How accurate is a Scangauge 2 for MPG?
 

My Scangauge 2 shows that my dark blue 2005 Civic gets reduced mileage when going up hills or accelerating, and increased mileage when going down hill or stopping. That makes sense. What does NOT make sense is that the MPG is highest at around 60-70 MPH. Should I just drive the speed that it reports the best mileage where legal and safe? A friend said that I should believe my Scangauge because my car will get its best mileage at higher speeds because, unlike his truck, my car is aerodynamic, so it is more efficient at a higher speed. That sort of makes sense. Is he right? Thanks, I want to save fuel by driving fast if possible:)

It's accurate once it's calibrated, but it's relatively accurate even before that- higher numbers, whether or not they're "real" are higher than lower numbers.

Gearing can leave the engine at its most efficient spot, and steady cruising doesn't put too much load on an engine, especially on something aerodynamic. My Fit does best between 40 an 50 mph because it's a brick.

Calibrate it at every fill up for a while, and the numbers will get more accurate and you'll be able to believe the screen a lot more.

Generally, on a level road your car will get its best mileage when it shifts into top gear.

(Is yours manual or automatic? Make a garage entry so your vehicle details are accessible under your username!)

The instantaneous readings are accurate once you've got it calibrated to your car.

Thanks a lot! It has a 4 speed automatic transmission. Also, how do I calibrate my Scangauge? I bought it used and it did not come with the manual.

When you fill, you go something like:

MORE > FILL UP

And it gives you the chance to enter or correct the volume of fuel you actually purchased in place of the volume of fuel the SG calculated you burned. You're adjusting a "fuel offset" which is applied to further calculations.

Note: You can also adjust a speed/odometer offset.

I'm sure you can still get the user manual from their site. Yup:

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

My experience, comparing it against the Insight's built-in gauge, is that it's not even close.

But which one is right?

That's mainly because the ScanGauge isn't designed for lean burn vehicles. It assumes 14.7 to 1 air/fuel ratio.

I wish I could get ethanol free fuel in Ohio. In North Carolina, I used to get ethanol free fuel from a Shell near work, but I can't find ethanol free fuel.

If looking for Ethanol free fuel in the states, try this site:

https://www.pure-gas.org/

The Insight's built-in gauge tracks actual mpg calculated from fillups & distance pretty closely, and miles by odometer is as accurate as I can measure. And what it displays seems reasonable, vs the SG's sometimes wildly unreasonable values. As (IIRC here) showing 100 mpg going up a hill where the Insight shows 50, then showing 50 down the other side where the Insight's display is pegged at 150, and the SG is showing it's in DFCO.

PS: I do have an SG that dates from about 2004 or so, soon after I got the car. Recent versions could do a better job. And my examples are from memory of the first year or so - I haven't used the mpg stuff since.

When you fill up do you tell the Insight how much fuel it took to fill the tank? My Citroen van, you just tell it you have filled up, not how much. With the ScanGauge you actually tell it how many gallons you put in (or should do). I have yet to run the ScanGauge for long enough to do a second fill up, but I am looking forward to seeing how accurate it is once I get to a third and subsequent top ups.
I must admit though, your figures for up and down hills seem wrong. There is a setting in the setup to correct DFCO errors.

Not in mine, as least as far as I remember. But as I said, mine's more than 10 years old, so newer ones might have more features.

This is the part from my manual.

http://ecomodder.com/forum/attachmen...1&d=1500567403