Your Fuel Economy Gauge Is Fibbing: Edmunds Testing Finds Overestimated MPG Is Common

I guess this is the norm...our '06 G6 was always high. Our '10 Equinox is always high. And my Cruze is always high. I wish they were more accurate. And yes, just to clarify, I fill up at the same place 90% of the time, and wait for the same pump most of the time. Method, lock handle to slowest flow rate until it clicks off, then I manually go slowly to one more click. Have done this for years.

I do wish they were more accurate, I use them mainly as an indicator, then subtract about 10%.

I don't know what to make of this at all. I don't pay attention to the MPG on the DIC but i reset it with fuel used. It said 12.6 gal used when I filled up today and the pump clicked exactly at 12.6. The last couple times I've been able to squeeze a lot more fuel after the click. This is the third straight time my light came on at exactly 12.6 gal, which makes me think the tank is 12.6 gal for all models with 3 gal of "reserve." I don't understand if it draws fuel from the reserve though...?

Yep, that's why I have a ScanGauge II. Much more accurate, oftentimes jibing exactly with the pump or 1 to 2 tenths of a gallon off.

On our Honda, enough people complained for long enough where Honda reprogrammed the MPG computer to be more accurate. It's typically within a half of a MPG of actual fuel economy now instead of 10% high like it used to be.

is it possible that onstar can update the computer remotely to fix this over compensation?

I just ask because of all these threads about lower mpg than previous trips...
Im one of those. The DIC was showing about 3-4mpg higher than if I did the ol fashion math method. Now, they are spot on.

I've read on other places on and off this forum that the concensus seems to be that the DIC mpg is about 3% too high. So if you're showing 38mpg, then you're truly getting. 36.86. In my experience, the 3% off seems to be fairy accurate.

Edit: What is interesting is that the 3% too high of a reading will of course differ depending on what your mpg reads. 3% of say 30 mpg is going to be different than 42 mpg. But whatever, it still seems to be spot on with me.

of course, you have to actually use the 1 click method to accurately compare. I for one just try to haul as much fuel in there as possible

sciphi said:

Yep, that's why I have a ScanGauge II. Much more accurate, oftentimes jibing exactly with the pump or 1 to 2 tenths of a gallon off.

On our Honda, enough people complained for long enough where Honda reprogrammed the MPG computer to be more accurate. It's typically within a half of a MPG of actual fuel economy now instead of 10% high like it used to be.

Click to expand...

What year? Cause Honda also got their peepee slapped for an over reading odometer.

But to the topic I would never really put touch faith into the MPG calculations when a known miles traveled / gallons used is usually dead on




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ErikBEggs said:

I don't know what to make of this at all. I don't pay attention to the MPG on the DIC but i reset it with fuel used. It said 12.6 gal used when I filled up today and the pump clicked exactly at 12.6. The last couple times I've been able to squeeze a lot more fuel after the click. This is the third straight time my light came on at exactly 12.6 gal, which makes me think the tank is 12.6 gal for all models with 3 gal of "reserve." I don't understand if it draws fuel from the reserve though...?

Click to expand...

This is what gets me as well...last fillup, DIC said I'd used 12.1 gallons, the Low Fuel Warning just came on as I arrived at the pump island. I proceeded to (one click method) put 13.3 gallons into the tank.

I drove 456 miles on that fillup:
Calculated: 456 miles/13.314 gallons = 34.249mpg.
DIC Numbers: 456 miles/12.1 gallons = 37.7mpg.

DIC Estimate was 37.6mpg. So....is it calculating correctly but measuring fuel consumption WRONG....that appears to be the case....the algorithm for fuel economy is probably the simple one we use. Distance is measured correctly, but consumption.....'nother story, IMO...

...5% error is what I've found and been posting here.

...and, "No," On-Star™ cannot "flash-update" the BCM (Body Control Module).

As I have mentioned before, the DIC is more accurate the more conservative you drive, which only makes sense, usually the margin for error increases as you move toward the upper limits of a system.

I down shift a lot, coast and almost never WOT. My DIC is usually within at least .3, if not spot on. Of late, it reads lower than my actual, as I have increased the amount of coasts and downshifts that I do.

The DIC is a great indicator of how aggressive you drive or accelerate, the greater your margin of error, the more aggressive you are over someone who is spot on or within .3. Which is also why you may not achieve the MPG you are looking for.

Only 6 fillups so far, but the DIC in my Eco is pretty far off: 8-10%. And we drive quite conservatively.

70AARCUDA said:

...
...and, "No," On-Star™ cannot "flash-update" the BCM (Body Control Module).

Click to expand...

"ok", "thanks"

lol

I found the 3-5% error as well. BUT I found the error to be less the more I baby the car. IE, if I get 37DIC on my ECO because I have been driving aggressive, it might be 35 calculated. Last 2 tanks I drove more carefully and was only off .5MPG each time @40MPG. I would assume that when you put your foot in it the engine is using way more fuel than the computer thinks.

feh said:

Only 6 fillups so far, but the DIC in my Eco is pretty far off: 8-10%. And we drive quite conservatively.

Click to expand...

^^ Me too...I really am trying to see what the car will get economy-wise. Driving really conservatively. My LTZ seems to read about 8-10% high.

Just got home from a 500 mile trip. DIC says average was 36.8 mpg. Actual math based on fill up showed 34. I'm still happy

be careful of over filling after the pump shuts off as this can mess up the fuel gauge sensor in the tank causing it to go farther than it was designed for and also cause problems with the emission system by getting fuel in the lines.

...here's how our 2011 LTZ DIC-numbers compare with our gas-pump numbers:

http://www.cruzetalk.com/forum/27-f...ed-dic-vs-gallons-used-fill-up.html#post31075

Interestingly though, my best tank on fuelly hand calculated was 37.2 MPG on a road trip. The DIC told me 36.5 MPG. I literally went gas station to highway to cruise control to gas station. Maybe the DIC screws up when you accelerate?

And the whole reserve thing throws me off. 12.6 on the DIC and my pump cuts off EXACTLY at 12.6 every time. Light comes on at 12.6 every time. This is supposed to be 15.6 wth! I'm somehow able to squeeze an extra gal til I see the fuel coming up and personally I'd rather squeeze in as much as possible since I hate frequent fuel stops/

After checking with seven tanks, I found a 3% difference. Most of my driving is highway.