I don't think I'd worry about using an aftermarket part. Some companies spend a lot of time reverse engineering oem parts to learn all the important and necessary characteristics, then make little improvements. Just one example: they could find a sensor has a coil of very fine copper wire with the ends pulled tight to the connecting terminals. Repeated heating and cooling of the wire might cause the ends to flex and eventually break off from the terminals. To improve reliability, they could simply add a little slack to the wire.
That's the type of thing the original manufacturer might modify too, but if you realize that these types of things are mass produced by machines, it can actually be quite involved making a change to the way a machine operates.
Most manufacturers make dealers return parts that are replaced under warranty because they want to determine why the part failed. A perfect example is MAP sensors from the late '80s. The part was designed and built by GM. They had a 100 percent failure rate, ... So they supplied them to Chrysler. They had to come up with something better. Once it was redesigned, both companies had very little trouble with them. If they had just continued to use the old design, the aftermarket companies would have developed an improved version because there would have been a huge market for their product.
The earliest crankshaft position sensors were nothing more than a coil of wire wrapped around a magnet. Doesn't take much to figure them out. MAP sensors have a lot of miniaturized electronics that are impossible to figure out. The aftermarket guys might be able to design a similar part, but they could be unaware of one important detail that might show up under very rare operating conditions. For this reason, they might simply buy the part from the original manufaturer and rebox it with their own company name and part number. This can also be less expensive than trying to reinvent a complicated part. NAPA is the only company that sells an electric fuel pump for Chrysler vehicles that is as quiet as the original, because it comes from the same company. Caravan turn signal switches have three part numbers stamped on them. One is Chrysler's, one is Toyota's, and one is someone else's.
The point is, the aftermarket part could be better than the original, or the original could have design improvements. You also have to consider that suppliers are always being squeezed by the manufacturers to reduce the cost of the part. In the early '80s, Ford stopped using grease fittings in their ball joints. It cut their life expectancy to barely enough to get them out of the warranty period, but it saved them a nickel per fitting. Save four nickels per car and build a million cars, you save a million nickels, That continued to the early Escorts and Tempos that became known as "killer cars" due to their steering links falling apart. The aftermarket suppliers were quick to come up with a greatly improved part, but that better part never showed up at the dealership. The oem part lasted around 15,000 miles. The aftermarkeet, less expensive replacement had the normal life expectancy of well over 100,000 miles.
I would have no problem using a less expensive aftermarket part, but I think I would stick with the guys who specialize in car parts and earn their reputation on their reliability. Auto parts are not the specialty of hardware stores, so they might be willing to accept a higher failure rate. Sure, they will still have a warranty, but do you care about the warranty when you're sitting on the side of a country road on a Saturday night, after midnight?
Monday, March 1st, 2010 AT 4:29 AM