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Old 01-09-2013, 06:56 PM
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dunderhi dunderhi is offline
Next: '18 AMG GT Roadster
Location: MD
Join Date: Dec 2006
Posts: 6,866
Mein Auto: 15 M6 vert, 15 328dxt
Originally Posted by jjsC6 View Post
I see some folks who question the car's calculated mpg. I seriously doubt if it is off by much at all, and it's likely to be as accurate as using the calculator method. If you calculate by "hand" are you sure your filling up the tank to the same level every time? Have you checked to see if the odometer is accurate?
To ensure accuracy, I record every gallon of fuel and every mile driven for a year or better. I typically check my odometer's accuracy using highway mile markers for at least a ten mile stretch. So yeah, I think the hand calculations are fairly accurate.

Originally Posted by jjsC6 View Post
The reality is that with the current electronics and information supplied on-line they very accurately measure how much fuel is being electronically metered to the engine. I'm sure there could be some variance, but it's very unlikely they are off by more than 1-2%. While I don't use a calculator, I frequently run the numbers in my head, and I've always done it. They aren't off by much.
My 335d's computer varied up and down, tended to read just a bit pessimistic. The 550 read just a bit optimistic. Although I only have a few data points, my X5M's computer is displaying 0.5 to 0.8 mpgs optimistic.

2015 M6 Drophead Coupé
2015 328xd Estate
2013 X5M Sport Utility Vehicle
2013 650xi 2 Door Fastback Saloon
2011 Dinan 5 Saloon
2011 335d Saloon

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