Parts are going to break. When they do, you just head to the parts dealer and pick up your replacement, right? Not exactly. Chances are that you’ll have quite a few options to work with. And as much of a blessing as that is, it can be a curse for car owners who struggle to differentiate between them all.
Many professionals and fellow consumers will tell you that your best bet is to stick with “OEM” or “Original Equipment Manufacturer” parts. After all, they’re what the manufacturer originally used when building the vehicle. While there is some sound logic here, OEM isn’t always the answer.
Some aftermarket suppliers produce parts that are designed to the exact same specifications (if not better) than OEM parts—and, in many cases, they’re cheaper. However, that also doesn’t mean that you should always buy aftermarket. There are a lot of poorly made parts out there that hurt buyers who are none the wiser.
So, what should you do? Start with a little education. By learning the differences between these parts and their acronyms, you can more confidently pick the right ones for your vehicle without guessing, overspending, or compromising on quality.
Learn the Lingo
To better determine what parts you should buy for your car when things break, it helps to know the lingo. Here are some simple definitions to clear things up.
OEM
OEM stands for “Original Equipment Manufacturer.” If a part carries this label, it means it is functionally identical to the part that your vehicle came with from the factory. Intended as direct replacements, OEM parts meet the exact specifications of the automaker and often carry the same warranty as the car itself.
Aftermarket
Aftermarket parts are made by third parties, not the original manufacturer. They’re designed to fit like OEM parts but can vary in quality, materials, and performance. Some are direct replacements, while others are intended as upgrades, but none were used by the automaker during production.
OES
OES stands for “Original Equipment Supplier” or, in some cases, “Original Equipment Service.” You’ll usually see this term alongside OEM, for example: “OEM/OES part” or simply “OE.” This is because OES parts are made by the same suppliers who provide OEM parts, often to the same specifications. They may be used in the vehicle’s production or sold later as replacement parts, and sometimes come at a lower price because they don’t carry the automaker’s logo or packaging.
Why OEM Isn’t Always Better
The idea that you should always use OEM parts when making repairs has some validity to it. These parts are essentially blessed by the manufacturer, bringing the exact specifications of the original components you’re replacing—which adds serious peace of mind. Ultimately, OEM is a solid choice, but it’s not always the superior one.
First, OEM parts aren’t always available. Once a vehicle goes out of production, it’s neither practical nor profitable for the manufacturer to keep producing every part indefinitely. In those cases, OES or aftermarket options step in to fill the gap and, as we’ve explained, many offer the same fit and reliability as OEM parts.
Second, price can be a deal-breaker. That OEM logo on the box often adds a premium, even when the part itself is identical to its OES counterpart—or in some cases, less capable than a well-made aftermarket version.
Finally, sometimes the original part design simply isn’t that great. Many aftermarket manufacturers have entire R&D departments dedicated to enhancing original parts’ designs and installations, from using sturdier materials and better internal components to improving coatings and upgrading tolerances. As a result, the right aftermarket upgrade can deliver the same fit as the factory part, but with better performance and longer life.
What to Look for in Aftermarket Parts
Learning your way around aftermarket parts can be an intimidating task. Today’s vehicles are made up of thousands of parts and various systems, all of which are vastly nuanced. It's a lot to take on at once, even if you’re a capable mechanic.
The good news is that a few basic tips are all you need to determine if an aftermarket part is a quality piece worth buying, something to be avoided, or actually an OES item in disguise. As you shop around, keep the following in mind:
- Check the description: Language like “updated” or “improved” lets you know a part likely improves upon the original’s limitations.
- Compare materials and construction: Sometimes, aftermarket suppliers produce parts made of sturdier materials—like aluminum oil filter housings where the automaker uses plastic. The improvements can be obvious from the surface, but if not, are usually highlighted in the product description.
- Cross-reference your part numbers: Many times, OES parts manufacturers reuse a part number without the carmaker’s labeling.
- Read forums regarding the exact problem with your vehicle: Contributors may tell you what parts to use and explain why they’re better than OEM in plain English.
- Compare pricing to claims: If a price is substantially lower than the competitors’ and it still claims to be just as good, if not better, it should be treated like a red flag and warrants further research.
- Look for warranty and testing standards: Aftermarket parts with manufacturer certifications or multi-year warranties often reflect design and build confidence.
Aftermarket Parts vs. Aftermarket Upgrades
There’s an entire segment of parts we haven’t fully explored: aftermarket upgrades. These are parts that provide alterations or improvements aimed at enhancing functionality or performance in a specific way. For example, in the case of suspension components, aftermarket upgrades may raise or lower the vehicle’s ride height, or change the feel of the car as it drives down the road. Upgraded engine components may improve horsepower, torque, and throttle response.
If a part breaks, should you consider upgrading? Only if that’s your primary goal.
Aftermarket upgrades will enhance a vehicle in some aspect, but you shouldn’t venture into that territory blindly. While some upgrades work well on their own, others hinge on other upgrades being present for optimal performance. If you’re not careful, you can end up throwing a bunch of money at a project you never planned for.
What About NOS?
“NOS” is a term that owners of older vehicles will hear a lot. It's an acronym found in the used parts market that means “new old stock.” It signals an OEM part that’s been unused and kept in storage since production.
NOS parts generally cost a premium because they’re a direct match to the quality of the parts used for cars that are no longer being built. Many of today’s aftermarket parts, even the best of them, aren’t an exact match to things made 50+ years ago. NOS parts allow collectors to rebuild their vehicles to the exact specification of the original manufacturer.
Whether or not you should use NOS parts comes down to the goal of your vehicle build. If you’re not worried about retaining a high collector value or having everything correct down to the smallest detail, they likely aren’t worth the added expense, especially if quality aftermarket alternatives are produced today. However, if authenticity is important to you, then it might be worth the investment.
Replacement Parts: Rule of Thumb
There’s a lot to keep in mind when you shop for automotive parts. Truth be told, knowing exactly what parts to buy often comes down to experience and product knowledge. As you learn what each type of part brings to the table and what your own demands are in different instances, you’ll get a better feel for which option is best for the situation. That said, until you get to that point, keep these tips in mind:
- OEM is great if it’s available, which is usually the case for new vehicles.
- OES is the best option to save money on quality parts, so it’s worth cross-referencing OEM part numbers to find if the same component is sold directly under the supplier’s brand.
- Aftermarket is better if you’re seeking design improvements over stock.
- OEM is better for retaining collector’s value, NOS is best for classics.
Need Help Finding the Right Part?
The world of automotive parts can be a maze, but you don’t have to navigate it alone. Parts Via’s customer service team can help you sort through our massive inventory to track down exactly what you need. And with our fast, FREE ship-to-store option, you can have your parts sent straight to the professionals who can install them for you—saving you time, guesswork, and a few busted knuckles.