Turbo Performance is absolutely right. In order to ACCURATELY HAND CALCULATE mileage, you must fill it with fuel to the filler neck. By not doing this, you have completely defeated the purpose of hand calculating your mileage.
deckocards90 said:
No, because that goes above the sensor or what ever is in the tank, I used to do it that way but found its inaccurate.
Sorry, but you've got it wrong. With this statement, you just proved that your display is inaccurate.
You have already mentioned that you run with a tuner on your truck in econo mode. Any time you modify a vehicle, diesel or gas, any sensors/scanners/gauges you try to use to calculate mileage can no longer be considered reliable. The reason is that modifications change how the PCM will calculate engine load vs throttle position. Since it's no longer stock (and the PCM requires stock calibrations to calculate mileage), then they can no longer be considered accurate. Even in stock form, the electronic mileage calculations are not always correct. They are simply a lazy man's guide, to give you a close estimate of mileage, but not an accurate representation.
Again, you mentioned that your display is accurate with your hand calculations. However, since you don't properly fill up all the way, you've force your hand calculations to be consistent with an electronic display. THIS IS THE WRONG WAY TO DO IT! If you fill with fuel all the way to the filler neck, run it empty, then hand calculate mileage, and it's different than your display... IT MEANS THE DISPLAY IS INACCURATE. As I already mentioned, you've already proved to us that your display is inaccurate, since you are getting different readings than what you hand calculate when you fill up to the filler neck.
Why must you fill up with fuel to the filler neck? Simple, the issue is foam. As you fill a diesel tank up, the fuel foams up. What happens is the foam reaches the filler neck, and automatically clicks off the pump. You might think the tank is full, but it isn't. Depending on the tank configuration and the amount of foam, you could still add anywhere between a 1/2 gallon to 8 gallons worth of fuel. Problem is, you don't know how much foam is in there at each fillup, so your calculations will never be based on the same amount of fuel in the tank. The ONLY way to be certain is to fill up with fuel, not foam, to the filler neck. That is how you guarantee that you are calculating fuel mileage from the exact same quantity of fuel.
Start over on your mileage calculations, and fill up with fuel to the filler neck. Otherwise, you don't have a leg to stand on when it comes to reporting your mileage results with hydrogen.