My MPG readout is completely inaccurate. Anywhere from 0.8 to 1.4mpg different from manually calculating it.

Is there anywhere for the owner OR dealership to adjust the computer readout so it is more accurate?

 

The manual method may not be so precise. The gas pump nozzle won't necessarily cut out at the same state of fill each and every time. Also, gasoline is sold by volume, not mass, so temperature plays a role, too.

It's probably safe to assume that the car's computer's reported MPG is not perfectly accurate, but it's probably precise. In other words, you can use it to observe trends in fuel consumption.

 

No. There's no way to adjust it by user or by dealer.

 

Also when you idling your computer it takes that into account but the manual calculation it does not.

 

^^^ This is a very good point!!

I belive the computer is MUCH more accurate than us. It knows to the millisecond how long the fuel injector is open and the speed of the vehicle. When we fill the tank, we really don't know at what level the tank is at never mind how accurate the gas pump is.

 

How do you know the MPG readout is completely inaccurate?

Did you ever compare the readout with actual math calculations by dividing the gallons consumed into the mileage traveled?

I did!



Starting from the left four tankfuls on a roadtrip from NJ to Florida
Two fillups from local driving in Florida, and four fill-ups on the return from Florida to New Jersey

A total of ten fill-ups starting from left to right.
I should mention that on the way down to Florida I did not use I95 which is the shortest route. Instead for the first time I started out going west on I78 to I81 in Harrisburg, PA then I81 south to I77 South to I26 picking up I95 in South Carolina. I wanted to stop by Fort Jackson SC where i had taken my basic training in the US Army over 50 years ago. They no longer allow visitors to military installations.
In any case this route is 100 miles longer than using I95.

Starting with a full tank from NJ
Fill-up #1 in Va I81 at a Pilot truck stop @$1.99 gal 340 miles traveled since the fill-up in NJ and took 15.824 gallons for a 24.49 MPG
Fill-up #2 at a Pilot truck stop in St Matthews,SC @$1.95 gal. 424 miles traveled and took 15.824 for 26.79 MPG
Fill-up #3 at a Pilot truck stop in St. Mary, Ga @$2.07 gal. Problem with the gas pump here as it shut off prematurely at 5.772 with 229 miles =39.67MPG. Tank was not full but vehicle computer read 24.9 MPG
Fill-up #4 at arrival in Florida at a Marathon @$2.24 gal. 326 miles and took 16.229 gallons for a 20.08 MPG which was also inaccurate. The computer read 26.5 MPG
Fill-up #5 local driving in Florida at a local Cumberland Farms @$2.24 gal. 228 miles and took 14.339 gallons for a 15.90 MPG
Fill-up #6 local driving short trips in Florida at the same Cumberland Farms station @$2.24 gallon. 228 miles and took 13.483 gallons for a 15.42 MPG and about to start the return to NJ
Fill-up #7 at a Pilot truck stop on I95 in St. Mary, Ga. @$2.19 gallon. 331 miles and took 13.643 gallons for a 24.26 MPG
Fill-up #8 at a I95 Loves Truck stop in Dillon,SC @$2.05 gallon. 304 miles and took 12.385 gallons for a 24.54 MPG
Fill-up #9 at a Loves Truck stop in Ruther Glen, VA. @$2.09 gallon. 298 miles and took 12.387.gallons for a 24.05 MPG
Fill-up #10 at my local WaWa station home in NJ @$2.39 gallon. 292 miles and took 11.254 gallons for a 25.94 MPG

Overall the entire round trip was 2540 miles and used a total of 101.377 gallons of regular 87 octane gasoline for a overall 25.05 MPG



Telcoman

 

Telcoman. That is exactly how I calculate it after every tank is mathematically and it is always off my 0.8-1.4mpg

 

That seems pretty accurate to me.

You and I are not dealing with precision scientific measuring equipment.

I should have mentioned my tire pressure was 35lbs on all four tires for my trip
MPG is also affected by humidity and outside temperature.

Telcoman