Effects of Terrain (Region) on Mileage
Active Enthusiast
Joined: May 2006
Posts: 231
From: Calgary, AB Canada
Re: Effects of Terrain (Region) on Mileage
I should be so lucky. 
I would expect vehicles at sea level like yourself to get better mileage than someone like me.
My commute is 12.96 miles but elevations vary between 3,503' and 3,956'
I would expect vehicles at sea level like yourself to get better mileage than someone like me.
My commute is 12.96 miles but elevations vary between 3,503' and 3,956'
Active Enthusiast
Joined: May 2006
Posts: 215
From: Southern California
Re: Effects of Terrain (Region) on Mileage
While the car's engine works harder going uphill than it does going down, the swing in MPG might also be due to the slope of the gas in the tank when you are going uphill versus down. When you are going uphill, the gas sloshes to the back of the tank and, depending on where the sensor is located, the car is fooled into thinking you have more (or less) gas than you really have. If it thinks you have more gas, the the calculated mileage statistics (on the dash) will show an increased efficiency.
The gauges range from being a little inaccurate to very innacurate.
Best to take the miles per tank and divide by the gas station's meter to determine mileage.
Anything else (gauges and dials in car) is guesstimates, at best.
The gauges range from being a little inaccurate to very innacurate.
Best to take the miles per tank and divide by the gas station's meter to determine mileage.
Anything else (gauges and dials in car) is guesstimates, at best.
I have found the MFD to be very accurate. I'm sure you're not familiar with the grapevine. There is a large increase in elevation to reach the summit and then you drive for quite a few miles before descending. I took readings when the car was at level spots so you're idea that it was the slope was not a factor. It looks at fuel consumed not at level in the tank.
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Enthusiast
Joined: May 2008
Posts: 25
From: South East Michigan
Re: Effects of Terrain (Region) on Mileage
I choose another route home yesterday. (This is my 40 mile one way commute I do twice a week.) Thanks to the elevation map, I noticed another route that doesn't drop down 300 feet in the middle of the commute. On nearly a half tank, according to the Fuel computer, I am at 40 MPG exactly.
Thanks for posting that elevation map!
Thanks for posting that elevation map!
Driving in stealth mode
Joined: Aug 2007
Posts: 430
From: Far South Chicago Burbs
Re: Effects of Terrain (Region) on Mileage
No problem. I am glad to finally return the helps as so many others have helped me. I never paid attention to the hills until I got my TCH.
Ridiculously Active Enthusiast
Joined: Aug 2006
Posts: 859
From: Waterloo, ON
Re: Effects of Terrain (Region) on Mileage
My understanding is that the fuel usage is computed by the engine ECU from the fuel-injector pulse data. The amount of fuel injected per pulse is known by the ECU. The FE in mpg (or the FC in L/100 km) is then computed from the amount of fuel used and distance covered. The fuel tank gauge, and its (in)accuracy, play no role in this computation.
Stan
Stan
Old Boomer Techie
Joined: Jun 2007
Posts: 572
From: Pacific Northwest (WA)
Re: Effects of Terrain (Region) on Mileage
My understanding is that the fuel usage is computed by the engine ECU from the fuel-injector pulse data. The amount of fuel injected per pulse is known by the ECU. The FE in mpg (or the FC in L/100 km) is then computed from the amount of fuel used and distance covered. The fuel tank gauge, and its (in)accuracy, play no role in this computation.
Stan
Stan
Correct! The same technique has been used in general aviation piston powered aircraft that are fuel injected for many years. The only difference is that the fuel used is related to time and expressed as Gallons per Hour (GPH) or, for diesels or other aircraft that use Jet A, Pounds per Hour (PPH). This is then used with the caluclated ground speed to calculate range remaining, usually in Nautical Miles (NM). The accuracy can be quite good, and is actually required by regulations to be within 2%.
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