Tom, do you normally "top off" the tank, or do you stop when the pump turns off the first time? I never top off.

Topping off can mess up you calculations, among other bad and awful things it can do.

Read up on all the enviro info if you are curious about the dangers of topping off the tank, but it WILL mess up your calcuations. If you top off, you are lowering your calculated MPG, which does what? That's correct, it makes your calculated MPG move "farther away" from the FCD.

Not topping off is my best guess as to why my calcs are so close to the FCD.

 

No, I rarely top off the gas. I do give it a two or three more clicks. I'll try to just stop at the first click and see how it goes.

But why would adding fuel by topping off lower milage. I can see it for one tank, but the added fuel would make the next tank appear to have better milage and over time would even out the numbers. The added fuel doesn't magical dissapear.

 

does not lower mileage - lowers your MILEAGE CALCULATION by falsely increasing the gallons used, which will lower the MPG for that tank......

Because when you "top off" you never can know that you put "exactly the same amount when I topped off the last tank" whereas if you NEVER top off, you always know that you stop at the same place.

 

My point is the calculations should even out over time. I would get lower milage on one tank and higher on the next. But they dont.

 

Yes, I admit that it is frustrating to never be "on the money" and I supposed I am unclear as to why you are 10% off versus FCD. That's a big diff...

I think you might be able to reduce the difference by starting a new pattern of never topping off though.....

 

It seems that those of us in this thread that see the biggest variance have 2003's. I'd like to hear from more people on this. I'm guessing it's something they fixed for '04.

 

i have an '04 hch and dont have this problem (overestimating by at most 1-2 mpg)
i thought maybe the odometer was off? but it matches the exact distance that mapquest gives for my daily route, so it cant be.

 

I'm pretty sure it has to do with the calulation Honda must be using (injector duty cycle & fuel pressure & built-in odometer I'm guessing). My guess is that the OEM FPR is cheap (relatively speaking) and small deviations in fuel pressure will lead to this anomoly. I'm sure honda could nail the consumption side of the equation if they had a very accurate fuel pressure sensor.

The other half of the equation (distance traveled) is a LOT more tricky without something like the aforementioned GPS integrated into the mix.

I'll live with 2 simple tactics:
1) Calibrate your odometer on the highway when your satisfied with your tire pressure
2) Track the "pump delivered" fuel into your car over time knowing that its the most accurate thing you've got going without busting out a graduated cylinder at fuel-up time

... then corroborate your long-term statistics.

I'm doing all this in a spreadsheet, but reporting on this site with the "dashboard stats" so everyone is comparing apples to apples.

 

My HCH is a 2005 and is consistantly optomistic. The car is getting 58.2 mpg lifetime calculated at the pump but the trip "B" lifetime display shows 60.5 mpg which makes it about 4% off. Of course the display jumps in 3 or 4 tenth increments so the 60.5 figure could actually be anywhere from 60.1 to 60.9. I wish the display kept track in tenths.

 

I'd say 4% is pretty darn near acceptable, especially since station pump accuracy has to be somewhat variable. I'll take 4% any day over the 7-10% I see.

I calculated one tank at 50.1 when the comp said 55.4!

Can you imagine? The horror. The horror!