Fuel economy just dropped by 22% after oil change?!

[tomrauser]

Hello, I bought my M56X new in 2012 and have had very little issues with it other than the dealerships not knowing enough about the car but that’s another story for another time.

I have 75,000 klm's on it now and always put Mobile one 0/40 in her and change it out about every 4000 klms due to climate i live in here in Canada. my issue is this last oil change at the local infinity dealership took my 100% stable 12.2 l/100 (mixed driving) down to 15.5 ! for the first time ever! i have put about 100klms on it since and it’s still at 15.5 l/100 OMG this is worse than my AMG63 gave me!
I have never seen the computer show me worse than 12.2 l/100 since new and best Highway I have seen is 10.5 l/100

Has anybody seen this before? yes new air filters installed at this time and still drives and feels good. Deaership has no idea why it would have dropped

[Ilya]

I would calculate it the old fashioned way (gallons filled / miles driven since last fillup) just to confirm it's the computer reading correctly. Maybe your computer is tits up?

Also, welcome to the forum.

[mazz]

100% stable 12.2 l/100 (mixed driving) down to 15.5 ! for the first time ever! i have put about 100klms on it since and it’s still at 15.5 l/100

sorry i don't understand that math , please explain your method of measuring it is apparently different than what i am use to. I could learn something. Also i am not comfortable with conclusion drawn after 100 miles or 100 klm especially with the computer as the source .After a couple tanks of gas using the old fashion method then start worrying.

[armybrat]

Hello, I bought my M56X new in 2012 and have had very little issues with it other than the dealerships not knowing enough about the car but that’s another story for another time.

I have 75,000 klm's on it now and always put Mobile one 0/40 in her and change it out about every 4000 klms due to climate i live in here in Canada. my issue is this last oil change at the local infinity dealership took my 100% stable 12.2 l/100 (mixed driving) down to 15.5 ! for the first time ever! i have put about 100klms on it since and it’s still at 15.5 l/100 OMG this is worse than my AMG63 gave me!
I have never seen the computer show me worse than 12.2 l/100 since new and best Highway I have seen is 10.5 l/100

Has anybody seen this before? yes new air filters installed at this time and still drives and feels good. Deaership has no idea why it would have dropped

Using your figures and converting them over to our system of gauging fuel consumption (miles/gallon, or mpg) I come up with you getting around 19.29 mpg mixed driving before the oil change and 15.19 mpg after the oil change. Personally, every 4000 km oil change seems pretty frequent to me, even in Canada I would think 6000 km would be sufficient but I don't live there so if it works for you that's ok. I know this time of year when the temps drop your car will run in open loop longer due to warm up time when the temps are colder. Air/fuel and MAF sensors could affect fuel consumption as well. I can't see an oil change affecting it unless they used a different blend oil this time. I would monitor your fuel usage for the duration of your oil change, as 100 km is not really far enough to form an opinion. I can tell a difference in my mileage when the outside temps drop.