The Great Mileage Experiment Ends

28 July 2005
10:29 PM

Since I got my new car slightly over a year ago, I have been tracking my fuel usage pretty closely. Every time I filled my tank, I would record the miles traveled and gallons used. When I had nothing better to do, I’d put the numbers into an Excel spreadsheet and see what came out.

I’m leaving for Chile in a couple days and won’t be driving my car for awhile (read: 30 months), so it’s time for a recap of fuel consumption in year one. Remember: you’re interested in this because I bought a VW Jetta with a diesel engine based on the assumption that it got great gas mileage and you want to know if that was stupid or what.

Without further ado, the numbers:
Total miles: 10,184 (I didn’t drive much while I was at school)
Fuel cost: $531.62
Lifetime average MPG: 40.2
Highest MPG for a full tank: 46.6
Lowest MPG for a full tank: 31.8 (75MPH + 40MPH headwind = 31.8MPG)
Most miles on a tank: 566

Pictures tell stories better, so here are two charts. This first chart plots fuel efficiency over time. The three major spikes are the three major highway trips I took: 1400 miles to and from school and 1000 miles to Atlanta, Georgia.


This second chart plots total mileage on the car over time. I didn’t keep any official record of how much I drove on the highway versus city driving, but from this chart you can see the times when total car mileage increased rapidly. That seems to coincide with how much I drove on the highway. You can see that the three sudden rises in this chart are correlated with a jump in fuel efficiency shown in the other chart.


And a few notes: When I got the car, I wrote about getting 46 MPG on the highway. While I didn’t routinely see numbers quite that high, I got at least 43 MPG when driving extensively on the highway. In the winter, my fuel efficiency dropped markedly. This is probably due to the cold weather, plus most of the driving I did at school was just short distances around town.

Regarding methodology: I reset the trip odometer every time I filled up at a gas station, which measures trips to the tenth of a mile. When I filled my tank, I wrote the total distance traveled on the gas receipt (which indicated total gallons pumped) and later put the information into an Excel spreadsheet that gave me the average mileage and other sundry statistics.