Was just curious. Over the last few tanks of gas I've been looking at the mileage vs. what the MPG meter says on my 16 350F. Based on the miles driven it didn't make sense so I stashed the gas receipts and wrote down the miles driven on them to experiment a bit.

Using the old fashioned way on 3 tanks of gas..which should be accurate(gas in, miles driven, a calculator)...I calculate 21.94 MPG. Thats about 85% city, normal mode, I'd say 50/50 windows open/closed, A/C on, Shell Vpower 93 from same station each fill up. MPG meter pretty consistent about 19.8.

Not griping about the gas mileage, I know what I bought and don't mind feeding it the good stuff. Just wondering if anybody else is seeing the same.

 

I noticed the same thing! The MPG meter is always a bit over what I calculated manually. I do the same thing to follow gas mileage : stack up gas bills. But I stopped doing so and just entered everything in an Excel sheet that calculates everything for me.

I reset the MPG meter each time I gas. The next time I gas, I write down on the gas bill the mileage and the MPG, then I reset the counter again. I go home and enter the numbers in my Excel sheet and the MPG I obtain is always a bit lower than the car's MPG... around 1MPG

Don't know why... but I don't really trust the car's MPG since the manual/old school way is the most precise thing! I only use it as an estimate, it gives you a good idea but not the real thing I believe.

PS: everytime I gas, it's a full tank! I know full tanks aren't always precise either... but it definitely won't be off my 1MPG?!

 

Not griping about the gas mileage, I know what I bought and don't mind feeding it the good stuff. Just wondering if anybody else is seeing the same.[/QUOTE]

I was wondering the same. Curious as to what you all are getting as your mileage "range" after a fill up. Have less than 2K, premium, 50/50 mixed hwy/city. Not a 350 but a 300 F-Sport AWD. My 2014 250 AWD range always read 330/340 range and the 300 is reading 280/290. Knew going in that the mileage would be less but didn't think it would be "THAT" much different.

 

It overcalculates to make the MPG look better. The difference is between 1-2 MPG

 

That's what I find odd though, I'm getting opposite those results. My calculation over 3 tanks of gas = just under 22 MPG. The car is saying just under 20.
I just gased up again today so tank number 4 and again I'm getting constant results. 21.85 MPG by my miles/gallons calculation. Car says 19.7. No real changes do my driving conditions or fuel (same Shell station/Vpower 93)

 

On board gauges are historically a bit off, It is useful
for the fuel gauge to be pessimistic so you do not
run out of gas and for the Speedometer to be a bit
optimistic to preclude a ticket. I have checked the
accuracy of a dozen cars over the years and found
the same conditions you all have, a bit hopeful but
not quite accurate.

 

I used to manually check in both my RX and my IS, but never found the meter to be off by more than .1 mpg, so I don't bother anymore.

 

Now that I'll agree with. I just find the MPG meter useful for glancing down to find that sweet spot on the throttle when cruising at a consistent speed to max out efficiency. Not that I'm a tree hugger trying to hyper mile or anything, would have bought a Prius in that case

 

I seldom looked at the MPG. I only use the instantaneous one while cruising on freeway. Otherwise, I just slam the gas and don't care the MPG at all. It's a 3.5L V6 NA engine afterall

 

After calculating it at the gas station, mine is off by 1 MPG. I get an average 25MPG (70 freeway with LA traffic/30 local)

 

Don't get me wrong...I'm all for that. I would have bought the boosted 4-banger if I cared. It's just something I pay attention to, I'm programmed for it due to the job. (Look at my screen name) I floor it as I please then go to the gas station when the light comes on in the car. In the jet, well....

 

I enjoy tracking my vehicles’ economy, even when driving gas guzzlers. It is just part of my personality. I primarily verify highway economy, so that I can make generalized comparisons between vehicles, in addition to monitoring the efficiency or lack thereof for a specific single vehicle. City driving is too varied to make vehicle to vehicle comparisons, so I stick to highway MPG only. For that matter, city driving variables can make it difficult to compare even when only testing a single vehicle, unless tested over an extended period of time.
My wife drives a 2015 IS350 Convertible RWD and I drive a 2015 GS350 F Sport RWD (additionally a 4x4 Suburban). The IS consistently over estimates its economy by about 1 MPG and the GS does the opposite by consistently under estimating its economy by about 1 MPG. My Suburban does both, with no consistency, by over and under estimating its MPG by as much as 1+ MPG, but most of the time it is within 0.5 MPG of accuracy.

Based on mathematical calculations of mileage and gallons consumed, at 80 MPH on the Texas interstate, the IS has averaged 24.7 MPG, the GS has averaged 27.2 MPG, and the Suburban has averaged 14.9 MPG. All 3 vehicles are typically fueled at the same gas station with the IS and GS getting Premium 93 octane and the Suburban getting Regular 87 octane.
I have never owned a vehicle that accurately calculated its economy. All of them have had their own particular characteristics and variations. From my 2nd vehicle that calculated its own economy up to the present 3 vehicles, I have learned that I have my preferences among characteristics. I prefer the characteristic of a system that consistently under estimates economy. It appears to me that the estimated Cruising Range always seems to “stretch” as it counts down from a full tank in vehicles that tend to under estimate their economy. That helps ensure I make it to my next planned fuel stop, if I am cutting it close. I sometimes do that so I can stop at familiar places vs stopping wherever I begin running low.
The worst estimated fuel economy calculation system I have ever seen was on my buddy’s Mercedes Benz E350. When you reset the system, it would start out showing an average of 23 MPG, instead of the truth of the situation, which is 0 MPG. Then when you pull away from the pump the car would begin lowering the average from 23 MPG, instead of increasing from 0 MPG, as is reality. Consequently, his car always significantly over estimated its economy.

 

In my opinion, I don't think anyone can calculated an accurate fuel economy. How you add the idling time in your calculation?

 

Idling still counts. During idle, you're getting 0 mpg (not moving, still using gas). So when you calculate your total miles driven divided by the total number of gallons used, the time spent idling will be included in that, as it is reflected in the gallons used.

The mpg computer factors it in as well, which is why you can start to see the average mpg number go down as you sit at a traffic light (using gas and getting 0 mpg, bringing your average mileage down).

 

That is why I stated above that I primarily calculate highway mileage. It is much easier to make accurate calculations, especially over multiple fill ups.