon Automotive Repair & Service in Sedona, Ariz. "The closest one is in the next town over, and that's an hour round trip."

Reliability is Mandeville's biggest concern when choosing a part for a repair because both his reputation and his profits are on the line.

"When I first started in this business, diagnosis was 15 percent to 20 percent of your total ticket time and repair was 80 percent of the time," he said. "In the past 15 years, there's been a complete reversal. I used to use aftermarket throttle position sensors. If the car came back exhibiting the same symptoms, I had no choice but to do a complete diagnosis to find out I had a bad part, which I was not reimbursed for, nor were my technicians. If I used an OEM part, I'd put it in once and it generally didn't fail again.

"I've had this issue with various parts manufacturers who've said, 'Our parts have gotten much better.' Well you know what? I'm never going to find out because once burned, twice shy. If you're losing three times the bay rate on a redo and not getting reimbursed for it, you're going to go back to a part you know has proven reliability."

So why are emissions- and driveability-related parts causing such a problem for these shop owners?

"My personal experience is that aftermarket emission control parts do not seem to give the same reliability," said Mandeville. "They seem to have a higher failure rate and more warranty issues than OEM parts do. I've never had an issue with aftermarket mechanical parts vs. OEM."

According to Garrett, Mandeville's perception of the differences between aftermarket and OEM in this area is correct.

"They're just not built the same," Garrett said. "A lot of internal circuitry doesn't always match exactly. For example, when I was doing technical training for Snap-on Tools, we took an AC Delco control module for a late-model GM and cut it in half. We also took one from an aftermarket supplier and cut it in half. Two of the circuits that help control the timing advance curve and spark control weren't even there. They had one big generic circuit that covered everything.

"By doing that, the parts supplier didn't have to cover as many part numbers. But it wasn't the right part for the car and the part number in their catalog said it was. That's a huge problem, especially when you get into these areas that have emissions programs, because then you get a car that may not even pass the emissions standards."

Not all differences can be detected by cutting a part open, either. Garrett used spark plugs as an example.

"You've got to get an OEM part for those," he said. "You may have a plug that physically looks the same; the problem is the heat ranges don't match properly. If you get a spark plug that is too hot for that application, it retains too much heat in the combustion chamber and that is probably the No. 1 cause of NOX failures in Ohio right now - the wrong spark plugs. And they're not the wrong ones! If you go to the book, it's the right number, but it's a cheap aftermarket part. It's got too wide a heat range on it and it runs too hot."

Garrett stressed that you need not avoid all aftermarket parts for certain emissions and driveability applications. However, he said, you want to get a quality name brand if you're going to get an aftermarket part.

Garrett, Seyfer and Mandeville all agreed that most educated shop owners are aware of these differences.

"By educated, I mean the progressive shop owners; those who have attended Automotive Management Institute (AMI) classes and go to seminars and workshops," said Seyfer.

The biggest problem, said Mandeville, is ignorance.

"We don't know what we don't know," he said. "There are people who try their darndest, but if they don't know what they don't know, how are they going to fix that?"

Mandeville and Garrett both agreed their use of aftermarket driveability- and emissions-related parts has decreased in the past five years, in part because of the differences between the two parts, but for financial reasons as well.

"A lot of aftermarket parts suppliers are selling the OEM stuff and getting a little more competitive on the pricing," said Garrett. "AC Delco's done a great job with that. They've got a big aftermarket program where they'll discount the pricing on it and give pretty good service with a lot of perks, and you can buy their OEM stuff a little more reasonably priced."

In the end, no matter what deals you're getting or who you're affiliated with, it all comes back to whose name is at the top of that repair order.

"A lot of the aftermarket suppliers are really great to work with, and they'll just bend over backwards to help you. But I'm not going to put a part into someone's car that I don't think should be there out of loyalty to a parts supplier," Garrett said. "All you've got left when it's all said and done is your reputation, and if you're going to compromise that for monetary reasons, I think you're making a grave mistake."

Alexis Gross is a communications assistant for the Automotive Service Association (ASA) and is a regular contributor to AutoInc. She can be reached at

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