Check differential mount bushing- lucky # 13 in this diagram
http://www.realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=33_0124&hg=33&fg=10 They tend to tear up.
Also, bad gauge cluster issues can cause a false indication of overheatring
-BUT_
overheating will crack the cylinder head. Check the #2 (from the front) spark plug to see if it is wet. If it is shiney, it probably is coolant and the head is cracked.
Motor mounts are liquid filled, and pretty expensive as well as a bitch to replace. if the car shakes alot (especially at startup), those mounts are probably shot.
A mysterious rattle from the rear windshield area is usually a broken rear shock mount- my cars need 'em, but I haven't gotten around to it. I think the parts are only $80.00 each, and the work not too complex- no welding anyway.
One very important maintenance item I forgot to mention is a timing chain tensioner- easy replacement in 5 minutes...
Thats all I got right now...
