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If a vehicle has an in-dash fuel mileage indicator, manually verifying the readings can be a surprise. Accurately calculating fuel mileage is very easy and can be revealing.

Corporate average fuel economy or CAFÉ standards, impose fines on manufacturers for vehicles below a given fuel mileage. Vehicle makers do their best to increase fuel mileage. Bureaucrats also wish to appear to be effective.

Punitive environments tend to foster fake figures

The environmental protection agency or EPA rates all new vehicles for fuel mileage. Most people realize, the rating is "blue sky" at best and many do not achieve what is promised.

Fuel mileage indicators are not always correct

Dash fuel mileage indicators seem to follow sometimes, the same trend. High mileage numbers make drivers feel better about their vehicle. Verifying the fuel mileage shown, may tell a slightly different story. Fuel mileage indicators are intended only as a guide. Most of the indicators I have checked show better fuel mileage than actually obtained.

Fuel mileage is a very simple calculation. Miles driven divided by gallons used equals miles per gallon. Being a gear head by nature, a few points immediately come to my mind.

Does my odometer read accurately and how do I accurately measure gallons used

Mile markers can be used to verify odometer accuracy

Verifying an odometer is also simple and should be done before calculating fuel mileage. Find a road with mile-markers and set your speed to exactly 60 MPH. Count the mile-markers while keeping track of time. One marker should pass for each minute driven. If five mile-markers are passed in five minutes the speedometer and odometer work properly.

Tracking gallons of fuel used also requires a method to be accurate. As a fuel tank nears full, the service station pump automatically cuts off. Once the pump stops, you can again add fuel and it will again cut off. The amount dispensed is always accurate, but the cut off point varies.  Continuing to add fuel, after the pump cuts off, can damage the evaporative emissions system.

Every pump and every fuel tank may cut off at slightly different gallons when filling

Fuel nozzles cut off at different levels and make fuel used harder to measure 

The fuel pump at one station may cut off at 15 gallons and another station may not cut off until 16 or more. Obviously this distorts any calculations. Using the same station and same pump may help, but this is not always practicable.

The more miles and the more tanks of fuel considered, the more accurate the reading. Many folks check every tank full and are sometimes perplexed at the variation. A better plan is calculating fuel mileage with several tanks of fuel. This will give a far more accurate reading than checking individual fill ups. Jotting the vehicle mileage on the fuel receipt makes this easy.

 fill up












miles per


 25,387 - 24,952 = 435 / 15.6 = 27.9
 25,838 - 25,387 = 451 / 17.2 = 26.2
 26,263 - 25,838 = 425 / 14.9 = 28.5
 26,758 - 26,263 = 495 / 18.1 = 27.4
 totals   1,806  / 65.8 = 27.5

 For tips on increasing fuel mileage, see our Detailed Topic on Driving for Better Fuel Mileage and Tips for Better Fuel Mileage


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