^^think of these new diesels as a refinement to the older diesels both American and foreign. The most or highest mpg I've gotten was 31-32mpg @ 80mph with cruise control on. Remember to get the true benefit of the diesel motor you gotta hit the open road. Both of my diesels never liked NYC style stop and go extended traffic. As far as any mechanical issues I only had to make a not routine stop at the dealer was when the urea level was getting low. That was with emissions though. I bought a 2012 x5d new and my 2015 x5d was also purchased new but ordered the way I wanted it. I'm not keen on flying due to family size so the x5d fits the bill perfectly.