Mileage reporting overly optimistic

[BRGT350]

The best way I was told to think of EcoBoost was basically, you can have Eco or you can have Boost, but not Eco and Boost at the same time. The marketing message got it wrong. You can't drive with V6 performance and expect 4 cyclinder MPG, you can get 6 cylinder performance out of a 4 cylinder with the MPG being sacraficed.

As for the MPG display being wrong on purpose, I doubt that is the case. There is a tolerance on how accurate the speedometer and odometer is and also on how much fuel is in the tank. You stack up both tolerances and the computer reads different than what you calculated. There are too many possible errors in the calculations to be 100% the computer is reading false numbers. Just like DTE, it starts to go crazy under 12 miles to empty. You drive 100 yards slowly and the distance to empty drops by 2 miles. It isn't accurate, but that is the way it is. Besides, nobody seems to be able to calculate MPG accurately. The EPA test guidelines, magazines, manufactures, and owners have numbers all over the place. It really is a crappy system to measure fuel use.

 

[jmrtsus]

I have done two all interstate trips recently and one I averaged an indicated 36.9 and 36 mpg while cruise was set on 75 mph. The 36 mpg was calculated to be 35.5 mpg based on mileage indicated and fuel used. GPS says average speed was 73 mph so the speedometer reads 2mph high. This would also indicated the trip log mileage is also high. So using that number would also give incorrect mileage. That is fairly normal and matches my old Nissan Sentra. If the system measures gas flow by metered injections and uses mph to factor the mpg I would think that would feed into the inaccurate MPG readings displayed. I am very happy with 35 to 37 highway mpg and the performance of the ST.

 

[wythe4]

I'm finding that when my driving is consistent, my trip computer is within about 0.5 mpg of hand calculation. But, the trip computer seems to overestimate mpgs by like 2mpg when I drive conservatively on the interstate and then put my foot into it in town.