Fuel Mileage - Car Computer vs Manually Calculated
Thread Starter
Intermediate
Joined: Dec 2013
Posts: 385
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From: PA
Fuel Mileage - Car Computer vs Manually Calculated
Anyone else noticed the computer vs trip computer mileage is consistently different? I still use the old fashion way of calculating MPG. Mileage since last fill-up/Gallons. I have consistently calculated 1.5 to 2 MPG over what the car computer calculates. This is over at least 15 fill-ups and I go two hose bump offs past first kick-off when refueling. I can understand if it was a few fill-ups but this is consistent over many tank fill-ups.
On another note, on highway, warmer weather, in normal mode, non-aggressive, I get 25 to 27 MPGs depending on how many hills I encounter.
And just to avoid the wise responses, yes, I know how to do division, sometimes I even use my toes.
On another note, on highway, warmer weather, in normal mode, non-aggressive, I get 25 to 27 MPGs depending on how many hills I encounter.
And just to avoid the wise responses, yes, I know how to do division, sometimes I even use my toes.
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Joined: Dec 2001
Posts: 562
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From: ATX
I've noticed that my since refill vs resetting the calc doesn't match. I've also noticed that if I push the mileage rather than refilling when I get a low tank warning the mileage calculator starts climbing.
Driver
Joined: Mar 2008
Posts: 54
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From: GA
I was just going to start a thread with this same topic. I've only checked once but my calculated MPG was about 2 mpg greater than the Since Last Fill Up showed. I guess they figure that no one is going to complain about getting better mileage than what the computer shows. 
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Joined: Jun 2014
Posts: 82
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From: CA
The pump calculation is not accurate for a single fill-up due to the differences in shut-off levels from pump to pump. If you keep logs, that will average out over time, giving you an accurate number. I've filled my GSh up 10 times, so I've got pretty good data.
As for the the computed MPG, you have the two numbers, Average, and Since Last Fill-up. My observation is that the Average seems to be a moving average, which you can reset. I have to take the Since Last Fill-up for what it says it is. With my GSh, both computed MPG numbers are 1-2 MPG higher than my calculation at the pump.
As for the the computed MPG, you have the two numbers, Average, and Since Last Fill-up. My observation is that the Average seems to be a moving average, which you can reset. I have to take the Since Last Fill-up for what it says it is. With my GSh, both computed MPG numbers are 1-2 MPG higher than my calculation at the pump.
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Thread Starter
Intermediate
Joined: Dec 2013
Posts: 385
Likes: 19
From: PA
The question is how does the computer calculate the number of gallons used? Where is that number coming from? I am not a physics expert, so can't tell you is temperature or other factors impact volume of the fuel tank.
I always fill it up, but how does the computer react to partial fill-ups?
As mentioned by the previous poster, my calculations is over at least 15 fill-ups. And consistently it is 1.5 to 2 MPG off. I am assuming the discrepancy is accounted for by "filling the gas to exactly the same level" which is unlikely.
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TonyES350
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Jul 10, 2006 03:41 AM
