I have a 2005 3.5S and have normally disregarded the fuel economy readings because they always seemed very optimistic. I hadn’t checked it against calculated mileage on more than one tank of gas until this week.
I filled the tank a couple of days before I left on a trip and zeroed the trip odometers and fuel economy display.
The first tank was approx 30% city and 70% highway driving. Fuel economy reading showed 24.4 mpg avg but calculated was 19.9 mpg (off by 23%).
Second tank was approx 95% highway and 5% city. Fuel economy reading was 28.8 mpg avg but calculated was 24.3 mpg (off by 19%).
Third tank was again approx 95% highway and 5% city. Fuel economy reading was 26.8 mpg avg and calculated was 26.5 (only off by 1%).
The tires are original and the size specified. I checked the odometer against highway mileage markers for a distance of 55 miles and it showed 54.1 miles so that’s less than 2 % off.
Is this normal?
Your calculated mileage could show a big swing because you are not filling it up to the same spot all the time. AS far as your odometer being off, check your tires. Are they the original tires? If not, then most likely they are a different size. Most people did not replace the tires with the correct size, because only one manufacturer was making them at the time.
Every time I calculate manually, it comes pretty close to the computer, like your third tank. Considering you are running the original tires, the only other thing I can think of is someone may have reset the computer in the middle of a tank without you knowing about it.
I would try 2 more tanks to see if the trend continues.
2004 Quest S
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