How accurate is that trip computer at calculating fuel economy?
I have constructed a database to verify this (available for downloading) and based on 359 tanks of gas all recorded to the nearest tenth of a gallon in my logbook (5000 gallons), the trip computer agrees with the gas pumps to a degree of accuracy greater than 8 gallons in 5000 over time (see the graph). I suspect some of the variability stems from temperature fluctuation causing changes in the volume of the fuel and heavy air conditioning usage appears to affect the trip computer somewhat. I am still investigating this. It appears the trip computer may slightly underestimate fuel usage in cold weather in the city and slightly overestimate fuel usage in warm weather on the highway based on the trends I’m seeing. Or perhaps I’m seeing an accumulation of rounding errors since I only record my fillups to the nearest tenth of a gallon. In either case, the trip computer is very accurate tank-to-tank.
