A 100K 6cyl BMW is just fine. I make a point of avoiding the Turbo Charged models. Due to a nightmare of an N55 335 my husband had. The Straight 6 engine is doggy but gets the job done and is a snap to work on. If you buy one, make sure that is has been taken care of. That is whats key. They're good cars. As others have said, buy a scanning tool to see whats going on with the vehicle. If youre going with a non-lci 07-10, make sure its a 2010 as you will get the better navigation.

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2010 X5 3.0 X-drive Titanium Silver/Black
2018 Ford F-150 Platinum Crew
2010 528xi (His)
2017 M2 Manual (His)

Former Headaches:
2008 X5 RIP
2015 M235
2013 135is
2009 535xi Wagon (JUNK)
2007 530xi 6spd CPO Sport (Best Damn Car EVER)
2011 335xi M-sport Coupe 6spd (Sex on Wheels)
2010 550GT "CPO" (Junk)
2012 X5 35d "CPO" (More Junk)
2004 330i ZHP Sedan
2002 325xi Wagon
2000 323i Sedan
1998 M3 Sedan
1992 325i Sedan