Recently I drove 800 miles through 15F to 35F, dry air and was able to monitor my mileage. Instead of the usual 53 MPG @ 65 miles per hour, I was running 49 MPG or worse at temperatures below freezing. Thanks to Ken@Japan who provided the air densities at different temperatures, I was able to put this spreadsheet together:

TempF TempC density_kg/m3 %_density MPG
15 -9.4 1.34 111.7% 47.5
32 0 1.29 107.5% 49.3
68 20 1.20 100.0% 53.0
85 29 1.17 97.5% 54.4

There was good agreement with the air density changes and MFD displayed mileage. The MFD has a horizontal scale line at 50 MPG so it was easy to see the pattern.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
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