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Old 10-05-2012, 12:38 AM   #35
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Join Date: Jul 2011
Location: Charlotte NC
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My Ride: 2001 BMW 330ci
Originally Posted by EmFiftyFour View Post
My theory has been that the reason why they use plastic is because 1) its cheaper to make I bet and 2) they need parts on these cars to only survive the warrenty period. what happens when the warrenty is over for the second or third owner? they pay right out of pocket. i believe thats why some things on these cars have been designed the way they are
Find me a car out there that does not use plastics in 90% of their cooling system. I have posted extensively about why plastics are NOT a cheaper solution for car makers, and why they like to use them anyway, but I will just give you the broad view:
- The capital costs for plastic molds are HUGE. The one for the thermostat housing would easily be a $750k mold. And you can't just have one. They probably have a dozen. And when they stop making e46 thermostat housings, that mold is just scrap steel, because the only thing it can do is make e46 thermostat housings. Not to mention, the molds wear out. There is a limited number of parts that can be made before it is too worn to produce the dimensionally correct part. Plastic is abrasive to the mold. That single part has probably cost BMW millions of dollars in molds alone.

So, why use them?
- The parts come out of the mold ready to use, for the most part. No machining, no plating, painting, anodizing or other finish required. The same part made from aluminum is labor intensive. It requires casting, then machining operations, then finishing operations. Each of these steps introduces the chance for human error, scrapped parts loss, and dimensional variances, not to mention transportation from one facility to another. But, a part made in a properly operated plastic mold will have almost zero scrap loss, and will come out of the mold complete, and dimensionally correct, each one the same as the other. There is almost no dimensional variance.

Now, you are correct in stating that they will not last like metal parts, but they will outlive the warranty period. And yes, that is all they care about. But this has added a new type of preventative maintenance to cars, because you now have to replace parts based on age, and not because of a failure. It is now just a fact of life that this is the way things will be from now on. It sucks, but it will not stop. In fact, it will expand to other parts as time goes by.
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