mine is only about 2-3 % overestimating my mileage (shows 47.6 when i really got 46.4 mpg from calculating by distance traveled/gallons used)

could it be that the disparity varies with driving style and location?

 

Granted. That's pretty good, but you have a 2004. tbaleno and I have 2003's. I wonder if this problem varies with the model year?

It fit's my conspiracy theory. 2003 is the debut year for the HCH. Maybe they decided to *tweak* the computer by just a little so the early adopters would be just a little more jazzed about their car. If anyone complains, "What's the big deal?"

I only halfway believe in the conspiracy. It's probably just bad engineering.

 

Over the 9000 miles of my 2005, mine has almost always been within 0.5 to 1 mpg (once it was 1.3 mpg off). Always on the optimistic side.

My first inclination was to claim consipiracy on Honda's part, but then I began to wonder who I trusted more: the pumps themselves, which are calibrated but allowed to be off by a certain amount -- or Honda. I'm not quite sure the answer to that question, but it does make me wonder if the HCH estimates are in fact accurate, and there is another reason for the discrepancy (evaporation, miserly pumps, or something else).

I mean, it really does seem that it would be terribly easy to calculate the value correctly. If anything, I would guess that it was the fluid measurement piece that is amiss, rather than the software. Unless it IS a conspiracly, of course.

 

My mpg has been off too. I started seeing a 7-10% error, it was close to 15% happy on my last tank. My current reading on 560 miles is 52.9, I'm probably more around 46 mpg. Has anyone written Honda about this? It's frustrating, but it's still nice to be concerned about getting 45mpg as compared to 53mpg.

 

I know the Civic doesn't have NAVI, but here are my thoughts on MPG calculation. Most important, I believe, are the thoughts in bold, which someone mentioned earlier:

Thoughts for using NAVI for mileage calculation: (1) NAVI appears to figure mileage via GPS - it always says a bit more in mileage than the odo. I tested it with my Garmin GPS, and the Navi and Garmin were the same - the odo differed. So, where does you opinion lie with the accuracy of GPS? Many people differ, but my opinion (limited, though it is) from what I've read is that the GPS is more accurate. There are speed discrepancies in speedometers - that's undeniable - which would seem to affect the accuracy of the odo. Also, tread depth, to a slight degree, and how many turns you make. Some have changed tires and/or wheels - are they *exact*? (2) Has anyone seen the reports that are issued on the accuracy of gas pumps? There is an entity that checks their accuracy from time to time and they are rarily exact. They are certainly close (usually), but not right on. They sometimes publish these in our local paper.

 

I agree its probably at the pumps.

Take a look at this interesting thing I found.

Lets use an example figure if you drove 550 miles showing 51.4 on your odometer put in 11.7 gallons as the pump measured.

11.7 47.41

Now look at how much gas you should have bought to be in compliance with what the car is reporting.

10.7 51.4

Interesting that you would need pretty close to 10% more gas.

My question now is this. Are the people reporting descrepencies using pzev(sp?) or the ULEV versions. I'm using ULEV.

What part of the country are people from? Maybe some states have stricter laws governing how much the pumps can be off by.

I'm from Illinois.

 

Good question. My HCH, which is usually off by 1 mpg, is the AT-PZEV version.

 

my mileage differs by around 1 mpg too and i have a 2004 SULEV-Zero Evaporative Emissions (same thing as AT-PZEV..really..)

 

Interesting read:

http://www.spitzerandboyes.com/Ezine/flow31r.htm

 

Thanks, tbaleno! That was interesting - never thought about temp volume changes. Another point goes to car reading accuracy.