Change your oil anyway.. right after you bought it and new filter.

5w-30 Castrol Synthetic Edge ( Black bottle/Jug ).

Do not follow BMW interval of 10-15k mile oilchanges or whatever it is..

Change it every 5k at most 6k. I have a 4.8is also, and have the smoking problem... I suspect its cause PO followed dumb BMW intervals which contributes alot to this problem, and it was a Connecticut car.. so probably short trips in the cold winters, contributed even more with engine not to temp, and the ccv and all that.

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2006 X5 4.8is Fully Loaded