How do I calculate mileage on my 98 CRV 4WD?

[pnocti]

I was wondering how you guys can calculate your MPG to the exact decimal.

I guess the 1998 CRV does not have an MPG readout as the newer models.

For those without an MPG readout, how do you calculate it exactly?

I've read somewhere that you need to fill it up full tank and record your miles until your next full tank and then compute it from there.

Is there an easier way?

Thanks!

[lizzurd]

I was wondering how you guys can calculate your MPG to the exact decimal.

I guess the 1998 CRV does not have an MPG readout as the newer models.

For those without an MPG readout, how do you calculate it exactly?

I've read somewhere that you need to fill it up full tank and record your miles until your next full tank and then compute it from there.

Is there an easier way?

Thanks!

Divide the gallons used by the miles driven.

Or use something like this:

http://www.milesgallon.com/

[illegal]

on my civic it was easy, becasue of the 10 gallon tank :) I think the crv is a 15 gallon tank. So 300 miles divided by 15 gallons = 20mpg

[motoguy128]

on my civic it was easy, becasue of the 10 gallon tank :) I think the crv is a 15 gallon tank. So 300 miles divided by 15 gallons = 20mpg

So you always keep driving until the tank is empty? :D

[Radar24]

Assuming that the tank is refilled on the same pump at the same location and orientation, dividing a few hundred miles by gallons to a tenth of a gallon as indicated in the pump will result in MPG to a tenth or one decimal point of accuracy.

There are no shortcuts if you want accuracy.

But in reality what difference does it make if your MPG is 19.8 or 20 MPG?

It looks more accurate to show 19.75 but there really is not that much resolution. You would have to drive a 1000 miles since the ODO does not display tenths of a mile. For all intents and purposes 20.0 or even 20 is good enough. Round off if you use a calculator. Some of the newer Casios like the one I have will do it for you if you tell it to!

Does any one ever show MPG to a hundredth of an MPG? That would be a bit ridiculous. But then that is our job...:D

-Rg

[fillsteak]

I also have a gen 1. With every car I've owned, I keep a small pad of paper in the car (something like a 2x4 spiral notebook kind). I jot down the following with every fillup:

date-car's total mileage-gallons

So as an example, you'd have something like this:

9/01/09 - 30,000 - 10.15 gallons
9/11/09 - 30,333 - 12.00 gallons
9/21/09 - 30,650 - 11.52 gallons
9/30/09 - 31,114 - 10.73 gallons

So for the second date (can't start with the first) then you just subtract 30,333-30,000 (or simply 333) and divide by 12 gallons, which gives you 27.75mpg. I actually do this at the gas station and write that mpg on the gas receipt. The I have pretty much all the info I'd need.

I'd also suggest that if you aren't too interested in mpg over a single tank (never that accurate anyways), then go by a monthly basis and use the month's data. For the above example, you'd then take (month's miles driven)/(month's gas pumped).

So using those numbers, you'd take (31,114-30,000)/(12.00+11.52+10.73), which gives (1,114 miles)/(34.25 gallons) = 32.52mpg. So over a month, the 32mpg is more accurate over the single 27mpg instance. Of course, other factors come into play, but if you do this for a year, you'll get a pretty accurate estimate of your mpg. The numbers I just made up, btw... I don't get this high of an mpg.

To make life easy, you can always use the trip-ometer and keep resetting that with every gas fill. Then you just take that and divide by the gallons.

Good luck!

[Radar24]

Nice and easy example by the numbers :) fillsteak. Sometimes we take too many things for granted. Since I have been doing pretty much what you describe except on a permanent record in a bound approx 6" by 8" notebook. I would lose the slips! Not spiral bound as the pages rip out after a while. I actually draw lines and label the top line on every page. About twenty pages later (I skip some) I start my maintenance log. That way I can look for trends in MPG that indicate something is wrong. The maintenance summaries are all in one notebook along with the MPG and anything else I add to the tank such as injector cleaner is noted in the MPG log on its own line. That way I do not do it too often or wait too long in-between on the injector cleaner.

Future car buyers like to see all that info too!

How anal can you possibly get! Oh well…

I used to have a problem with getting my wife to do it regularly. She would procrastinate and forget. But after many many many...repeated request she now does it regularly too. My kids used to do it while driving my cars but have now drifted away from regular MPG records on their own cars. When they complain about drivability problems I tell them I do not have the data so I cannot help then. I can be cruel that way sometimes. :D Not really! I eventually help them out after giving them a hard time. They got my number though so a hard time does not really work to get them to write down the MPG data at every fill up. Right at the gas station before leaving. :mad:

Spreading out the calculations over a period of timer will definitely give you a better average. But never to hundreds or 27.75 as you indicated. There are just too many variables for that accuracy to mean anything. Rounding that off to 27.8 is good enough IMO. Any more accuracy to hundreds or 27.75 is meaningless if you do the number and accuracy analysis. That is in general the calculation cannot have any more meaningful accuracy than the number with the smallest accuracy. Even if the gallons are displayed to five decimal places such as 12.345 gallons on the pump. That would be like 333 miles driven or to three decimal places. Likewise 12.3 gallons is actually good enough. That is why I round off to 27.8 MPG. For some reason out of habit I suppose I write the gallons to hundreds or 12.34. Go figure!

It might even be debatable that rounding off to 28 is good enough but I still like to get it to one decimal point or three total decimal places. I’m not sure that spreading out the number over many fill ups will increase the number of relevant decimal places beyond three. It has been too long since my number theory courses. Ahhhh! (Yawn!) Getting a little on the boring side?

Suit yourself. Whatever rocks your boat. :) Do it to five place such as 12.345 if you want to. The important thing is to do it IMO.

I hope I have not complicated it any further pnocti. It is really very easy. Other than the accuracy and meaningful decimal places comment, Fillsteak’s example is excellent and by the numbers.

-Rg

[pnocti]

Thank you all :)

[fillsteak]

I forgot to mention, for even an even easier time, you can purchase and install an external device and let that calculate the mpg for you. I have one, but find that the mpg isn't very accurate. It is decent enough, however, if you are just looking for a ballpark range.

Here's a ScanGauge II, which reads from your ODBII:

http://www.amazon.com/ScanGauge-Compact-Multifunction-Computer-Customizable/dp/B000AAMY86/ref=sr_1_1?ie=UTF8&s=automotive&qid=1253822830&sr=8-1

It also reads codes if your CEL is on... useful to have.

[fujisawa]

Easier way! :D

fill the tank completely. reset trip odometer.
drive until >1/2 is gone.
fill again, and write the trip odo reading on the recipt next to the gallons; reset the odo.

then you have a recipt with both the gallons used and the miles travelled since the last fillup. divide one by the other and voila.

the key is to remember to reset the odo every time you fill up. i often forget, and then it's a wasted tank from a calculation perspective.

and none of these methods is perfectly accurate; if you hit like 37mpg you've made an error somewhere like not totally filling the tank. so you have to not rely on any ONE receipt. but i mean, the new onboard MPG meters aren't that accurate either, so it's all a tossup.