Mike, et al,
This is an issue that has been receiving a good bit of face time as of late. The terms OE, OEM, and aftermarket are often misunderstood and used incorrectly. It is my aim to shed clarity on this matter.
To begin let's define the terms:
OE: literally means Original Equipment. This is the same thing as a dealer (or MBC) supplied genuine part. An OE MB part will have a Star on it.
OEM: translates literally to Original Equipment Manufacturer. In a nutshell, these are parts produced by the same manufacturer of OE parts, but it does not guarantee that the OEM part is the same quality or even the same part as an OE part. I will expound on this later in the post.
Aftermarket: A third party producer of parts that is independent of the vehicle manufacturer. Bilstein is a prime example of a common aftermarket manufacturer.
So, are all OEM parts the same as OE? Is that Bosch remanufactured starter from India the same as the remanufactured Bosch unit sold to you in a MB box from the Classic Center? What about OEM Bosch spark plug wires vs. MB genuine? For that matter a Phoenix branded motor mount should be identical to the same sold through the dealer, no?
Fact is, no! They are, more often than not, different. 20 years ago the differences were often negligible, if any. Reality is today that the OEM part is often (not always) of lesser quality than the OE part. There are exceptions, and Mike picked one of them with referencing Mahle pistons (This is assuming we are referencing German made Mahle pistons as opposed to their Brazilian made cousins). While these exceptions do exist, it is important to not assume that the exception is the rule.
Let's explore an example more closely. Motor mounts. The OEM under scrutiny here will be Phoenix. An OE mount, will have a Star on it, MB part number, and the relevant color dots. What about those OEM mounts? They, too, have the MB part number on them and sometimes the colored dots. However, notice that where the Star was it has been ground off? Is that only because the part is being sold as an OEM? Truth of the matter is no; the part is physically different than what the MB dealer will sell you. What is different? The dimensions are the same and it looks identical excepting the ground off Star. These mounts with ground off Stars failed quality control for MB's standards. in general the rubber did not pass muster. However, they are good enough to still meet a lesser criteria and can hence be sold as an OEM. Bullocks you say? Having replaced an unfathomable amount of mounts over the years I can say without doubt that the genuine mount will almost always outlast the OEM mount by several orders of magnitude. Example: I have a client who is a most aggressive driver. OEM mounts are fortunate to last 6 months with him (it took a few sets to convince him to try the OE mounts). Once he switched to the genuine article, he has passed two years without any issue from his mounts. Driving style has not changed, if anything, he drives his car even harder than before. Proof enough for me, yet, I continue to see the consistent results on a regular basis thus reassuring this conclusion.
OK, so what about distributor caps, rotors, wires? Caps and rotors all seem to be consistently similar to the genuine article. I have not noted any significant difference. Wires are a different story. Tom Hanson can expound in detail the differences between an OEM set and OE; the differences are considerably more than just the box. For the older cars where MB does not sell wire sets, I purchase the individual components from MB and build my own wires. Since doing this I have yet to see a wire fail prematurely. Bremi, Beru, and Bosch OEMs; all I have had issues with in the past 10 or so years on multiple occasions. Things have changed in this arena, I see it on a daily basis.
Starters and alternators, too. "Bosch in the box" as I call them, have declined sharply in longevity. I bet a number of folks on this forum still have original alternators and/or starters in their car. Funny how the recent Bosch rebuilts seem to last 2-3 years in the daily drivers I come across. Buy the same article through MB and, voila, they are lasting considerably longer. Sad, still, is that a 35 year old starter and alternator will often outperform most of its contemporaries. When costs are cut, workmanship is one of the first items to suffer.
Same with diesel fuel injectors. When Bosch rebuilt their injectors in Germany, they were often well within spec and with narrow tolerances. Now, it is the luck of the draw with the India rebuilds. Get an injector from MB they are back at the proper spec. For a matched set (personally, I like them to be within a couple of bar from one another), you would need to re-calibrate them on your own or test many units.
When I examine the cost difference and the time involved, I find that in most instances it is cost effective to use the genuine article over an OEM. Fact is, I would make considerably more profit pushing OEM parts in my shop. Looking at things in the long-term, I know that OEM will generally not last as long nor perform as well as the OE part. Making the best overall product is what this is all about, at least for me. Remember the adage: "penny wise and pound foolish". It is all a numbers dance; what combination will provide the most effective use over time in relation to cost and physical effort. Blind faith in OEMs will frustrate most serious car owners in the long run.
A quick note about aftermarket. Is all aftermarket bad? For those of you that run Bilstein shocks, you know the answer is no. However, most aftermarket is produced with the least expensive processes and a weak attitude towards quality control. All bets are off when dealing in the aftermarket arena. Some are great, others horrible. Choose carefully.
Does MB make defects, sure they do! It happens to everyone. However in the end, it is my experience that the genuine article almost always stands the best chance of lasting longest and of being the best quality out of the box. Secondary to that, if your MB genuine part should fail (assuming proper installation, of course) see what MB will do to reconcile that problem. Will the OEM supplier stand by his parts in the same way? I sincerely doubt it.
In summation, to each his own. Each person has his or her individual list of priorities and expectations. As a degreed engineer, I want things as they are meant to be with the product performing as designed. At this point, it is my personal and professional experience that the majority of OEMs can no longer be trusted implicitly and need to be thoroughly scrutinized before being installed. OE, OEM, and aftermarket parts all have their place. Not all OEMs are bad, and many can still be trusted, but to say that all OEMs are as good or the same as OE is a fallacy.
