ScanGauge E mileage calculation.

[JockoT]

While filling up today I noted all the "Tank" readings on the ScanGauge E and was surprised to see it had calculated the mileage driven 2.5% less than the vehicle odometer. As a result it had calculated poorer mpg value than actual.
There doesn't seem to be any calibration for the mileage.
Has anyone else experienced this and did you figure out a work-a-round?
Or, like me, did you just shrug and say, "it's all relative anyway".

[MetroMPG]

There is calibration available via a user-settable "offset" both for speed and for fuel used.

Did you get a manual with yours? If not, check:

https://www.scangauge.com/support/user-manuals/

[JockoT]

Originally Posted by MetroMPG

There is calibration available via a user-settable "offset" both for speed and for fuel used.

I have checked the speed against the GPS on my Sat Nav and Dash Cam and it is near as makes no difference, so no offset required.
I adjusted the fuel used at the second top up (via the user-settable "offset"), and it was very close at today's top up. I adjusted it slightly to make it spot on.
It is just the actual miles it thinks I have done that is light.

[MetroMPG]

Have you checked your GPS against the car's odometer? Seems that's where the difference may lie.

[JockoT]

You may have something there. I have never checked the odometer against the GPS. I don't really know how I could do that. I do know that the speedometer reads about 10% slow verses the Sat Nav. 30 mph on the speedometer is 27 mph on the Sat Nav (and roadside safety speed indicators). That would mean that if I drove at a speedometer reading of 30 mph for 10 hours I would have actually only done 270 miles where the odometer would say 300. That is even worse than the figures I actually measured which would equate to 29 mph at an indicated 30. Mind you, it doesn't seem to be a uniform 10% at all speeds so that may help explain it.
I'll keep logging my calculated mpg and treat the ScanGauge as an indication. After all, that is what I have done for the past 50 years! I'll just be aware of the difference.

[puddleglum]

Check your GPS for a distance reading, it probably has one somewhere. If not there are GPS phone apps that track distance. The odometers on both my cars are off from actual.

[JockoT]

Do you mean plan a route, drive it, and see how the odometer compares with the distance the Sat Nav had planned?

[vskid3]

Most cars have the speedometer show a slightly higher speed than actual, possibly to reduce the manufacturer's liability for speeding tickets. The odometer is usually much more accurate, though factors like different tires can change that. If you have your scangauge show speed, it'll probably be pretty close to what your GPS says. The car knows the actual speed and just has the speedometer show higher.

Does your GPS have any sort of trip odometer? If so, you can reset that and the car's trip odometer before going on a drive and compare the two at the end (preferably a long highway drive).

[JockoT]

Unfortunately the GPS doesn't have an odometer function. The ScanGauge obviously uses the same speed/distance sensor (mounted on the transmission) that the Speedometer/Odometer uses. The Dashboard Fuel Display was within 1% of the the calculated mpg which was much closer than the ScanGauge had figured on, which is probably down to the fact that the fuel had been used over a greater mileage than the ScanGauge thought.
I am beginning to think my best bet is just to use the ScanGauge to show how my fuel efficiency is going, mile by mile, then calculate the actual mpg at fill up, as I have done for the past 50 years.
Trip odometer reading / gallons to fill up = Miles per gallon.