[Bush Pilot]

I've seen that the plastic coolant flange that interfaces with the front of the motor is a common failure point and that an aluminum one is available as a retro-fit. Any idea why BMW would use plastic in this application? I'm not going to believe that it was to save money. I'm concerned that there is a reason they used plastic and with an aluminum one installed another issue could surface. For example plastic has a different coeffficient of thermal expansion than aluminum.

[ppointer]

I believe they wanted to use as much recyclable plastic as possible.

[Bush Pilot]

Are you joking? Plastic is lighter than Al. But Al is recyclable too.

[Luper52]

Well seeing as it's such a high failure rate on this piece, I would probably still lean towards "because it being cheaper to mass produce". I doubt they did it for any thermal properties because the plastic obviously can't withstand operating at that high of a temperature for a prolonged period of time.

Plus it's not nearly as drastic of a change as relocating the expansion tank to the other side and using an aluminum tank instead. Lots of guys do that as well when going single turbo. I wouldn't sweat it on a coolant flange. Plenty of other people run the aluminum flange on way higher horsepower builds. If engines built for 3x the factory power use it then it's good enough for me.

I don't know much about thermal dynamics but I'd have to guess in application the differences are negligible.

[Efthreeoh]

Originally Posted by Bush Pilot

I've seen that the plastic coolant flange that interfaces with the front of the motor is a common failure point and that an aluminum one is available as a retro-fit. Any idea why BMW would use plastic in this application? I'm not going to believe that it was to save money. I'm concerned that there is a reason they used plastic and with an aluminum one installed another issue could surface. For example plastic has a different coeffficient of thermal expansion than aluminum.

It was to save money. Manufacturing a plastic part in that specific configuration is vastly less expensive than casting an aluminum part then machining it to the required tolerances, or more expensively, machining the part from billit. While it seemingly is a high-failure rate part, it really only seems so because the failures are coming 10 to 15 years after the cars were built and have achieved high miles. I have a 25 year old Z3 M44 engine that has similar plastic cooling components (i.e.plastic hose bib connected to the cylinderhead) that I have never replaced. When I pulled the original hoses off my 2006 N52 E90 in 2012 at 240,000 miles, the bib was not in a deteriorated state. In fact in 2012 deteriorated bibs weren't yet even an issue. When I replaced the bib in my 2008 Z4 in 2020 at 100,000 miles, it was I little soft, but not close to failure.

I don't think N52/54 bib is the major quality issue that you are making it out to be. Plastics really don't have rates of thermal expansion like metals to, thermoplastics just melt. Heat cycling does over time change the structure of the plastic. But failure rates in the intervals this part sees, which is hundreds of thousands of miles and over a decade of use, is pretty good performance. My 1989 E30, which had an aluminum thermostat housing, failed from corrosion and left my wife on the side of the road after 8 years and 115,000 miles. I religiously followed the cooling system maintenance schedule and procedures only using BMW coolant and distilled water in that car. Stuff eventually just breaks.

My 2 cents on the subject.

[The Nightman]

Originally Posted by Bush Pilot

I'm not going to believe that it was to save money.

If manufacturers could build an entire car out of plastic that would still last the life of the warranty, they would!

But seeing how an o-ring seals the connection, I don't think thermal expansion is a consideration for this part.

[tcphoto]

Plastic is cheaper to manufacture and they only need to last as long as the warranty period. I'm thankful that mine lasted till I swapped it out at 130K miles, it did break into three pieces as I pulled it out but at least it didn't leave me stranded.

[StradaRedlands]

It was 100% specked to save a few pfennig.

Like. Every. Other. Part. On. Your. Car.

Parts are specked to be cheaper or to be installed quickly using less labor. Usually both.

Not a big deal to change out, and it lasts 100,000 miles, so can't really complain. I recommend changing the hose at the time, not just the flange.

[R3dLeader]

Not just cheaper but believe it or not they also do it for weight savings. That's why there's so much plastic in these engine bays, they're trying to save every pound possible for fuel economy reasons.