The motor in particular has proven to be pretty reliable. Perhaps if we knew what car you were looking at as a whole we could better assist. Some common things to look out for on an M54 include vanos failures due to failing buna o rings, this is easy to fix in the M54 vs the older M52's. The ignition coils can fail as mileage increases, and can cost triple digits for a new coil, there are 6 of them due to being COP designs. Probably the worst problem has nothing to do with the motor at all, but the plastic expansion tank, which is liable to blow around 60k or more. preemptive replacement is the best course of action, in fact, it wouldnt hurt to do a number on the entire cooling system at that point. the radiator is usually good for 100k miles though, if you want to keep that for a bit longer. be warned, there is only about 2 gallons of coolant in most M54 setups, thats why they warm up so quick. but that also means that if you lose coolant pressure, that block will heat up lickity split. The M54 was probably mainly put in the E46 (aside from the x5, z3, E39, etc), so good places to look for more info include: http://www.bimmerfest.com/wiki/index.php?title=BMW_E46 http://www.e46fanatics.com/faq/faqs.php Cheers!
