The fact that we have a few X5's with well over 200k miles is a good indicator. My X5 4.6is has 214k miles on it, and that's on the original engine. I did have to do a chain guide rebuild at 213k miles, but the fact that the engine made it to 213k miles without any major work is quite impressive. The original transmission made it to 200k before its rebuild as well. The i6-powered X5's last even longer.

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2003 X5 4.6 | 2000 540i Touring

Formerly owned:
2004 Range Rover | 2000 M5 | 2000 540i/6
1995 750il | 2003 Mercedes S500 | 2003 540i/6