My Prius MPG seems to be too high

You're seeing the effects of the bladder in the gas tank. ;-)

HTC Evo 3D

 

The gen 2 Prius in North America (2004 - 2009) has a rubber bladder inside the gas tank. This badder is of variable size and folds oddly at times.

Living in MS I got between 7 and 11 gallons on full tanks, depending largely on outside temperature at the instant I was refilling. However the internal folding process can also alter the size in a fashion that cannot be predicted. (by me)

I recommend averaging mileage over many tanks. Fuelly - Track and Compare Your MPG will help.

 

isap,

It is better if you calculate your gas mileage over several tanks of fuel. As pointed out the bladder does affect the amount of fuel it takes to fill up. The bladder shrinks when it is cold and expands when it is warm. I suggest you calculate your MPG over a minimum of five (5) tanks of fuel to establish a baseline average. Fuelly.com is excellent for keeping a average for you.

Also, when the bladder does what happened to you on this fill up, chances are the next fill up the numbers will go the other way. It is normal with the US model Gen II Prius.

I note you are new to the forum. With that said I must say "Welcome to Prius Chat"!

 

Right, that was LAST FILL. Since the refill volume of Prius tank (with bladder) is so highly variable, the mileage traveled on this previous fill is not necessarily well correlated to your current refill volume.

Ok, so this figure should correlate with your miles at your NEXT refill (assuming you refill at about the same one bar remaining point).

Of course it's also difficult to refill at exactly the same point (same remaining fuel) each time, so either way you'll have trouble in obtaining a truly accurate measure from a single tank full. You've got to track over multiple tankfuls to really get a meaningful result.

 

isap,

Remember that temperature plus other factors do affect the way the bladder works. As it has been pointed out, doing a single tank for mileage purposes really doesn't mean anything. I can show you references of what you have pointed out. There are several occasions of the same thing in our records for our Prius also. What you reported is typical of the Prius with the bladder. What is important is the overall average, and not one single tank.

Register at fuelly.com and record your fill ups there. Over time you will get a better idea of what your actual mileage is. Furthermore the Prius like all cars gives it best mileage during the summer and gives it worst mileage during the winter. That is why they say YMMV.

Best of luck to you, and once again "Welcome to Prius Chat".

 

If you take off about 3 mpg from the MFD readout you will find your calculated figure after a few tank refills will be close to this figure. The MFD readout is optimistic on the number of mpg the car actually achieves.

John (Britprus)

 

have the same problem with my bladder.

 

What you can do is get your fuel up receipt and then write on it when you get your next fuel up how many miles you went by the time you hit 1/10.

I am placing my receipts into the little cubby under the cd player so I can do this each time. I had 4/10 when I picked up the car and went 166 miles. The fill up was 7.6 gal, it's cold, so I presumed the fuel tank is gonna accept a little less.

 

The bladder affect will really show in the winter. Also, beware of winter gasoline. The 2nd Gen Prius seems to be very prone to losing mileage due to the lower heat value of winter gas. The flammability goes up and the BTU's drop, since its cold you got to have gas that will easily start so the flame will ignite with less effort.
It will get better if the temp rises during the winter or you are lucky enough to live in the Southern US where the temp may go below 32 but not stay there for days on end. We in the Midwest see temp swings of better than 50 degrees. A week ago Monday, it was 19 when I got up in the AM. By Sunday, it was up to 70 degrees. Now think about gasoline that will work in that kind of temp range. Then, to have a car that will start with any kind of gas that you can pump into it. We should thank the engineers that put fuel injection and the computer into our modern day vehicles.

 

I just noticed that actually... Our temp hit 20 and below, staying there, when snow dropped last Tuesday, and my mpg has gone into a nosedive. Hovering around 44, 4/10 left now I'm at 42.8. Was used to 51 the first month driving this beautiful machine

 

Fuelly.com is a great site for keeping track of your mpg. You just sign up and log in everytime you fill up. You just enter how many miles you went since your last fillup and how many gallons you got. It keeps a running total of your mpg and makes charts for you.

 

I only get 288 miles from a tank.. how do you get 525!?!

My MFD says I'm getting 47.5 mpg... no way!!

 

With the bladder now I am seeing it fill up, can't get any more fuel to pump, and the pips only fill to 8 or 9. I seem to lose those initial two very fast. For example from 1 pip /330 miles I only got 5.3 gallon fill and had 9 pips. After 120 miles I was at 5 pips there. So the actual bars representing the fuel are subject to estimating on the bladder effect, I think. 45 mpg average right now with snowy conditions that sometimes mean slow going on the freeway