What accounts for this?

[hobba]

1. I am the only driver of the car.

Those are all valid questions. I tank up when I get down to one ot two pips. The AC is on all the time as FL weather requires. My commute is the same since purchasing the car new in Aug of 05. The car is serviced regularly by Toyota.

I imagine there really is no answer to be found here, other than the curiousity of why this happened after consistantly avg. 42-45 mph per tank.....

[CBarr31]

Hobba,

Those are similar swings which I occasionally see in Ema but regularly saw in my Corollas and 4-Runner, as I noted before and in previous posts. Your last 4 tanks seem "consistent" you might be out of the high/low rut as I call it.

Like I said before "Good Luck" finding an answer. I've seen this anomaly for more than a decade in 5 different vehicles and have talked about it with a dozen or more highly knowledge people and all we have got out of it is guesswork.

Enjoy driving and don't think about it to much or it will drive you nuts, LOL.

Chris

[richard schumacher]

Something changed to cause this. Eventually it will manifest in some more easily diagnosable fashion. Please let us know of developments.

[DaveinOlyWA]

looks like you are averaging 42 mpg. your wild fluctuations can probably be attributed to filling errors which are caused by faulty gas pumps (a study showed that the auto fill valve on 20% were defective) not filling to a consistent level.

now is this something new that is unique to the Pri? nope...its been going on as long as cars have been around. we used to contribute noticeable short tanks to "bad gas" etc... well, that was never the case because true bad gas would have most likely ruined the engine. we simply have more info and feedback on our driving performance.

based on your locale, you run AC, may be in a densely populated area, etc. so your mileage is not really all that bad. my dad averages the same as you do. he lives in Mission Texas which is a stones throw (if you are a girl) from Mexico. his mileage is bad, partially because he has degraded vision which causes him to drive without much anticipation....but then again, he had a 2005 Camry that barely made 20 mpg around town, so he is still doing much much better (his Pri is only a 2007)

a true comparison requires you to reset each tank as you fill it and record what the MPG's are as well

[hobba]

Thanks to everyone who weighed in on this subject. I guess there is no answer to why this happens or what has changed. I will keep an eye on it and if anything comes to light, I will share it with the group.

[DaveinOlyWA]

Originally Posted by hobba

Thanks to everyone who weighed in on this subject. I guess there is no answer to why this happens or what has changed. I will keep an eye on it and if anything comes to light, I will share it with the group.

actually there are several "possible" answers and the true answer is probably a combination of several things. you are doing all you can do and that is collecting data.

ultimately, its how much you take out of your wallet to keep from having to walk.

[ETP]

Originally Posted by hobba

My last dozen or so tankfuls have yielded wild variations in gas mileage. Every other tank is very low mileage or high mileage. For example, My most recent tankful claims 35.5 mpg based upon the Prius excel spreadsheet available on this web site. The MFD says I got 41.6 MPG, but I only drove 363 miles. My previous tankful was 48.3 based once again in the Excel spreadsheet. This has been the case for each of the the last 13 fillups. One being high, the next being low mileage. I did have the dealer reset the inclinometer the last time I had service, but it hasn't affected anything. My travel is unchanged as is my routing and use of AC which is constant here in FLA. The first three years of ownership, my mileage varied little or not at all. Anyone else share this experience?

Is it possible to steal gas out of a Prius. LOL

[hobba]

Here's a good example of what I'm talking about in this thread.

I recently made a daytrip from my home to Orlando, FL and back. Tanked up the car before leaving and did not top off. I drove to Orlando and when I got there, I found gas to be cheaper than at home, so I tanked up again without topping off. I drove home and again tanked up, same as before.

When I used the prius chat excel sheet to calulate my mileage, I averaged 46.7 on the trip up, and 30.1 on the trip back. All travel was done on the same day with AC.

Now I can understand a small variation, but this is ridiculous.......lol

[Rae Vynn]

Check the oil level. When you got your oil change, they may have overfilled it.

[Shawn Clark]

Earlier hobba stated: "The MPG as calculated by the MFD vs. the spreadsheet have varied by 0.2 to 0.4 MPG." Something is not right with this story as that is at least an order of magnitude less than the typical fill variation I've observed. I've had exactly one tank that showed only 0.4 mpg delta between the fill and the MFD. The median variation has been 2.3 mpg. And the standard deviation (if I throw out the one incomplete fill--car refused to fill) comes in at 2.4 mpg.

Also, the above doesn't mesh with the original post: "My most recent tankful claims 35.5 mpg based upon the Prius excel spreadsheet available on this web site. The MFD says I got 41.6 MPG, but I only drove 363 miles."