If your area allows it (temperature wise) 20w50 can help. I run it in the X and only get smoke if idling for 15 minutes or more. Never at stop lights.

My brother in law is planning on buying the X in October so I'll tell him it will need valve stem seals in the future, it's expensive, and no I won't do it for you. LOL. If he ends up not buying it, I'll fix it when the oil consumption gets ridiculous or the smoke starts appearing at stop lights.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)