So first, I read that the M3 doesn't have the same set up as non-Ms but I'm not so sure about that. I know there's a hose crossing over to the ET that we don't have, but I think that's just the way it makes the same connection we have to the ET from the upper hose. Just a hose instead of it being incorporated into upper hose fitting.
My car's second ET lasted 9 years. 9 years...and probably a good 200K miles. The first ET was replaced after 2 years.
I do think ET's fail because of overfilling...and made a thread about that...forget the title...maybe 'plastic or human error'?
My window regulator on driver's door was original up until a year or two ago. They're not crappy parts...they're just susceptible to owners who are misinformed, ignorant, dirty, or busy! I think regulators probably fail more because of owners opening windows when they're frozen...or maybe had been closed a long time in the heat and got stuck. Combine that with lack of a preventive and sensual coating of gummi pflege...what do you expect?
Most cars don't have an ET like we do. Jaguar does I know...not sure who else, but not everyone at all.
Our expansion tank is a thermal expansion tank...like in your home's thermal expansion tank. In conventional systems, the extra fluid leaves to overflow tank and returns...as explained. In ours, the air in ET (maybe 2 cups of it) is what buffers, cushions, the system. Air compresses much easier than water, you know, but when coolant heats, it expands and needs a place to go. Don't give it the air, it will take out an ET.
Also, have to say it doesn't bother me having a system that will blow apart before the engine does. If it was as rock solid as it seems some of you want, you'd then be moving extra pressure to where? The head gasket. No thanks, I'd prefer just replacing ET please.
Don't go hating on BMW guys. Continue on like this and your penance will be severe!