Not all gas pumps are spot on either; some states have a running battle with pump makers and gas stations trying to keep the accuracy close to where it should be.
How accurate is GM's mpg computer?
- Thread starter Blue_Goose
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All these variables add up, that's why I always sincerely doubt it when people claim they've seen a 0.5 mpg increase the last two tankfulls just because they did X, or some other such statement. They just don't really know that for a fact. After many, many tankfulls, sure, you might be able to discern a difference.
Hermann
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MPG readout on our Mercury Mariner V-6 is very accurate. We reset it every oil change to see MPG trends over the 5 month period of each 5K OCI. Every time I have checked manually on a individual tank the numbers are very close, 1/2 MPG or so. Now if the mileage would only improve, It $uck$.
Happy motoring to all!
Happy motoring to all!
There are so many variables to account for that are not ....
I just laugh when people speak of their vehicle's fuel economy - esp. when it gets compared to another user across time and distance .
Here is another variable - not commonly discussed or accounted for .
From a much longer article here ;
http://www.
consumeraffairs.com/news04/2006/12/hot_fuel.html
" - For decades, fuel retailers have been selling gasoline or diesel that is warmer than the industry standard of 60 degrees.
Like all liquids, the volume of fuel expands and contracts when the temperature changes. Hotter fuel has less energy in each gallon than cooler fuel. Regardless of whether fuel temperature rises due to radiant heat from the sun or the refinery process, the results are the same: consumers pay more for less energy.
Those who buy fuel in bulk, such as the U.S. armed forces, have temperature-adjusted purchase agreements with the oil industry. In fact, fuel is adjusted for temperature all along the distribution line except at the end point, when it is delivered to individual consumers.
With U.S. retail pumps, motorists never know how much energy they will receive from a gallon of motor fuel. -"
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The only thing I'm really sure of with accuracy is how many dollars are put in the tank .
Even odometers can be more than you think - just consider incorrect tire pressure over 150k with a slightly different installed height from a slightly different aspect ratio - tread width .
Most people have no clue that there is just as much and more often than not , more screw ups and screw overs in the POL group as there is by the automotive OEMs .
That includes a great deal of 'warranty effects' as well.
Puts a little different light on the pretty much universal cold temp fuel economy drop story as well , although all the hows and whys ......
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I've wondered this as well. My new Fusion has a Message Center. For City Driving, it has been dead on with my calculations. On the one highway trip, it registered about 1.5 MPG higher. Now I'm thinking: I never top fuel off anymore. Each pump will shut off at different times. Is the computer really more accurate?
Yeah , its really not clear as to what is accurate when and how and why .... and then there is all the 'uniqueness' of each situation ...... how many variables are 'off' and how they interact - and how different vehicles respond in similiar situations .
Its crude and I offer no justification but on credible reporting ( a topic in itself ) I 'listen' to everybodies numbers and figure plus or minus 10% - sometimes on some specific powertrain combinations you have to adjust differently - 'kick' it downward and/or widen the plus or minus .
Its crude and I offer no justification but on credible reporting ( a topic in itself ) I 'listen' to everybodies numbers and figure plus or minus 10% - sometimes on some specific powertrain combinations you have to adjust differently - 'kick' it downward and/or widen the plus or minus .
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How do you know? I will trust the sensors over most peoples calculations. The flow sensors monitor how much fuel is used and they also can tell many miles have been driven with pretty good accuracy. The flow sensors are probably just as accurate as gas pumps.
JTK
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Joel
Yeah, I don't really know how it works but I always just assumed it based the amount of fuel used on the pulse widths of the fuel injectors x their flow rate.
Uh, what I just said?
Sorry you posted that at the same time that I was posting, so I didn't see your explanation.
It could be what you said, but I was also told that they monitor the difference between the fuel feed and the return line. Either method would probably be more accurate than the manual calculation method.
I suppose, but the newest GM's have a return-less fuel system, so I'd imagine they're only be monitoring the supply.
same pump, same station goes a long way to ensure accuracy of fillups
of course this is not always possible, ie road trips...and then the other variables such as temperature thermal expansion, etc...but all in all, it's not really that hard to be pretty accurate if one tries
The computer has no way of monitoring the fuel flowing through the line. It calculated fuel based on how much it puts in the engine. Remember, the computer knows this, because it DETERMINES how much fuel goes into the engine, via injector pulse width.
We measured the difference on our last trip in our Park Avenue. Computer:28.3 Me:28.6
Seems pretty close to me. We also were usually within 1 mpg on our 87 Riviera.
-T
We measured the difference on our last trip in our Park Avenue. Computer:28.3 Me:28.6
Seems pretty close to me. We also were usually within 1 mpg on our 87 Riviera.
-T
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