this broke when changing expansion tank...
 

i believe it is number 4 in the realoem diagram. my question is....how does the thing come out? the plastic is rotten as hell. i tried to pull it out with needlenose pliers and it was like grabbing a paper towel. do i just break it to bits and dig the thing out?

http://c1552172.r72.cf0.rackcdn.com/225115_x600.jpg

http://www.realoem.com/bmw/diagrams/u/y/254.png

figured it out. it's the expansion tank thermostat a.k.a. Transmission cooler thermostat a.k.a. Oil Cooler Thermostat.

part number is 17111437362 and to get it out, you will probably have to break it. i was ultimately able to get it out by jamming pliers down through the middle of it and grabbing the hell out of it and pulling HARD and fast.

I try my best to avoid forcing the removal / installation of anything (unless it's designed to require force ) as typically doing so ends up causing problems. I suspect there's a way this part is designed to be removed without resorting to the method you used.

i could not agree more, which is why i was perplexed after gently lifting out the expansion tank and finding the top part of this piece already broken. in my initial thread, you saw where i said the plastic was pretty much rotten. VERY soft. obviously not how said plastic was designed initially, making the 'intended' method of removal somewhat less realistic.

Same thing happened to me when i changed the expansion tank. In the process of removing it, i ended up breaking part 12 which was not cool. So had to get another one.

yep. i actually chipped about a 2mm bit from the edge of the large hole on #12. i am going to try it and see if i can get away without replacing.

:-) you want to see if you can get away without replacing it " Transmission cooler thermostat". You sure you want to take that chance?
I had mine broke in my 04 E60. You want to change it. It broke because of the heat over time.

habla franglais?

i ordered a new transmission cooler thermostat which is #4 in the diagram. the plastic was soft and rotten.

i did not order a new radiator mounting piece #12 in the diagram. that's the piece which had the plastic nicked from it. the plastic on #12 was not soft and rotten. it chipped because i got a little bit handsy with a screwdriver trying to take out the thermostat.

While your in there should check any other plastic that Maybe in the same state.

everything seemed fine. the existing (original May 2003) expansion tank looked good as gold (with 132k miles). i just wanted to preempt any massive coolant incident. because i hate working with anti-freeze. period. i'll bang my knuckles for an hour rather than have to clean up anti-freeze for 10 minutes. not sure why. i just hate the way it feels.