Mine is typically 1.2 - 1.3 mpg optimistic. My lifetime average mpg is 18.16 (hand calculated) and the truck says 19.4. Every time I check it, that’s about how far off it is. One time, when I was 100% freeway driving, it was perfectly accurate. It could have been a fluke...or because I was just steady cruising for a tank. My speedometer is pretty accurate according to the roadside speed registers they put in residential areas on occasion (the ones with the speed limit sign and digital readout of your speed).

My last vehicle was very accurate.

Yes, my hand calculation is more accurate. I have over 20,000 miles of documented fillups...with gallons to the third place. In every single incident, except the one that they agreed, the truck has always been high by 1.2 - 1.3 mpg. If the truck occasionally or half the time gave a pessimistic reading...that would be different.

Trucks can’t lie or tell the truth. All they can do is provide data based upon the sensor package they carry. Being an instrumentation specialist for 27 years, what I’ll add is that Ford doesn’t have test instrumentation installed in these trucks. They all have a stated accuracy, probably based on a BFSL graph standard. We can’t afford a truck that can accurately measure how much fuel is injected on each stroke in each cylinder. The instrumentation capable of those exacting measurements in each millisecond costs more than your truck (yeah, even if it’s a Raptor). What we have is low accuracy OEM transmitters and transducers that approximate the amount of fuel used, probably based on pressure, injection pulse width, and known average flow rates of the injectors. These things probably aren’t even temperature compensated. Why? Because it’s really not that important for our readout to be +/- 0.1% accurate. Accurate vs inaccurate read outs, when all these different accuracies are compounded, is surely biased towards being optimistic because they use their lab data to program the rate of fuel usage....and things always work better in a lab.

Think of the truck being as accurate as it needs it needs to be. However, when tolerances stack, you’ll have some that are very accurate, some that are not very accurate, and a bunch inbetween.

I’ll even play devils advocate and accept there must be some evaporation from the tank. Also, much like the truck, the gas pumps have flow meters. I’ve read that they are mandated to be better than .03%. That will literally be more than 100X more accurate than the sensor package on the truck. There is no mandate for your mpg readout to be accurate. Heck, your speedometer is only legally required to be +/- 10%.

You seem to think the truck sensors are much more accurate than they really are. This is my world, I know they are not high accuracy instruments. These instruments send electrical signals that are then interpreted by another device that has a stated accuracy. None of these are lab quality. I’m not guessing or taking someone else’s word for this....I know this as fact. Frankly, all these components are supplied by the lowest bidder. When thinking how ‘exact’ these things are...try googling flow matched fuel injectors....then you can start wondering why these would be needed on race engines if basic fuel injectors already know ‘exactly’ how much fuel they flow. If you want to believe it’s super accurate, feel free....it doesn’t effect me. I will say it’s as accurate as it needs to be and remain affordable, producible, and marketable.

If the Texaco fuel pumps were out of tolerance, that’s on them. I use my truck for work and travel extensively, so I’m frequently using different fuel brands and stations.

This is too off topic at this point for me. You don’t appear to want to learn about the systems, and by your response i can see you didn’t even try to research before replying. You are giving anecdotal evidence when referring to systems that are rated in scientific terms. The 2 don’t go together.