Plastic parts on engines are a bad idea all the way around. They just can't withstand the temperatures, chemicals, vibration, etc. Funny, I've never seen an aluminum intake manifold start crumbling away. OK, I'll admit to seeing aluminum thermostat housings corrode, but only on poorly-maintained cars with leaking radiator hoses. And a t-stat housing is certainly a lot less than $300.
In 2009 we were left stranded 75 miles from home by our 2004 Chevy Aveo when the PLASTIC thermostat housing broke clean off. Suddenly coolant was spraying out from under the hood. There was no quick roadside fix, and it had to be towed home. To add insult to injury, the thermostat and housing are one complete unit which is a dealer-only part. Of course, it took a week to arrive as well. Luckily it only cost around $25 - and we were really lucky, because the dealer told me that the part number was being changed, as well as the price - to $58.
The intake manifold is a $300 part. This is not much money to have to spend to repair a 10-year-old car. Stop whining! Keep in mind, also, that you could probably convince Ford to provide a free replacement manifold, because it is a known defect.
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.
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.
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!!
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.
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.
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.
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.
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