Trip MPG vs All Time MPG

No. There is only one MPG calculator, and that shows the MPG since it was last reset, whether that be the last trip, or the last tank. If you want to know the lifetime MPG, you will need to keep records. Entering them on a place like CleanMPG will make the record keeping easy, and the calculation automatic.

 

F.Y.I. We keep an Auto Log book and a pen in the glove compartment. Can be purchased at any place office supplies are sold. We log every tank fill since new. Date, odometer reading, miles/tank, gallons, cost, & $/gal. The log book has a quick mpg table in the back that we use on occasion to also log the mpg. It is really easy. Once you make it a habit, it just becomes second nature and dosen't take that much time. Whether you choose it enter it into a spreadsheet or not, you will always have the detail should you choose to do so. We also keep every maintence or service invoice. These may not add a $ value on resale but will help make your vehicle more marketable, assuming you took good care of it. That's how I can also monitor any changes in mpg over time. That's how I noticed the affects of E10 here in Georgia, and changes in mpg that seemed to follow switching to Mobil1 and increasing tire pressure, as well as fine tuning driving habits. Without keeping some type of log, anyone claiming to know what kind of mileage they are getting under varying circumstances, is anecdotal at best. Keeping the log by fillup, allows you to use your MFD on trips, if you like, to monitor the overall mpg for your trip. Enjoy.

 

If I'm not mistaken, when the 12V battery is disconnected (e.g. for maintenance service) that also resets the MPG calculator and resets to zero the number of miles driven since the last fill-up. i.e. it works the same way as if you pushed the Reset button manually.

Hence the surest way is to maintain a log yourself.

 

I reset it at every fillup. If you don't, it doesn't change much after one or two tanks, and is pretty much useless. I keep a small booklet in the glovebox, with a mechanical pencil (pens freeze here in the winter and refuse to write). I put my own columns in the book:-
Date--mileage per odometer--distance traveled--fuel used--l/100 km(mileage)
Some like to add cost of fuel as well.
In Canada the govt. gives out cardboard slide rules that calculate the mileage. I have a few of these, and they also make it easy to convert to MPG Imperial, if you really want to know that. I also carry a circular slide rule for when I travel in the US (conversion from US gal to litres).

 

Zen is correct - when I had my DRL installed it was reset to 0. This is likely to happen (reset accidently or by servicing the car) many times during the life of the car thus another reason why it is better to keep manual records.

 

Wow! It's really a breath of fresh air to know someone who knows what a slide rule is, let alone still uses one. I have several and used them extensively before the hand held calculators came out. Still have my 6" & 10" K&E's. Neatest one I ever saw though was about a 6" or 8 " cylindrical that was the equivalant of something like a 6 footer.

You're probably one of the few people that would have gotten my meaning on an earlier post when I compared the accuracy of mpg calculations using gallons pumped instead of gallons used to trying to read a 6" slide rule to 4 decimal places. I'll have to go dig mine out and dust it off. Thanks for the memories.

 

Well, I use the slide rule in the car because the batteries don't freeze/die. But you do have to be careful if the rule is cold. It's plastic and gets brittle when its' cold. Best part is it was free - from Motorola Semiconductors.

 

Point well taken. I'll have to dig my 6" out for the glove box.

 

My slide rule is only a few feet from where I'm sitting right now...

 

After looking at many of the other questions about MPG and finding a few charts/Excell docs kindly posted by users, I created my own version (most that I saw were MPG and nor L/KM which is better for me) and use the MFD to measure lifetime average, workout the tank average from the amount of fuel added (yes not very precise due to the bladder) and also take a median average just to see what happens.

Unfortunately I've only refilled once (damned Prius just won't guzzle down that fuel ) but hopefully this should give me some nice answers and not just pretty graphs.

I read on the site that as the feul gage is actually a guessometer it may be best to work out your mileage by the amount of fuel added at the end of a tank and distance travelled...

 

Don't forget that most pumps these days will print out a receipt for you. The receipt has just about everything you need on it except for your mileage since last reset. I keep an envelope and pen in the glove box and jot down my miles (total odometer miles and trip miles) and MFD MPG on the receipt before reseting the Prius MPG calculation and trip odometer. Then at my convienience I enter the data at www.greenhybrid.com and compare the calculated (miles driven/gallons pumped) vs. MFD MPG. They are usually pretty close.

Weirdo

 

I essentially do the same. I've had my 2008/pkg2 Prius since September 2007, and initially did not reset the MPG reading on the Consumption screen, as I wanted to retain the cumulative MPG from acquisition of the car. That went south when I inadvertently reset both measures of mileage and MPG on one fill-up.

Since then I have gotten into the habit of resetting the Consumption screen at every fill-up. This also gives me the benefit of knowing exactly how many gallons, at a minimum, I should be able to pump aboard, simply by dividing the Consumption screen mileage reading by the MPG reading prior to re-filling. Since the MPG figure is usually close to 50 mpg, the mental arithmetic is easy, by doubling the top figure and shifting the decimal point 2 places, If I cannot get at least that amount into the tank, something is wrong with the tank bladder.

That may or may not be the maximum tank capacity, depending on whether or not the prior fuelling maxed out the tank capacity. In addition I keep the printed receipt and record the ODO reading. This enables me to keep a spreadsheet of cumulative fuel consumption and variations since day one.

 

The precision of the slide rule drops from 3 or 4 figures to only 2 or 3 when your wearing gloves . I loved my old slide rule but when the price of an electronic calculator that would square and add to memory dropped to only $225 dollars I bailed out.

I've had the log book in every car I've owned so far. On our new Prius my wife and I will share the car (whoever has the longest commute for the day gets it. She has told me I can keep the log if I want but she will not. With incomplete data it's not going to do much good so I'll have to depend on the screen.

 

Anyone ever have the pleasure of using a, I believe it was a Marchant, 4 function mechanical desktop calculating machine. It could add, subtract, multiply and divide. It looked like the old cash registers or adding machines. It had 12 columns of 0 to 9. The last 2 were after the decimal. It had a carriage on the top that displayed the results mechanically. Point being, I used to relieve frustration on occasion by dividing 22/7, the fraction I use for government work, when whenever I'm using doesn't have I Pi constant. It would sit there for 15-20 seconds whirring, churning, clanking and escaping. My co-workers, were not as enthused, since it was a small clerical bullpen, and it was loud and distracting.
Yeh! Young and annoying 20 year old.

 

I used one a few times. A marvel in it's day but it was a bit dated when I encountered it. I think a college mate had one he used for his accounting assignments. This in days before $15 calculators.

 

Yea, I remember those electro-mechanical monsters, except that as a Sales Engineer at Douglas Aircraft at the time (late 60s) we had Friden desk calculators for the most part, very similar to the Marchant machines. I swear those things weighed upwards of 50 lbs and yes they were loud, distracting and sometimes destructive, when the clanking carriage pushed stuff off the desk that just happened to be in its path!

What a change in 40 years eh!