First 10,000 miles with my 2012 Prius

Trust me ... your fuelly calculations are the correct numbers ... car computer is at least 2-3 MPG high.


REV

 

I had a 2005 and now have a Pip, have always trusted the car's calculations. Because, When you tank up, you cannot trust the numbers on the pump and at what point do you KNOW, that means, certify, verify, guarantee.......etc that, the tank is FULL ??? You cannot. I imagine even in a Laboratory, it can be tricky.

 

So agree! Even if the numbers on the pump are correct, there's no way of knowing if the amount of gas that went in is actually the same as the amount of gas used from the last tank. The only way of knowing how much gas you started with is if you drained the tank to start with and added a pre-measured amount. With tanks this small, even a pint or two can throw the calculation off by a significant percentage.

I've only filled my 2012 three times so far. Twice the calculated MPG was higher than what the car reported on the MFD. This last time, calculated was lower than shown on the MFD. My guess is the car has it pretty close.

 

The best way is to do a running total for every fill. Total miles on car since new, divided by total gal's used since car was new. Keep a running total, only way to get best guess mileage.

 

This will get you your absolute best accuracy. Jabecker, the car computer is high. Trust us on that.

 

I've seen no empirical proof that the car is not correct. I've seen a bunch of people postulating that the car is high, based on anecdotal evidence, rumor, and hearsay.

There are all kinds of techniques used: "always fill until you can see the gas," "always fill to the first click (or second click)," etc., etc. None of those are accurate and all are open to way too many variables. And most are not even available here in Oregon, where we're not allowed to pump our own gas anyway.

Calculation techniques are "good enough." But not necessarily accurate. The only way to get an accurate MPG is to measure the actual amount of gas going into the engine while driving a measured distance. I don't have the tools to do that, and I'm guessing that most of the people on this forum don't either. The car has better information than I do. So I choose to believe it.

And at the last fill-up, the car was lower than the "calculated" MPG, not higher. (535 miles / 9.107 gal = 58.75 MPG -- car showed 56.4 MPG)

 

I had a 2005 for seven years tracked all gas and total miles. When I sold it I gave the new driver all my information. So I can not prove this to any one but Calculated for the life time was about 1-2 miles lower than what the car said.

 

Um, so everyone else on this site is wrong?

 

Almost everyone. What ever method turns you on is fine by me. It is not actually that important. If the car is high, good, I like high.

And, Trust Us, " The Recession is over"

 

No, Jabecker and I are right.

 

everyone is right, whatever floats your boat.

 

I get gas at the same gas station always filling to the first click. I think I am getting pretty accurate readings and is more accurate than the dash reading on my Prius.
There was an article last year from Edmunds - "Edmunds Testing Finds Overestimated MPG Is Common"
They did a couple tests across several vehicles and the gauges were 5.5% inaccurate on average.

Your Fuel Economy Gauge Is Fibbing - Edmunds.com

Most auto makers didn't respond to the tests and only one defended the gas gauge reading and mentions the biggest fluctuation occurs because of the ethanol in gas which contains less energy.

Last paragraph

"Whatever the reason for their inaccuracies, it seems that fuel economy gauges should have this label: "Your actual mileage may vary." And Dan Edmunds recommends using a second source for recording fuel economy, such as joining Fuelly.com and logging every tank of gas to get a more accurate reading. But for the technologically challenged, he recommends a hands-on approach. "Grab a pen and paper, keep track of the data yourself and come up with your own numbers."

I think it is very reasonable to be skeptical "Mr Empirical" of the accuracy of the MPG reading on the Toyota Prius.

 

If your guage normally runs around 50 mpg and this time is 42 or 57, then something has changed. You are doing worse or better. You can just use the guage to suggest where you are. That is very useful. For the actual do the old time calcs (and use Fuelly to track it)

Too much worrying about guage Inaccuracy I think. At least it seems consistent!

 

I'm going to collect a year's worth of data, but here is about 3k miles worth in my CTh -- same drivetrain as the G3 Prius:
Google Spreadsheet

As you can see, the car's meter is pretty precise at 4.7% +/- 1% (SD - 0.8%), but about 4.7% inaccurate lifetime.

 

I didn't realize the CTh has the exact same drivetrain. What accounts for the FE difference? Mainly aerodynamics and weight?

 

Markabele,

Heavier car, heavier suspension
215/17 inch tyres
0.28 drag

 

bet it's amazing inside though...you love it?

 

ahh,,,
I should first admit I am not a car guy. I bought the car as an upgraded Prius because the plastic creaks were annoying me in our G2, and twice a week I try to nap during a long trip when my wife drives. I thought the improved suspension would help me snooze. I also was worried that my wife would find the long drives hard on her back and wanted to snip that possibility in the bud. I probably should have just taken the time to disassemble the plastic to kill the creaks, and added a sway bar and fatter tyres to my G2. Or bought a G3 Prius with 6-way seats, but then the price difference was not that great.

It is a fine car -- don't get me wrong, just not that much better than a Prius. My greatest personal peeve is the upholstery. Customers can only choose vinyl or leather. Leather is a no-no in my home (even though I readily admit its advantages) and vinyl is ... vinyl. A very good vinyl no doubt, but still vinyl.

Compared to a G3 Prius stock, the handling is a joy discernable even by me.

 

Since the Edmunds testing used exactly the same inaccurate calculation method, it proves nothing.

Look... the car is probably off as well, because too many variables are uncontrolled. Here's just a few of the variables I'm talking about:
- The gas tank may have expanded or contracted due to heat/cold.
- The odometer may be (probably is) inaccurate for a number of reasons - tire wear, etc.
- The pump may have been serviced or adjusted between fill-ups. It may be inaccurate now, more accurate than before, or just feeling cranky today.
- The car's computer may not be accurately measuring the amount of gas delivered to the engine.

I could go on, but I think you get the drift. In order to have a truly accurate test, as many variables as possible would need to be taken out of the mix. You'd need an accurate way to measure the gas - probably an external tank that could be emptied prior to the test, filled with a measured amount of gas, and then emptied again at the end of the test. There should be an accurate way to measure the actual amount of gas delivered to the car - some kind of gauge between the external tank and the engine. The car would need to be driven for a distance that's been accurately measured by some method other than the car's odometer. The test could either be to (1) drive the car until it ran out of gas, measure how far it went (not via odometer), and calculate the MPG; or (2) drive the car for a measured distance (not via odometer), measure how much gas was used (comparing the gas left in the external tank with the measure to help ensure accuracy), and calculate MPG. The MPG from either test could then be compared to the car's calculation to see if it was accurate or not. I doubt that most drivers in this forum are going to those lengths to ensure accuracy.

Neither the car's computer nor the calculate from fill-up method are "accurate." But both methods are "good enough" to give a ball park estimate of MPG, and to compare relative MPG over time. And isn't that what most drivers want? I say use whichever method floats your boat. I just get irked at the assertion that the calculated method is more accurate, when really neither method is.

And that should be "Ms Empirical," thank you very much.