Saving weight is indeed critical to meeting the EPA mileage requirements. And the use of plastics is one way to do that. Unfortunately as noted the monkeys are working overtime. I am sure a proper plastic formulation can be found that will suit this application.
I can't wait to see how that proposed plastic engine works out. I have seen it in the news before and they are getting closer but this certainly does not bode well for the introduction of a plastic engine.
I suppose if I were charged with overseeing the weight reduction program I would enumerate all of the components and order them by weight, with the heaviest at the top of the list. Starting at the top with the heaviest items should allow for the biggest bang for the buck in terms of weight reduction.
Another approach would be to lighten the metal parts and reduce the parts count through more effective component design. I bet the metal intake manifold could be sufficiently redesigned to reduce the weight significantly but it might still cost more than the plastic manifold.
The collection of requirements that must be met represent a difficult balancing act. Cost, weight, reliability, design life, maintainability, all of these things affect the design. In this case, it would seem the monkeys tipped the balance too far and messed up the reliability and design life goals. At least it seems it was an easy fix although rather inconvenient.
Intake manifolds made of polyamide were first developed by BASF in Ludwigshafen, Germany in 1972 (with partners) and have now largely replaced metals because of optimized air flow, design freedom and general reductions in weight and cost. There have been some issues because of poor designs, but the materials have been a big success and now new plastics are being explored in response to higher under-the-hood temperatures (esp. turbocharging), demands for improved function integration, noise reduction and lower weight.
Curiosity overwhelms me. . .if you could tap the manifold and repair the issue with a simple plimbing fitting, why could the manufacturer not do it? I suspect that injection molded plastic parts are cheaper than those which must be machined, but I still think in terms of what is best over what is cheapest. I get a lot of great repair tips like this one from the Ford Truck forum, and they help me keep the old Aerostar on the road, even with 250,000 miles. There's probably a similar forum for Mustangs.
Truly a bit of bad 'luck' but the car is over 10 years old - just another investment in an older car! On the positive side, you will have the exquisite fun of either replacing the manifold yourself or paying somone to do so. See - a learning experience!
If you do a web search on this, you will find out you are not alone in this problem and that there was a legal settlement back in 2005 on exactly this problem. The plastic manifold was used on the 4.6L engine from 1996 until it was replaced (with an aluminum manifold) in 2002.
I'm sure there was a lot of work done to validate the design but, hey, stuff happens and the real world can be somewhat unpredictable.
Were there any zinc or brass parts in contact with the nylon intake manifold? Nylon is well-known for its chemical resistance. However, there are a few chemicals which are incompatible with nylon. One of them is zinc chloride. Unfortunately, this forms as a corrosion product when zinc is exposed to chlorides (e.g. salt). Nylon will "crumble" if it is exposed to this corrosion product. Just a thought.
It is possible that your manifold was not a design flaw and was just an unfortunate bad part that was supplied to Ford. I would imagine that if it was nylon, it was probably glass filled for better rigidity. If you have a short shot at the end of fill for glass filled nylon, you lose the nylon and just have glass at the end of fill. Over time this short can weaken and crumble.
I'm still scratching my head ---when I throw a few tools into my pickup to do a roadside repair, I don't usually take taps and pipe fittings. That comes with the second or third trip home to get the left-handed monkey wrench, taps and the like!!
You're a good man to be able to take just the right items!!
Having spent many years associated with fleet vehicles, this type of problem with molded plastic/rubber parts is not all that uncommon no matter of brand. As to the comment on the vehicle being "ten years old", I have seen molded and other part failures at all ages, including before the vehicle even left the dealer's lot. Age should not be an issue with vehicles, apply the same cost per hour of use evaluation to vehicles as is done with industrial equipment and the industrial equipment manufacturer would never make a sale. Few consider a vehicle to have a lifespan exceeding 200,000 miles or roughly 4,000 hours which is less than six months for a piece of industrial machinery. If one wishes to make excuses for EPA mandates or whatever as to why vehicles are not manufactured to higher quality, use-efficiency standards, why is the same not equally applied in all industries? If such were really the case, why then are the auto manufactures not taking these issues directly to the consumers who are in control of who gets elected to political office? The problems with the automotive industry do not lie anywhere except with the industry itself.
The same had happened to me a few years back with a 1993 Oldsmobile Eighty-Eight with the 3.8L-V6... I was too far from home but able to get to work and call the tow-truck... The mechanic did the same prcedure and as far as I know, it is still that way today.
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