Quote:
Originally Posted by infinitekidM2C
THe 135 does not age well
water pumps
oil leaks
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There are not yet any 15 year old M235i to compare, but the N55 in the M235i is a little simpler than the N54 in the 135i since it is single turbo rather than twin. The same water pump is used for both motors but maybe accessibility is better on the N55 in the M235i? I doubt there is much difference in gaskets and seals that fail over time and cause oil leaks. That may be more of an age factor, unless maybe the single turbo design reduces under hood heat significantly.
Generally, though, the N55 is viewed as being more reliable. I think a lot of N54 problems are due to deferred maintenance or neglect. In the hands of a DIYer who stays on top of maintenance, they are fine. If you need to pay a shop to maintain your 15 year old turbo BMW, you will be spending a lot.