Every time I fill up the gas tank I calculate my gas mileage by calculator and pump readings.It very seldom agrees with the DIC calculations,but there's no pattern to the difference.Sometimes the DIC reading is off on the high side,sometimes it's on the low side.Two fill ups ago,it was pessimistic(30.24 m.p.g. actual vs the DIC reading of 29.6),the last fill up it was optimistic(27.5m.p.g. actual vs 28.6 m.p.g. DIC reading).Anyone else notice this with their cars?

 

I noticed the same thing with mine. The only difference is that mine is always "pessimistic" Last time it showed I had gotten 29.6 MPG on a full tank when I had really gotten 30.9 MPG

 

From day one. I found that by not resetting the MPG and just reset the A trip [I use the B trip for trips that I need miles to & from] that it stays closer, alway .5-1.0 over calculator !

 

Two big factors.

#1 it is only average in the DIC, it will vary with driving ETC. Even the number of green lighs vs red can make a differance.

# 2 you put a different amount of gas in to make your tank full. Some times the gas in your filler tube alone can give you 1 MPG more.

The only way to be exact on your gas is to drive on identical conditions with the identical amount of gas. Just take the high and low readings and you will have as close of a reading as you get.

 

Mine is always high. I've been tracking the mileage since February, with 14 fillups, the DIC is averaging 5.5 % high ~ 1.4 mpg high every time.

My actual mileage over 4,627 miles is 25.2 vs. the DIC reading of 26.6. (city mileage is 21.6 and highway is 31.9.)

 

well said hyper, the likelyhood of to tanks having the same exact conditions is extremely slim.

 

That small discrepancy is easily accounted for by not filling to the same mark each time. With a 50 litre fill, a one litre extra or less represents a 2% error. The first two numbers above are 2 % apart. (One litre or quart difference could arise from half a litre overfilling last time and just half a litre underfilling this time.)

Putting the two fill-ups together, they disagree by less than 1%.

Worn down tires, for example, car distort your calculated mpg consistently.

 

Just the fill neck on the tank on most vehicles holds 1/2 gallon or more. Also I have a station that has a hill and if I fill with the neck to the high side it will take more fuel as all the air is purged out. One Gal make a world of differance.

If you are one MPG off with the DIC you are doing good.

 

I do try to fill the car up to the same point each time,at the same station,at the same pump.I fill the car until I can see the gas in the filler neck.So if there's a variance in the amount it would be negligible(less than a couple of tablespoons).That still wouldn't explain the sometimes high,sometimes low guesses of the DIC.

 

After driving from Calgary to Vancouver (1045 km or 640 miles) I used 1 tank of gas. It cost $52. CAD to fill. After I arrived and refilled the tank, the DIC estimated that I would get 999 km from the next tank.