BMW argues the diesel engine remains the efficiency king on the highway, which is why the B57 still has a long life ahead. BMW estimates the new X5 with a six-cylinder diesel can cover 1,200 kilometers (745 miles) on the highway before refueling. The diesel engine is suffering a spectacular downfall in Europe. Australians have historically favored diesels as well, especially in larger vehicles driven outside cities, where the diesel engine remains the undisputed efficiency king. Diesel Lives On In The X5, X7, And Likely The X6The X5 just switched generations, going from G05 to G65.