calculated vs. computer MPG - Please post your results

3500 miles and I seem to be hitting almost 56mpg conststantly on the display. Not sure if it's engine break-in or me just getting better at driving an "iPhone".

 

First fill-up, with a couple days of bump-and-go and then highway showed 54MPG on the display but 57 when I did the math. Really broke it in with 850 miles over the long weekend (picked it up with 2 miles on the odometer last week - all from me test driving it!). My neighbor has cautioned me that performance will go down over time, but I guess I'll see.

 

Your neighbor has it backwards. Mine has 3500 miles on her and the engine still isn't considered to be broken in. From everything I have read, it can take up to 10,000 miles after which you can expect to increase mpg by 10-15 percent. I also read a Consumer Reports (IIRC) and they compared their mpg numbers from a new Prius from 2004 to a 10 year old 2004 with over 200k miles with its original traction battery. The original 2004 got 40.4mpg and the one with 200k miles got 40.2mpg.

 

I've tracked my mileage carefully for over a year now--38 fill-ups and about 17,000 miles (and well after the engine's break-in period). The average MPG computed by the on-board technology has been 52.05 MPG, while the average I've calculated has been 49.68 MPG. That's just about a 5% overage on the Prius's part...

 

If it hasn't been said already because I'm not going thru 52 pages of posts to find out, use fuelly.com to post your mileage and get a true MPG average. But, make sure you don't top off your fill up's, stop filling after it clicks off the first time.

 

I have a 2011 Prius. There was a software recall last month and my mileage- per the trip set on the car, has dropped (city) to 37 MPG. I returned to the dealer and they reinstalled the software. Still the same reduction. Previously, I was getting 48 mpg in the city. I am now manually calculating the mileage to see what I get. This is all disturbing. I am wondering if the car read-out has been wrong for the past 3 years. I have 44,000 miles on my Prius.

 

Knowing whether the readout was correct is simple. How many miles did you typically drive between fill ups? An 11 mpg difference would be obvious if you followed any sort of pattern.

 

Manually calculating is the only way to truly see what your getting out of a tank of gas. The CON indicator on mine is almost always 5+% optimistic and has been as high as 9%. I stop at one click of the pump on every fillup but I would imagine from pump to pump there is going to be a variance. Even if you wait 2 clicks to top it off, 8 extra ounces of fuel is probably less than the difference of the rounding error from the CON.

 

Prius II went in for the recall, resulting in a serious drop in mpg. I took it back to the dealer, who had a factory guy on-premises that day. Apparently, the system will have to "re-learn" my driving habits to take it back to the upper-50s. Gradually there has been an improvement--'details at 11."

 

I have had my 2012 prius v for 4 weeks and now avg 59.0 mpg


iPhone ?

 

Over nine fill-ups my calculated MPG was about 2 mpg less than FCD MPG. Actually, I have thought the difference would be greater. We also own a 2012 Honda CRV. Its calculated vs. FCD MPG almost never varies by more than 0.2 mpg.

 

My calculated MPG over nine fill-ups is about 2 mpg less than the display. I had thought the difference would have been greater. We also own a 2012 Honda CRV. Its calculated and displayed mpg are almost always within 0.2 mpg.

 

I just did my first fill-up. The displayed mpg was 46.0 while the computed mpg was 52.1 (473.8 miles using 9.1 gallons). However, I do not top-off, so it's just whenever it shuts off on the slow setting. I imagine I might have been able to squeeze another gallon in, like I could with my van, which would have dropped the computed mpg down to 47ish. I figure if I refill the same way each time, future computed mpg averages should be more accurate. Unless one tops off, I don't see how the computed mpg can be accurate since there's no way to tell how sensitive each pump is. Does anyone know exactly how the displayed mpg is computed? Is there a flow-rate meter or something?

It was interesting to watch the reset display go from 31.9 to 72.8 for the 5-mile trip home. It won't stay on 72.8 for long once my wife gets in and turns the A/C back on and lead-foots it to her therapy appointment.

 

Oops! Removed,, wrong thread...

 

Mine too. Would be nice if there was a way to add a compensator in the settings to get it spot on.

 

Actually one fill-up before they updated my software my mpg fell to 39 mpg and has remained at that point. I've only checked it manually once, but it was about what the display was showing. I also have been getting less miles between fill-ups, so I really believe the car is getting less mpg. The dealer checked it with their laptop and said it was getting 52 mpg, but that really can not be correct.

 

My car always thinks it’s getting better mileage than it is. I haven’t recorded the estimates, but there have been some times when the read-out claimed I was getting more than 60 miles per gallon, and when I figured it out, it was only 58½ or so.

Whenever I go by one of those radar warnings that tells you your current speed, it’s always lower than what the car’s speedometer says, by two or three miles per hour (The warning sign says 30, the car says 32, say.). Ditto the GPS I borrowed for a couple of days from my son. The car thought it was going faster than the GPS did, by 2-7 m.p.h.

I supposed the two things could be related. Tire size differs from what has been programmed in? I assume it’s been programmed in.

I have new tires now, but haven’t passed by any of those radar things since I got them, so I don’t know if the speed is still off or not. But judging by all the jerks trying to ride up my tail, the speedometer is probably still reading higher than the actual speed.

 

It sounds plausible, but no. There's legislation to ensure the speedometer never reads lower than actual, or a little higher. Most manufacturers opt to err on the high side. The logic of the law is that you're never going faster than displayed.

The displayed mpg is another thing. The car (barring non-stock tires) has a fairly accurate odometer, that's also by legislation. So regardless of the displayed speed, it knows how much ground you're covering. And how much gas was used.

My 2 cents, it's very likely Toyota's exaggerating intentionally.