weird mileage concerns

[JackDodge]

I've had my Prius for several months now and am not sure what's going on with my mileage. The very first tank, I got around 50 mpg and what was on the display matched what I got on the calculator. One time, I let the tank runk down to empty and filled up at 573 miles. The display said I was averaging 55 but the calculator showed I only got 51. The next tank, I topped it off, needing only 7 gallons and the calculator said I got 56 mpg while the display said I was getting 52. I went in to the dealership to get my first oil change last weekend. I had already put several hundred miles on that tank but wasn't paying much attention to mileage other than the display telling me I was averaging 52. Yesterday, I suddenly realized that the fuel gauge showed almost empty because the car beeped at me and flashed that last little square. That happened when the trip was showing mileage at 473 which seemed awfully low to me. I filled it up later that night and was startled when the pump shut off at only 7 gallons but after checking, it was obvious that the tank was full. Why would the gauge show almost empty, did the dealership reset something that threw off the gauge from what was actually in the tank? Also, the display said I was getting 52 and the calculator said I was getting 65! I can't actually be getting that can I? But then the numbers don't lie but I'm having a tough time figuring out what's going on here.

[DaveinOlyWA]

sorry see nothing wrong with your stats. dont worry about individual tanks. keep lifetime stats and base your driving on a combination of what you normally average, current MFD reading for your tank, and the bars you have left on the gauge.

also, although, not certain (there is a lot of posts that mention it though) when going through major temperature changes, the capacity seems to change too. most seem to get less capacity in their tanks as the temps drop. couple that with the move to winter formula gas (which has less gas in each gallon) and tank averages will be dramatically different

[Spunky]

Bought our Prius in early August and haven't noticed any problems when filling her gas tank. However, we don't keep close tabs on tank mileages and just refill whenever there are only two "boxes" lit on the fuel indicator.

Some have notice fuel bladder issues and discussed them on this site.

We haven't noticed any problems with back pressure while fueling up, but there have been reports of such.

[alsgameroom]

I have to agree with just worry about lifetime mpg not tankful.

The amount of fill has to do with the bladder in the tank.

You can not keep short term accurate measurements when the tank does not fill to the same point every time.

My last fillup... 2 bars left... took only 6.6 gallons.

I didn't think at the time after the pump clicked to put it on slow or medium until it clicked again. I just paid and left .

I then thought she must have not taken a full tank...but it was weird because the tank read full and the first bar did not disappear until around 120 miles... she always does this.

[skruse]

As with others I only fill up when the last cell is blinking. I only put in 10.0 gallons. This minimizes fuel stops and makes calculating cumulative fuel efficiency very easy. I keep track using Excel and keep a current paper copy in the glove compartment (handy for sharing with nonPrius owners when there are questions). While knowing the current tank fuel efficiency is nice, place your emphasis on the cumulative or long-term fuel economy. You will have a much better sense of the health and performance of your Prius.

I too become concerned when a single tank fuel economy decreases. When I fill up again, the cumulative fuel economy puts things in long-term perspective. On occasion, due to traffic and road conditions, I cannot drive in my normal frugal manner. When I take a "hit" I work diligently on the next tank to protect the cumulative fuel efficiency.

[hdrygas]

Bloomfield Hills MI hmm. What has the weather been like? I no longer live in the Midwest but in a more temperate climate but we are clearly into the fall/winter season (not much difference between either fall/winter or spring for that matter) the temps are down and as I have the Scan Gage, so I can track the engine temps, I am now very aware of how much longer it takes for the car to get up to the temp to be in full hybrid mode. In my am commute it takes about .5 to .75 more miles to get at full hybrid mode at 50 F. It is going to get worse when we are in the mid 40's. I grew up in Ohio and went to school in Hillsdale MI. It is going to get much colder where you are! Your milage will drop. The Prius is about reducing emissions. That is "job one" for the Prius. It is going to keep the car and the catalytic converter at optimal temperatures, if you want a bit of heat for your self it will cost you!!! Getting the car up to temp will burn fuel just to heat it up. Wait till summer you will do far better than me! My summer temps are in the mid 70's for the highs! 50's to low 60's in the am. I will never get the m.p.g. you will in the summer. It is a give and take imagine the hit folks it Alaska and Canada take in the winter!

[JackDodge]

Thanks for putting it in to perspective, everyone. I've been stressing about this for several weeks now because I was paying attention to the mileage of all of my previous Toyotas since I can remember and I was always able to get consistency. This car has been a new experience but it was unnerving when the gauge showed empty when I must have had four or five gallons left. If I actually got 65 I must be doing something right.

We've been overcast, a little drizzily and temperatures between low 50s and low 60s all week, hdrygas. A fellow Prius driver told me that I'd better think about getting a good set of tires before winter sets in and I got that tire comparison from another post so hopefully the winter will be fairly uneventful.