Gas Mileage Discrepancy Prius IV

That's so close as to be statistically insignificant. Even if the difference is real, any number of factors could cause such a small shift: terrain, wind, road surface, traffic, temperature. I wouldn't worry about it.

Tom

 

I'm not sure how you're calculating your mpg but it seems that the onboard display is at best an estimate and can't be relied on for accuracy.

The thread below has more information.

http://priuschat.com/forums/gen-iii...y/66149-2010-toyota-prius-fcd-inaccuracy.html

 

Did you reset the odometer at the beginning of each trip? (if the odometer was not reset, your return trip would actually be lower than 53.6 to have brought down the average.)

Even if its lower than 53.6, I agree that the difference is so small that it is probably not significant. However, one thing that could make quite a difference, everything else (weather, speed, traffic, etc.) being equal, is if there are more uphill climbs in one direction than the other. The inclines could be so slight that you don't even know you are going uphill, but the car does. See the thread:
http://priuschat.com/forums/gen-iii...ill-vs-downhill-makes-biggest-difference.html

 

Another mileage discrepancy that you'll find is that your ACTUAL mileage will not match your computer mileage. In most cases, your computer will overestimate it by 3-6%.

I just got back from the gas station 5 minutes ago. My computer read 54.8 mpg. My actual was 51.4.

And that's with a Gen II Prius. Give me a Gen III and I would be able to make magic. I digress.

 

We do a lot of testing on section of road that is slightly downhill going north with flat and uphill sections and uphill going south with flat and downhill sections. The average going north is 96 mpg and south is around 50 to 55 mpg. Add some headwind and forget it. Ours is a much more aerodynamic car than yours probably. This will impact your results greatly. Also, After 23,000 miles of testing I find the computer mileage to be very inaccurate. It is calculating based on some proprietary algorithms that we are likely to never get access to.

 

Florida has a hill?

 

I've driven routes in my car that seemed flat, while covering the same route on my bicycle makes it obvious which direction is up hill.

 

Through 13916 miles I recorded 294.115 gallons: 47.31 mpg. Displayed MPG before fill-up was consistently in the 51-52 MPG range. Best was an actual 436 mile trip @ a displayed 59.1 at fill-up was an actual 55.7. There is clearly a display error of ~6% better than actual. That seems excessively high to me.

 

J. Burns - You certainly have no complaints re fuel efficiency ... you are much better than the EPA figures. But I assume your question is, why the difference?

An earlier post suggested a variety of reasons why you could see a slight difference in your calculations. I agree. With over a years and 20,000 miles of experience with my G3 IV, I have documented slight variations in fuel efficiency due to temperature, and wind, and great variations due to traffic, speed, and topography. Not as well documented, is gasoline. ethenol is a factor .... might you have purchased gas on your trip?

I normally use cruise control as you mentioned. Here in the west, I get out of cruise control going downhill ... and practice a bit of hypermiling ... finding that "sweet spot" that cruise control cannot find. But in Florida, that may be a moot point.

I suppose after all is said and done, none of us can give you a valid answer why you experienced a difference. There are so many very small factors that the on-board computer samples, and makes adjustments. It could be as simple as how often were you caught behind an 18 wheeler? A recent mythbusters detailed the effect that a 18 wheel truck has on air dynamics .... it was tremendous!!

Hope you good fortunes continue. Enjoy.

 

I always get better gas mileage going South than I do going North, it is afterall, down hill...

 

deleted

 

I know wind makes a difference in mpg when I drive from South to North in the summer. This is an 80 mile round trip to work every day.

 

I have a 2010 Prius IV with almost 12,000 miles. My best mileage has been 43.9. I average 41 in every day traffic in the Ft. Lauderdale area. This is my 3rd Prius and gets the worst mileage. My dealer says it's the driver and I have to learn how to drive a Prius. DUH, I was getting 46 in Gen 2 models.

 

Maybe, it is high to you, but...

I also see 8-10% high on Honda and VW.

Ken@Japan

 

I noticed your previous posts also were mileage complaints.

It'd help to start a new thread answering most of the questions at http://priuschat.com/forums/gen-iii...-answer-these-questions-esp-if-youre-new.html. I don't think you'll be able to check the 12 V battery w/o a voltmeter or other tool.

If your driving is mostly city, it wouldn't surprise me if you get worse mileage than your 2nd gen. See Most fuel-efficient cars (3rd gen) vs. ConsumerReports.org - Most fuel-efficient cars (2nd gen).

 

The basic ingredient is topography, so your trip TO was slightly downhill overall. The return was slightly uphill, even if the highway looked flat. There are multiple other factors as already noted. I think your mileage was excellent. If you really want to get your hopes up (on a long trip) the car will be well warmed up, you are located at the top of a big hill, you fill with gas and then head down the hill driving conservatively. The MFD could show over 90 mpg, til you run out of hill! I do this all the time coming down the Sierra Nevada ( Rt 80/Reno to Sacto)

 

On the Gen III, is the bladder eliminated. To determine if the tank is actually full each time is impossible, on any car! But with a bladder it's even more questionable. Even 1/10 of a gallon could make a 2-3 mpg difference in the MFD and calculated.

 

have you tried disconnecting and reconnecting the negative battery terminal to reboot the computers?

 

YES, It is all in my post "Toyota Failure" I am trying to get a consensus on the validity of this procedure. It has worked for me, but this is only one man's opinion. Search, reboot, refresh.