MPG gauge is it accurate?

I was driving to the beach today, my first time on the highway, and I noted that I was originally averaging 33 MPG. Of course as I accelerated it went down and eventually averages what is in the picture. What I want to know is is our computer system accurate? I know I could do the fill up test but I rarely fill my car all the way up. If it is accurate then I am really impressed with the highway mileage.

I think it's roughly accurate, but you're definitely a lot gentler on yours than I am. I'm at 18.4mpg over 15k miles.

Cool. I believe the 30MPG but I was getting 33 until I down shifted a few times. Seemed kind of high but I guess it is possible. In the city I average 17-18 MPG like you do.

What speeds are you running at? I went on a three hour trip with an average speed of 65 I'd guess, was at about 27 MPG iirc.

I read somewhere on here that you can adjust the way it calculates if you ever find it to be inaccurate based on a proper fill up calculation.

I routinely get mileage like that on the open highway. The V6 is very economical if you can keep you foot out of it.

Most of us agree that if you do a hand calc, the computer shows about 2-3 mpg high or so. If you track it for a few fill ups, you can go into engineering test mode and change the multiplication factor the computer uses and get it extremely close.

N123456 said:

Most of us agree that if you do a hand calc, the computer shows about 2-3 mpg high or so. If you track it for a few fill ups, you can go into engineering test mode and change the multiplication factor the computer uses and get it extremely close.

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That's about right for mine. Hand calculation is usually right at 25 mpg for mostly highway driving. Computer will show 26-27.

Ok then it is a couple of ticks to high. I am going to do a hand calculation next time because it really intrigued me. I am a.....spirited driver so usually I don't see the best MPGs. I was averaging around 65 MPH because there were a lot of small towns that I know were just waiting. I think I want to do a Austin or Dallas trip soon and that should give me chance to see.

It's accurate. Verified by data from dSapce.

Fuel economy is heavily affected by the route's road grade, wind, gasoline quality, air temperature, tire pressure, load, and of course how you drive it.
FE reading from a solitary trip is not comparable to EPA UDDS cycle evaluation results at all though.

My Raptor is typically 2mpg below the computer.
Mustang typically 1-1.5 mpg below computer.

I track my fuel economy religiously using Fuelio.

Whenever I do a manual calculation it is consistently around 1.5 mpg lower than the cars computer. I'm not certain how much of that difference is due to error in the computer or error in the gas pumps.

Now, before you dismiss that as just crazy talk, keep in mind that all gas pumps are calibrated for accuracy within a specified window of "acceptable variation" by law. What that means is when the gov inspector comes by and tests the pumps at a particular station by pumping out a few gallons and measuring how much really comes out vs how much the pump says it pumped, it is perfectly legal for that pump to be off by a small percentage. So when the station owner is calibrating his pumps, where do you think that calibration is most likely to be at? Dead on accurate, or just a little bit off to the benefit of the station but still within legal tolerances?

I tracked mine over several tanks and a thousand miles to offset any single inaccurate tank fillup. As I recall my true mpg was about 2 mpg below indicated which matched my experience with a Ford Explorer I owned that also read optimistic by a couple mpg (every time I read a post about how great someone's gas mileage is I mentally deduct a couple mpg from their claim, unless they make clear they've adjusted theirs through engineering test mode or manually confirmed it the old fashioned way over at least a couple tanks of fillups).

I subsequently used the engineering test mode to adjust mine and it reads dead on now, last tested it over 2,000 miles of logged fillups and the gauge reads exactly what I measured over 2,000 miles. My lifetime avg mpg is 25.0 over 33k miles mixed driving.