Real MPG vs Trip computer
- Thread starter Jays07MS3
- Start date
I've now got about 10,700 miles on my MS3, and have experience driving it both purely highway (Boston to Wisconsin, then Wisconsin to LA) and mostly city (LA). I had seen other posts like this thread mentioning the optimistic trip computer MPG, so I have paid attention. Here's what I've observed.
During pure highway driving (1-2 stops per tank), the trip computer is dead on, within 0.2 MPG. I was getting 29.8 to 31.0 doing 75-80 mph; 340-350 miles per tank wasn't a problem. My girlfriend's Mazda 3 2.0L sedan only got 29 highway during a road trip this summer!Auto vs. manual perhaps?
In the city, I've been averaging just about 290-300 per tank, for an average of ~25 MPG, while my trip computer is saying 26.5-27.8. I too noticed the ~2 MPG optimism since moving to an urban area.
My theory is similar to chronus337 in that the stop and go part is what causes the difference to occur. Look again at the CUR MPG on the trip computer at a stop light. It doesn't read zero; it reads "--.--". Since it's not a number, it doesn't average it into the trip computer's average MPG. It basically ignores whenever you are at a stop. But since you are still burning gas, the calculated fuel economy will be better than actual.
Anybody want to time how long they have the engine running but aren't driving during their next tank of gas? Also, does anybody know the fuel burn rate at idle? Then we could figure out if my theory is true....
-Carl
Nice theory. Its possible thats correct but I don't think it is for my car. I've only taken one road trip and that was from San Diego to Vegas. It took almost exactly 1 tank each way. If you look at my numbers for 9/5 and 9/7 you'll see those fill ups, one before I left and one after I got home. I only stopped once and that was on the way there and my house is directly off the freeway and there was no traffic either way. The trip computer was still off by 2.32 and 2.65. If idling time was a factor then I would expect both of these numbers to be a lot different.
And the reason my gas mileage wasn't better was because I averaged about 90-95 mph the whole way (drive2) (we travelled at night
)Damn engineer.... couldnt let me live in my ignorant bliss thinking my trip computer was accurate... and you just HAD to go and throw real data to back it up... damn you!
P.S> Im an engineer too so I have a right to give you crap... so what kind of engineer are you btw?
P.S> Im an engineer too so I have a right to give you crap... so what kind of engineer are you btw?
My 'average' mpg has went down from idling for about 10 mins in a parking lot, so I think it takes it into account. Still it may be inaccurate, or something. I think it's either this or it does not give accurate data while giving it full gas a lot.
<-- engineer in training.....lol
<-- engineer in training.....lol
Damn engineer.... couldnt let me live in my ignorant bliss thinking my trip computer was accurate... and you just HAD to go and throw real data to back it up... damn you!
P.S> Im an engineer too so I have a right to give you crap... so what kind of engineer are you btw?
LOL! I know I ruined it for myself too. I didn't start doing manual calculation for the first 5 or so tanks. So the whole time I though the computer was accurate and that I was getting 27mpg.
And I'm currently a process development engineer. But that mainly entails mechanical, test, and software engineering.
