100 mpg--an artificial limit?

It's just a display limit. The calculation isn't limited.

 

Yup, consider the display zoomed up. If the display were to show up to 1000 mpg, Then you would see a line at the bottom of the screen all the time and occasional spikes up to 1000. It wouldn't be very useful. Toyota zoomed up the image to center around 50 mpg which is the average fuel economy of the Prius and is a nice round number.

 

The MPG on my ScanGauge shows around 1600MPG during glides with the engine off. My GenII could get up to 3000MPG....go figure.

 

With engine burning fuel, my ScanGauge would occasionally display numbers in the 100-300 mpg range, well above the dashboard limit of 100 mpg. This seems to correspond to a minimum burn rate of 0.2 GPH, which at 60 mph produces 300 mpg.

In my 2010, ScanGauge's GPH would often get stuck at 0.02 gallons per hour when the engine was actually off. I took this as a bug somewhere between the Prius ECU and ScanGauge. This means ScanGauge would show from 1000 mpg when gliding at 20 mph, to 3000 mpg when coasting at 60 mph. At other times it would display a correct 0.00 GPH and 9999 MPG.

I haven't been using those same displays since trading to an upgraded 2012, so cannot say if that bug is still present.

 

The torque app defaults at 255 mpgs with the engine off or if you are cruising downhill with the engine on you might hit it, also.

 

Certainly many cars will exceed 99.9 mpg, the limit on a 3 digit (xx.x) mpg display, as we have demonstrated on the long 11 mile descent into Bat Cave, NC from Hendersonville but you have to choose your highway carefully. For all but well selected paths, 99.9 mpg is good for 99.999% of driving. And yes a 4 digit (999.9) display will show mpg in excess of 100 mpg. Over 100 mpg perhaps more accurate but under 100 mpg probably no better.

 

ufourya calculated mpg to be 114 mpg at the pump, but he used two different pumps and was skeptical of that number, so he recommended his record be recorded at 99.9:

• fill-up calculation: Top 20 - MPG Record Holders | Page 31 | PriusChat
• "settling" for 99.9 mpg: Top 20 - MPG Record Holders | Page 32 | PriusChat
• This describes how to get the car's calculated mpg for mpg > 99.9: Top 20 - MPG Record Holders | Page 33 | PriusChat

 

I would actually prefer the display to show 000-999 mpg rather than 00.0-99.9 mpg. I could care less about tenths of a mpg. Whenever someone asks me what I get for mileage, I round it.

 

The display does show 3 digits on a PiP, 999 mpg. Time for an upgrade?

 

It's a scan gauge calibration issue. Otherwise there would be many threads about calculation errors being off by more than just 2-3 mpgs every fill-up.

 

Use Google Earth to make measurements between two distinct points you can identify while driving along a road.

 

I'm talking about the Prius C display. PiP cost too much for me unfortunately.

 

You can buy a Scan Gauge II for $159.00 From PC Shop or Amazon

 

You can use the Torque App with your Android phone with a $15-20 obd2 bluetooth adapter.

 

Slightly-related question: Does anyone know how to turn off the heartbeat in the Ultragauge display? I want about half-second gauge refreshes or quicker, but watching the heartbeat icon go that fast would probably drive me crazy, especially at a traffic light. Any way to turn it off? I figured I would ask before I buy a read-out gauge and Ultragauge looks nice.

 

Does the Ultragauge show the correct number of gallons used when you refuel? If not, it needs calibration.

These aftermarket gauges normally don't measure fuel consumption directly, but estimate it based on related information that is transmitted on the car's data bus. There are multiple points were this estimate can be knocked out of true, so calibration is likely necessary.