A couple months ago, I posted how this MB 229.51 spec oil had seemingly significantly increased the mpg on our '05 MB e320 cdi to the tune of 3-4mpg over the original 229.5 spec 0w40, but this was concluded over only the first few tanks of fuel. Now that I have calculated mileage over the last several thousand miles, I am more confident in posting the results. We previously got a consistent 32.9-34.1 mpg per tank (mixed city/highway) with the 0w40, and with identical driving habits, are now seeing well in excess of 35mpg with the 5w40 ESP (35.9 to be exact over the last 5k+ miles of mixed city/highway). We are even seeing in excess of 40mpg on occasion for highway driving, which had never been seen in the previous 100k+ miles. Anyone else tried this oil in a car that doesn't require it from the factory? It doesn't make sense than any 40wt oil could show such a significant mileage increase over a premium synthetic oil like M1 0w40, but this most definitely appears to be happening in our case.