Hand calculation vs mfd mpg - way off

something is not right

 

Wow, that's a pretty big difference (45%!)

I tracked this for 12-1/2 years on my 2005. No more effort, it was just an extra feature of my mileage spreadsheet. Depending on how carefully I filled the tank (say not so full the time before, then super-full to the point of running into the overflow container the next time [or vice-versa]), I found a single tank could vary by as much as 20%. Those tanks were super-rare though, and the error was usually that far in the opposite direction on the next tank, confirming it was probably a fill error on my part.

After 12-1/2 years the two sets of total gallons used were only 3% apart, so overall my MFD agreed with reality nicely (probably better than my short-term hand calculations).

So I would look at a timeframe longer than 1 tank, and never assume you will get any kind of accuracy in your manual calculation if you refill after only a few pips. Do 80-90% whole tanks. However, if that was a full tank, then I'd keep an eye on it. You may actually have a malfunction there. That's a pretty big difference!

 

How many times have you done this? Is it always this much off? I don't know about Gen2, but for Gen3 and now with PRIME (without EV), the displayed mpg is always 5-8% better than hand calculated mpg. This deviation is quite constant. You may want to check again using odometer reading, not tripmeter.

 

In North America, the Gen 2 had a bladder inside the metal tank to reduce emissions, it was fantastic at that.
However, it greatly complicated filling the tank, calculating mileage, and knowing when to refill the tank. so owners hated it.

If your tank never seems to fill I offer: open the gas cap as soon as you get to the pump, the more time to vent, the more gas you can add. Try to add gas in the heat of the day, the bladder is more flexible when warm. if it still won't add gas, try the nozzle upside down.

The only effective way to determine your Mileage is to average tanks.

After running out twice I offer this:
If your mother in law is in the car, get gas with 3 pips.
with your spouse in the car, 2 pips means you never hear about it later.
With friends who do not mind carrying at least 3 gallons of gas before you attempt to restart, one pip is fine.
If the pip ever blinks pull over NOW.

 

so, we're in a gen2 forum, but your info says 2010

 

gotcha. definitely a bladder issue

 

I think you'll find the more tanks you calculate the more it'll true up. Just two tanks would pretty much cancel out any pumping technique variations, three for sure would do it.