My on-board computer is consistently telling me 75-99 MPG on trips (usually 10 to 20 mile trips). Obviously that's wrong. Could this be a sign that some system in my car is faulty? Should I get it checked out at the dealer? I don't really care if the computer estimates are off, but am just worried that it could be a signal of something worse.
Depends on his driving style of course, but his readings would be way outside the norm range even accounting for the 5% or so split.
And what is your average mpg reading? Single trips can easily be in the ranges you quote if the conditions are right. It's your average mpg as displayed on your Trip A or B that counts.
I have done a 10klm 6 mile trip from the gas station I occasionally use to my house and had better then 50 klm/l (2l/100klm) or 120+ MPG means nothing. The trip is mostly down hill and flat. If I fill up then go up a long hill I can start a tank at less the 20MPG
original poster here. My average MPG between fillups is showing 65mpg. Hand calculating, I'm getting 45mpg. I'm not saying I should be getting 65mpg... just that if the computer calculation is way off, maybe something is wrong. I drive about 60/40% highway vs city. Typical driving habits, gradual acceleration, no hard braking.
The typical error in my experience is 5~10%. With OP getting 75-99 mpg results on relatively short trips, it sounds like something's wrong.
If you are regularly seeing 65mpg average mpg displayed on the trip meter and you are performing the hand calculations correctly and only coming up with 45mpg (number of miles driven divided by number of gallons pumped) then you have a problem and should take it to the dealer.
How many miles have you put on this car, and how many fillups have you made? If you have filled it only once or twice, I'd attribute the difference to less than full tank from the dealership, and to variations in refilling. But that problem cannot persist over more refills. The MPGs listed in your base post are quite certainly possible, under ideal conditions with the right skills. But they are highly unusual for a neophyte in ordinary conditions.
