sx sonic
New member
This is intended to become a comprehensive thread for any and all things MPG, or Miles Per Gallon related.
The goal is to compile information in one place to answer MPG concerns, questions, tips to improve it, and understanding your DIC (info display).
Feel free to add suggestions that would benefit these posts.
-1st post will contain the basics of fuel economy, calculating MPG, and the DIC
-The 2nd post will be about conditions that affect MPG.
-3rd post will cover tips and supply some links
-4th post will have a "help checklist" for people to use if they have MPG concerns.
MPG or Miles Per Gallon is the standard measure of fuel economy in the U.S. In other words how far a vehicle can go for a given amount of fuel. It is determined by taking the miles driven and dividing by gallons of fuel used.
For example lets say you drove 400 miles and used 10 gallons of gas. Divide miles driven by gallons used and that's your gas mileage or 400mi/10gal= 40mpg.
That's the hand calculated way or hand calc for short, and is the standard for real world comparison; outside of the "scientific" EPA tests.
Hand Calculating MPG
The "ideal" way to do this is to reset the trip odometer at fuel up. -Drive until the tank nears empty (or as close to empty as you feel comfortable). -Fill the tank to full and calculate the MPG. -Repeat the process. The same pump should be used each time and the tank should only be filled until the pump kicks off, no squeezing in extra fuel.
That method is extremely accurate. It's also very picky. The most reasonable accurate way to check MPG is to follow the above steps but not worry so much about what pump is used, or squeezing in a few extra squirts of gas. It's still accurate but be aware that calculations can vary slightly.
For instance lets say you drive the same 400 miles only this time you stop at a new station and/or top off the tank and the pump says you put in 10.5gallons, that's 38.09 MPG. Or if another pump reads 9.5 gallons, that's 42.11 MPG. The differences probably aren't going to be off that much, but it is a very real example of how the exact same fuel consumption/trip can show slightly different calculated MPG.
DIC/Display calculation of MPG
How about the DIC, or MPG display on the car? Thanks to technology it is very easy to view your MPG without spending time at the pump calculating it yourself.
While it's a wonderful tool for watching gas mileage, it does have some pitfalls. At it's best it is almost as accurate as hand calculating MPG, but not as repeatable. Typically it's off 1-3 mpg, occasionally being off a good bit more, and on occasion accurate or optimistic of real gas mileage.
The DIC computes gas mileage by putting injector opening (fuel used), speed sensors (distance traveled), and some other sensors thru an algorithm and calculating MPG. Because of all the variables involved when making cars/sensors/electronics it is just impossible to make the DIC as accurate as the hand calc method.
Now there's a few ways to use the DIC and each has it's own perks and shortcomings.
Resetting the DIC each fill-up-
This method is simply resetting the MPG display at fill-up and not resetting until the next refueling. It's the closest to actual hand calculated results. It is also the most reflective measure of real world fuel consumption (aside from hand calculated).
Again what's displayed must be taken with a grain of salt, as it's typically a few mpg optimistic of actual fuel usage.
Resetting the DIC while driving (Rolling Reset)
A rolling reset is simply resetting the MPG display while you're driving, such as cruising down the interstate, accelerating, coasting down a hill, etc.
Rolling resets can be very useful for learning what driving styles result in the best mpg. Drive a certain speed, reset it and see the result. Then drive a different speed, reset the DIC and see how it compares. Or try different shift points or acceleration and reset between the different styles and see what gives the best results.
The downside of this method is that it is not accurate of holistic gas mileage, it's just a snap shot of fuel consumption. Rolling resets are almost always going to be substantially higher than what actual tank mpg calculates out to.
Never resting the DIC or rarely resetting it
This can be used to track a lifetime MPG average. The downside of this method is it takes a long time to show changes in gas mileage. The longer between resets the slower the display will take to change. This method does not do show tank to tank differences and if you've never reset the DIC it's likely that it will read lower MPGs. It also becomes inaccurate when lots of miles have been driven without a reset.
For discussions and comparisons it is desirable and important to list how you track your mileage. Otherwise it is impossible to determine the accuracy or validity of reported MPG.
For example two people report they get 40 mpg. One person hand calculates mpg and the other is figured by the DIC doing a rolling reset. The person that stated they got 40 mpg doing a rolling reset is not even close to getting 40 mpg over a tank.
The goal is to compile information in one place to answer MPG concerns, questions, tips to improve it, and understanding your DIC (info display).
Feel free to add suggestions that would benefit these posts.
-1st post will contain the basics of fuel economy, calculating MPG, and the DIC
-The 2nd post will be about conditions that affect MPG.
-3rd post will cover tips and supply some links
-4th post will have a "help checklist" for people to use if they have MPG concerns.
MPG or Miles Per Gallon is the standard measure of fuel economy in the U.S. In other words how far a vehicle can go for a given amount of fuel. It is determined by taking the miles driven and dividing by gallons of fuel used.
For example lets say you drove 400 miles and used 10 gallons of gas. Divide miles driven by gallons used and that's your gas mileage or 400mi/10gal= 40mpg.
That's the hand calculated way or hand calc for short, and is the standard for real world comparison; outside of the "scientific" EPA tests.
Hand Calculating MPG
The "ideal" way to do this is to reset the trip odometer at fuel up. -Drive until the tank nears empty (or as close to empty as you feel comfortable). -Fill the tank to full and calculate the MPG. -Repeat the process. The same pump should be used each time and the tank should only be filled until the pump kicks off, no squeezing in extra fuel.
That method is extremely accurate. It's also very picky. The most reasonable accurate way to check MPG is to follow the above steps but not worry so much about what pump is used, or squeezing in a few extra squirts of gas. It's still accurate but be aware that calculations can vary slightly.
For instance lets say you drive the same 400 miles only this time you stop at a new station and/or top off the tank and the pump says you put in 10.5gallons, that's 38.09 MPG. Or if another pump reads 9.5 gallons, that's 42.11 MPG. The differences probably aren't going to be off that much, but it is a very real example of how the exact same fuel consumption/trip can show slightly different calculated MPG.
DIC/Display calculation of MPG
How about the DIC, or MPG display on the car? Thanks to technology it is very easy to view your MPG without spending time at the pump calculating it yourself.
While it's a wonderful tool for watching gas mileage, it does have some pitfalls. At it's best it is almost as accurate as hand calculating MPG, but not as repeatable. Typically it's off 1-3 mpg, occasionally being off a good bit more, and on occasion accurate or optimistic of real gas mileage.
The DIC computes gas mileage by putting injector opening (fuel used), speed sensors (distance traveled), and some other sensors thru an algorithm and calculating MPG. Because of all the variables involved when making cars/sensors/electronics it is just impossible to make the DIC as accurate as the hand calc method.
Now there's a few ways to use the DIC and each has it's own perks and shortcomings.
Resetting the DIC each fill-up-
This method is simply resetting the MPG display at fill-up and not resetting until the next refueling. It's the closest to actual hand calculated results. It is also the most reflective measure of real world fuel consumption (aside from hand calculated).
Again what's displayed must be taken with a grain of salt, as it's typically a few mpg optimistic of actual fuel usage.
Resetting the DIC while driving (Rolling Reset)
A rolling reset is simply resetting the MPG display while you're driving, such as cruising down the interstate, accelerating, coasting down a hill, etc.
Rolling resets can be very useful for learning what driving styles result in the best mpg. Drive a certain speed, reset it and see the result. Then drive a different speed, reset the DIC and see how it compares. Or try different shift points or acceleration and reset between the different styles and see what gives the best results.
The downside of this method is that it is not accurate of holistic gas mileage, it's just a snap shot of fuel consumption. Rolling resets are almost always going to be substantially higher than what actual tank mpg calculates out to.
Never resting the DIC or rarely resetting it
This can be used to track a lifetime MPG average. The downside of this method is it takes a long time to show changes in gas mileage. The longer between resets the slower the display will take to change. This method does not do show tank to tank differences and if you've never reset the DIC it's likely that it will read lower MPGs. It also becomes inaccurate when lots of miles have been driven without a reset.
For discussions and comparisons it is desirable and important to list how you track your mileage. Otherwise it is impossible to determine the accuracy or validity of reported MPG.
For example two people report they get 40 mpg. One person hand calculates mpg and the other is figured by the DIC doing a rolling reset. The person that stated they got 40 mpg doing a rolling reset is not even close to getting 40 mpg over a tank.
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