I drive a 2014 is250 f sport with 75,000 miles. Yesterday i filled up after driving 436 miles on a tank of gas according to my trip A. I reset the trip a every fillup. The mpg counter says i got 26.9 so if you do the math i should have at least 16.2 gallons before filling up, but the pump stopped after 17.2 (16.8 then added a few clicks). So technically my mpg is 25.9 with a calculator. Is anyone elses mpg counter off by an mpg or so? Also noticed that the range only shows 409 after filling up instead of 436 miles from the previous trip A (theoretically speaking because thats how many miles it was capable of driving on a tank of gas) and dont mind the warning light, i just need an oil change soon

Before i filled up


After
i drove last time)

 

They're not exactly on the money so yes, they can vary a few mpgs typically.

 

Its closer than I would expect it to be in calculating mpg. Will never be exact.

And you filled up 17.2???? Thsts basically tank capacity, were you running out of gas?. Most I've filled up was 16 and that's pushing it.

I would advise against the few clicks after the pump clicks off when you're full. Actually causes harm.

 

^^ I was thinking the same thing, but also you have to take into consideration that the instrument cluster is simply calculating based off of ecu inputs which will put it into ballpark. Now the calculation is based on the tank itself, not the neck or filling tube. Also to touch on the extra clicks, avoid the ever tempting top off. This can and will cause damage to the evap systems on all the new Toyota/Lexus models in production today.

Mine is usually off by 2-4mpg every time I fill up. Worse when just city driving vs highway.

 

no it was actually 16.8 but i clicked it to 17.2. Also i find it weird that the fuel gauge will sit on full for about the first 50-60 miles then it drops. Makes it difficult to judge where the 3/4 mark would be at.....

 

I look at how much miles I have left on a tank, which is fairly accurate.

 

your "miles left" is also calculated partially by your driving patterns (the more aggressive, the less fuel it'll show)

 

how long was it saying your range was 0 miles before you filled up?

What I know is I have about 3 gallons in the tank when it tells me my range is 0 miles. But I follow the trip milage, reset every fillip, and when I hit 300 miles I know I ahould fill up by 330 or next time its convenient, soon. At that point I normally fill up a hair over 15 gallons. I'm getting about 22.5 mpg. IS350.

I think it's best to always leave at least 2 gallons in the tank. Or better yet, follow the range meter on the dash somewhat. 16.8 gal fillip means you may be damaging the fuel pump and certainly very close to running out of gas.
Just based on reading and other threads here.

Yeah every car I've had is like that on the 1st 1/4 tank. I think the meter may take a while before fuel level drops low enough to start reading fuel level. I used to think mpg was much better 1st half tank, but haven't tested enough to be sure.

 

it showed 403 when i filled up that time and i usually reset my Trip B when the gas light comes on. It showed that i went for 65.6 miles after the light and went 37.8 miles past 0 or when it says “refuel”

 

The fact the mpg was that close to your calculation is a miracle.
The way the vehicle calculates mpg will never be as accurate as you doing it yourself, it's more of a guideline.
It's like buying a car based on the EPA fuel rating and never being able to achieve them...it's more of a guideline to compare the fuel consumption against other vehicles that undergo the same unrealistic test.

I've also noticed that when the tank is full it takes a long time (distance) before it starts to drop.
Again, as much as the sending unit is calibrated to give an accurate reading of tank capacity, the tank is in the shape of a saddle. so it's going to be only so accurate.
This means the area with the most fuel volume is at the top part of the tank, and then at the bottom you're trying to measure the combined capacity of the two sides of the lower part of the saddle.
Every car I've owned has had some spot on the fuel gauge where the needle just doesn't seem to move for the longest time...realistically that's usually where the tank volume is the largest.

 

On board MPG calculator are always off, it does not take account the initial start or other factors like that, the only true way to measure is by acutal miles drive versus fuel used, even then it's not 100% because the speedo typically off also and reads higher, you might be really going 70 but the speedo shows 73, manufacture are optimistic on the speedo .

Only way to find the real numbers is GPS miles versus acutally fuel used.