I purchased my new 2006 Metallic Pearl w/o NAVI last Friday 04/20/2006, have 315 miles on it and plan to visit gas station within the next week or so. Early indications from my odometer are that I do a little better than the average in the database for this vehicle when I drive making high MPG my goal, and a little worse when I drive (faster) without regard for the MPG. I find the advice at this site usefull and will perhaps increase tire pressure from 32 PSI to 40 or 42 PSI in the future. I bought this car thinking that no hybrid ever got better than 80% of the EPA number, so I am very pleased to see initial numbers very close to the EPA estimate.

I plan to enter fuel useage data in the database. My question is, should I use the trip odometer MPG indication, or should I do it manually? Why does the forum give users a choice of entry method? I read in some posts that the odometer MPG computed number is very accurate, and I read in other posts that it is not accurate at all. It seems to me than a manual calculation would be the preferred method-miles driven divided by gallons to fill tank.

I assume MPG reporting here is on the honor system and we do not mail in gas receipts or video evidence of reported mileage. I also assume a tamper proof gas tap that would record and report to Jason any unauthorized fueling is not required. Just kidding.

I do seem to remember a practical joke some 20 or so years ago where friends added a gallon or two of gas at a time to an old fuel hog truck resulting in the owner bragging about its great gas mileage to the amusement of all.

It seems to me that the people that hang out at a site like this one (sorry to type cast) would be particularly succeptable to this sort of practical joke.

Comments?

Jon

 

Both methods of MPG reporting have issues. The displays tend to be optimistic. For example my display show 63.9 lifetime but calculations at the pump show 61.8. I think the pump method is more accurate in the long run so I use the pump method.

That said the pump method is not useful for compairing one tank to anohther unless you fill up to exactly the same level everytime, which is impossible. The display is better for compairing one tank to another.

The ultimate reporting method would be "hybrid" where you use adjusted display figures that are accurate for both tank comparisons and in the long run. The "hybrid" method is impossible to use in the short term because you need long term pump data. For example in my case the hybrid method would be to take 61.8/63.9 to get a correction factor of 96.7 percent. IMO the most accurate method would be to use the displayed value less 3.3%. Your correction will vary. I've been tempted to repost all the data using the hybrid method but have never got around to it, plus I don't want to lose the existing lifetime pump data.

 

Lake, I'm not so sure that's always the case. Granted, mine's only a little under two months old, but so far I've found that my computed mpg could actually be worse than what I'm getting. Thus far, using the trip A FCD for each tank, I've driven the 1669 miles at an average of 46.6mpg, using 35.8gal of gas. The trip B lifetime FCD is also showing 46.6. However, I've only put 34.5gal worth of gas into it, suggesting I'm really getting 48.4mpg. Now mind you, the pumps I use have the old-style wheel dials, but I do try to make sure I stop exactly on a tick mark since it's really the only way to get a meaningful number into my spreadsheet.

 

I haven't heard of any practical jokes like that (although in these days of high gas prices, the joke would probably be on the pranksters rather than the person making off with the free gas), but you could be right.

As for entering your mpg into the database, it's basically an honor system. Use whichever method you're comfortable with, if you're going to enter information at all. I have been so frustrated at times with the unreliability of the mileage meter that I no longer enter information in the database (although I keep track for my personal benefit).

I also felt that having that kind of tracking would make me very susceptible to fudging the numbers. Measurement is tricky- if you get a reading you like, you don't question it, but if you get something surprising or something you don't feel good about, you don't mention it, or you round it off, or you try to find some other way to measure it so that it comes out looking a little 'better.' Everyone does this, and not just with gas mileage- it's that the temptation is too great (no consequences for errors, and too small, but lots of little errors can add up to huge systematic errors in a database like this one) and it's too hard to avoid doing it.

So my advice, such as it is, would be to stick with one method that you determine in advance and then report the numbers you get as plainly as possible, without corrections or adjustments, because for the data to be useful to everyone, we have to try to be consistent. The meter saves effort, although it's only accurate to .4 mpg (so irksome!) but the problem with the other method is that it's easy to know how much you put into a tank but not so easy to know how much is in it at any given moment. The fuel gauge on the HCH is pretty inaccurate sometimes, I've found, and if the first bar or so takes 100 miles, the last three sometimes disappear in less than 40, for instance.

Good luck with the new car! Welcome to the forum, by the way, and I hope you enjoy looking around the place and getting cozy.

 

I have found that the display MPG is less than when you compute it with miles/gal of gas. When entering it on this site, I use the miles and gal. of gas option, while I wish that the site at least used 2 decimal places instead of rounding to one, it is good enough for me.

Some people get carried away with going to the same pump, same time of day etc, but I don't. This is the most I have ever kept track of MPG in a car and it is doing more than I could have hoped for so far.

I have my tires at 37psi or so, drive the speed limit, and try to anticipate stops etc and I have been doing pretty good. I love this car.

 

Speak for yourself.

I see no reason whatsover to fudge the numbers. To the contrary. The database is useful information for everyone, and I wouldn't want to corrupt it. What would I gain by fudging my numbers, other than knowing that I cheated and I don't have useful information?

 

I think on the long run, using miles and gallons will reflect a better picture of real MPG even if MPG indicator seem to be most of the time accurate. I personnally enter miles and gallons.

 

I enter using the gallons at the pump vs the displayed mileage. Like many here, I trip A to keep track of the tank and B to keep track of the "lifetime".

At each fill up, I find that trip A is anywhere from 1-3 mpg less than the manual calculation. I'm guessing that a large part of this is due to the differences in auto shut-off etc. The interesting thing is, over the life of my car so far (2500 miles), at my last fill-up, my trip B was exactly the same as my lifetime mpg in this database.

Contrary to my initial belief, maybe it is pretty accurate after all.

Dan

 

Elan,
I was speaking generally about the way human beings measure things, not trying to cast aspersions on our database, which I'm sure most people take as seriously as you seem to and which, hopefully, reflects a lot of effort and honesty by many people. But what I was talking about is empirically true- I could dig up some articles about studies that have been conducted to see how people measure things, and it's simply a fact: if you get what you expect, most people do not question it, they just put down the result and move on. If the result doesn't match their preconceptions, they try again and then again, or take other steps to arrange the way they measure it so that the answers come out 'right.' It's mostly an unconscious thing; we generally aren't even aware that we're doing it, but it is pretty well-established and is the reason for 'blind' and 'double blind' testing for many things.

The database is an aggregation of everyone's measurements, but having so many people taking them independently doesn't cancel out the little inevitable errors, because there's a very strong, unidirectional systemic bias: we all must WANT better fuel efficiency, or we wouldn't have bought hybrid cars, found this site, joined, and gone to the trouble of entering numbers in a database. It doesn't mean that anyone is dishonest, or anything like that. I was thinking about it mathematically, from the standpoint of someone who has gathered a lot of data in her time (back in my physics days) and offering a comment on that. And if you'll look again, my little suggestion was to pick a consistent measuring method to keep some error out of the system, because the measuring tools that we've been given to work with (fuel gauge, mpg meter) aren't the greatest, unfortunately- I'm not saying it's anyone's fault.

 

Grossly underinflated for FE purposes! Pump thos suckers up to 50!