OEM parts vs. aftermarket parts. It's a complicated story, it seems

My OEM front headlamb bulbs lasted 4 years before I replaced it with various aftermarket (and much cheaper) bulbs that didn’t last more than 1 year each (brands like Wagner, Sylvania, GE, all bought from RockAuto.)

OEM windshield wipers are much better than any aftermarket that I have ever tried. There’s no price penalty at all since I get the inserts only.

As far as I can tell, when it comes to oil and oil filters, there’s no real advantage (and no cost penalty) to using OEM vs. Mobil 1, Pennzoil, etc.


-internal engine parts
-spark plugs
-oxygen sensors
-maf sensors
-all sensors
-any part at all that requires a lot of labor to reach and replace.

WHat about struts? Are KYB/Monroe’s as good as OEM’s?

So, please chime in. What do you know about this topic?

What about rotors and brake-pads? Are the aftermarket stuff good?

Brakes . . . I’ve had severe noise problems with aftermarket pads, even when cutting the rotor

Not suspension parts. I would buy a Moog part anyday over OEM.

The quality of aftermarket brake parts varies widely, and it can become complicated by choosing to change the type of pad you use.

There is no absolute answer to your question.
For tranny and coolant fluids I prefer the manufacturer fluids, just because the wrong fluids can cause expensive damage.

For spark plugs, I like to choose one of my vehicle manufacturer’s OEM suppliers. But even then, if I go to a parts store unarmed and ask for only NGK or Nippon-Denso plugs they’ll offer me a choice of copper-core, platinum, or iridium. I prefer iridium plugs for all applications for cars built within the past 15 years, even though many originally came with platinum. No manufacturer uses copper core anymore.

I use the brightest headlight bulbs available for my application. I believe they’re called “Daystar” or something like that. They’re expensive, but IMHO they truly do put out more light.

For body parts, including lighting modules, switches, etc., I’ll order the cheapest aftermarket replacements. I’ve only been disappointed once, by a really really cheezey headlight module.

For wheels, the choices are countless. Even for OEM replacement wheels, you can buy refurbished wheels, aftermarket duplicates, or OEM. I’ve never been disappointed by an aftermarket duplicate.

For glass, it’s PPG all the way.

For engine parts, exhaust parts, cooling system parts, and drivetrain parts I go mostly aftermarket. I’ve very rarely been disappointed. For wheel bearings, I prefer Timken if I can get them for the application. For shocks & struts, Monroe is good, as are many other aftermarket parts. For belts, I go with Gates… and even then there are different grades.

There are countless parts in a car, and countless options for each.

My preference is to insist on better-quality parts whenever replacing the part in question is a pain in the anatomy.

See, the cost of replacing my truck’s clutch isn’t just the $150 part: it’s $150 PLUS the effort involved in tearing everything apart to get to it! I insist on quality (though not necessarily OEM) here so i don’t have to redo anytime soon.

For brakes, my current strategy is to run the cheapest pads possible, to maximize rotor life at the expense of pad life. Organic-compound cheapies are softer than semi-metallic or ceramic, so they ought to wear the discs less (and the pads more).

Given that replacing the pads is easier than my rotors (requires a hub overhaul), I go for the softer pads. Don’t know if it’s a popular strategy, but it’s my strategy.

I also run copper plugs: slightly better conductivity, cheaper too. (Downside being they only last half as long.)

P.S. Auto manufacturers don’t “make” oil, lightbulbs, etc…they contract this out and put their brand on them. Talk about using brand-x oil vs. OEM…they could be the same stuff in different bottles! Purolator makes “Motorcraft” (Ford) oil filters…though to slightly different specs.

I rarely buy anything OEM and rarely have any problems with new parts.

One thing to realize about OEM parts is that the manufacturer never makes them anyway. They’ll provide specs, sure. But vertical integration is long dead for most things in the auto industry. So often times those “aftermarket” parts are made by the company that makes the OEM parts. Good luck trying to track down the specifics of who makes what under what labels. It’s practically a full time job.

All the components you listed aren’t made by the vehicle manufacturer. They’re vendor/supplier components

Internal engine parts. Rings, bearings, valve springs, etc, supplied by a vendor.

Spark plugs, supplied by a vendor.

Gaskets, supplied by a vendor.

All sensors, supplied by a vendor.

Suspension components, supplied by a vendor.

Brake components, supplied by a vendor.

Exhaust components, supplied by a vendor.

So the major brand names in auto replacement parts are usually the suppliers/vendors to the auto industry in north America.


I use Motorcraft filters just because, at $0.50 premium over Purolator brand, I like how it looks “right.” Plus I’m convinced it’s a pretty good filter…but basically aesthetics.

You can’t get PPG labeled windshield anymore

It got sold a few years, and the windshields are now labeled PGW

Moving on, I’ve generally had good luck with Felpro for gaskets, and gates for hoses and belts

There have been some exceptions, but they were rare. I’m I’m replacing a belt which was worn, but not noisey, I’ll often use gates. If I’m replacing a belt for a noise, I only install factory parts

What you really have to be careful about, is if the aftermarket gasket duplicates the original part.
Some water pump gaskets are metal, with a rubber sealing ring in the middle. And some of the aftermarket gaskets are simply made out of gasket paper

I also don’t trust aftermarket thermostats which don’t look anything like the factory part

Everybody seems to swear by those aftermarket ceramic brake pads. I’ve found them to be extremely harsh, sometimes even noisey. I’ve even found them to make grooves in rotors. They make less dust than semi-metallic, but they have serious drawbacks, in my opinion

Very true, Tester, but there is a lot of junk out there and it can be impossible to find out who the vehicle manufacturers gets their parts from. So in some cases where and error might be costly, it’s sometimes best to go to the dealer. That’s the only way to ensure getting parts from the OEM supplier. For this discussion, I include in my definition of “parts” tranny fluids and coolant.

For the overwhelming majority of parts, aftermarket parts are just as good, often better if one is armed with the proper information, and anywhere from 1/2 to 1/3 the price of dealer parts.

One modifier too is the vehicle itself. IMHO it’s foolish to cheap out on critical parts for a new car, and just as foolish to invest in OEM parts for an old beater.


speaking of spending money to maintain a beater . . .

Unfortunately, many people aren’t very realistic about their cars. Meaning, they don’t realize the car which they think is so great, is actually a near worthless, poorly maintained, rough running POS with bald tires and a tuckered out suspension . . .

Well said.

@the same mountainbike

“Very true, Tester, but there is a lot of junk out there and it can be impossible to find out who the vehicle manufacturers get their parts from. So in some cases where the error might be costly, it’s best to go to the dealer”.



Remember that we’re talking about obtaining parts, not having work done.

Remember too that many of us have developed preferences over the years, for example my preference for Timken bearings, and Gates belts, and ceramic brake pads, but the average person has no idea what they’re buying.

Your question is impossible to answer. All of those OEM parts you list (and countless others) are made by the same companies that provide them to the aftermarket suppliers.
If bulbs are repeatedly failing then there’s an issue with touching the bulbs with bare hands, poor electrical connections, voltage surges, condensation, or what have you.

You mention Sylvania bulbs. Well, Sylvania produces them for Ford and Lord only knows who else.
DuraLast gasket sets from AutoZone? Manufactured by Fel-Pro.
Precision brand bearings? Manufactured by a number of companies including NSK, SKF, etc.

The list is endless and about the only thing that is really OEM to the car as new is the sheet metal and engine block; and the latter is a maybe at best.
Even seats and trim is farmed out so cars are pretty much a beef stew of ingredients acquired from all over to begin with.

The average person is getting components that the vehicle manufacterer can get at the cheapest cost.


Tester, that’s absolutely not true.

The vehicle manufacturers go through extensive qualification and validation testing with supplier provided parts, subassemblies, and assemblies. The process includes not only environmental and reliability testing, but also validation of the entire manufacturing process and qualification of the suppliers’ in-house programs that ensure that future parts and assemblies will remain the same quality as the ones originally tested and qualified for the initial production product. Once parts and assemblies are fully vetted, and the suppliers processes fully vetted, the information becomes entered into the design documentation, procurement, and manufacturing databases with the supplier information. Depending on the part/assembly, it can be a Source-controlled item, a Spec-controlled item, or simply ordered to the vehicle designer’s design drawing or documentation, in which base only a prequalified supplier for the parts will be used.

In many cases, manufacturers will send quality engineers to witness testing of subassemblies, and in many more the supplier’s test data must be shipped with the parts and evaluated upon receipt before acceptance of the parts.

Vehicle manufacturers do NOT simply buy parts from whoever quotes the cheapest price. It’s far more complicated than that. Vehicle manufacturers’ controls are far more sophisticated than that. I’ve been through numerous design, qualification, and validation processes for the automotive industry. I’ve been there.

The average person, on the other hand, has to choose from a market open to every kind of seller, from good product to outright junk. The only reasonable assurance they have that they’ll get the equivalent part to the one the vehicle manufacturer used is to go to a dealer. While there are a few crooks out there that violate their franchise agreement with the vehicle manufacturer, the dealer’s supply chain is generally pretty well controlled. The parts can be bought with a high level of confidence that they’ll be the equivalent to the part originally used.

I stand by my original post. If it’s important, and the cost of an error is high, the average person is probably better off getting the parts from the dealer. If it’s an unimportant part, the risk is acceptable, or the vehicle is a rarely used old beater, go cheap.

I have a question mountainbike and ask this in a respectful way. Without hashing all of the details out here again, I ran into a snag with a set of Ford main bearings about a year ago. Essenetially the thrust surfaces to control the crank end play varied by as much as .004 of an inch and one bearing half was basically .0025 of an inch thicker than its mate on the other side. That presents a huge problem when trying to figure out what to do about oil clearances which have a maximum allowable .0026.
As an analogy, think of welding 2 semi-circles together; say half of a 15" wheel rim and half of a 16" rim while trying to get a tire bead to seal.

A lengthy phone call with the bearing manufacturer led to their pulling the engineering drawings and they tell me that .0025 is an acceptable and normal deviation with those drawings done to Ford specs.

How does one explain an issue like that? To this day I cannot, and apparently the engineering department at the bearing manufacturer can’t either.

You can often tell as the dealer too will use aftermarket parts that work and produce just as good results. I would go the other way in thoughts of superior OEM sometimes. There are a whole line line of parts for towing, off road use and even general purpose that are so superior to OEM even the dealer tout their usage. ( Bilstein shocks example) Often the OEM parts are cheaper to buy then some aftermarket replacements. I am thinking now of some really good sound equipped and special purpose parts and lubricants that are absolutley necessary for better performing like brake pads, wheels and even floor mats from specialized manufacturers like Huskey etc. In many of the parts you listed, I feel there are better quality options to be found everywhere.

I know that dealers shop for cheap alternatives too when they prep their used cars of the same make for sale. Chinese made tires and parts galor are found on trade ins made ready for sale. And, some of those may be superior or some may not. .How many new cars actually arrive new on a car lot with decent OEM tires ? They often take the Walmart approach and buy the cheapest built tires for cut rate prices just to squeeze a profit on a part they do not warranty ! Same brake pads too !

I had to replace steel springs that I broke off roading once. After the poor performance that original Toyota supplied leaf spring packs provided, I went to a local shop who custom made them for me for less money and with a reputation so good for using better steel, even a local dealer and their employees used them instead of the original OEM supplied springs. This was true for some other suspension components as well. So, the bottom line for me is, get to know the mechanics who routinely work on your car whether they be at dealers or experienced independents. You would be surprised at what they recomend for you instead of OEM. Not dissing all of their use by any means. Just saying you can’t always make general statements about their quality.