Full tank = 400 miles @ 50MPG Why?? :(

Here is another vote for the bladder! If it is good enough for NASCAR...it's good enough for me. Sure it is a bit funky to fill sometimes, but much, much safer in the event of a crash.

 

Till it pukes gas back at you after filling.

 

The display on the LCD screen says I am getting 50 MPG but the fill up and the math say I am actually getting 2-3 mpg less than the Prius says I am. I have filled up twice since purchasing the car and it is roughly the same in both cases.
Has anyone else noticed that the display is overly optimistic?
Also, what is the Gen 3 that I have read in some of the responses. I own a 2009 Prius.
Thanks
Bill

 

I hope you are trying to perform the typical hand calculation method used on regular cars without a bladder system. Have you read this yet Bill? And this one for sure.

 

Short answer: You don't have enough data to know whether the info on the display is "overly optimistic." The gas tank's bladder really prevents you from filling to the same point each time. This means you cannot rely on having one fill exactly (or even closely) match the amount of gasoline used to get the mileage delta from the prior fill to the current one.

Long answer: Do a search through the PC forums to find the nearly endless list of threads addressing this issue.

My response: I'm approaching 30,000 miles on my 2007, so I think I'm getting to the point where my collected information is fairly good (i.e., reliable). For the lifetime of ownership, I see that the MFD calculations are higher than the "gasoline purchased" calculations by just more than 1 MPG. I don't know that the information I have tells me that one method is better than the other, but I do tend to believe the car's calculated use of gasoline more than I believe the dealer pumps. If we used weight calculations as opposed to volume calculations, I might feel differently. Beyond that, I don't know that pumps with such high-volume delivery and frequency-of-use demands are going to be designed for dependable accuracy as much as dependable delivery. (More to the point, I don't think they will be designed to allow the +/- to balance at zero, but at a point favoring the seller of the product.)

Your 2009 is a G2 or Gen 2 or second generation (U.S.) Prius. The Gen 3 will arrive within two weeks as the 2010 Prius.

 

The accumulated error in my first 7,300 miles has been -0.89% (more used than indicated by the MFD). It was randomly bounding around zero or a little above until cold weather hit, then went negative rapidly. When warm weather arrived again it leveled out.

 

Perhaps the pumps have been set to measure volume at standard temperature and pressure, and the calibration happens seasonally. This could account for the variation. The other option is the change in "bang" that comes from seasonal variation in gasoline blends and additives.

 

This has no affect on the bladder ...but.....fuel quality makes a difference on mileage and you don't always know what your really getting ,no matter where or how often you get gas .. old gas or mistakes in mix from suppliers ,ie gasahol or other % mixes...all make a difference ....so tire pressure ,wind, fuel quality,brand of tire,load occupancy ,cold, all make a difference and they change often................

 

So very true. Not that it conquers such variations, but nothing beats a lot of data to establish a better read of a car's performance. One "bad" tank of gas out of four is a much greater distortion than one out of forty.

 

If that was the source, then the effect would be reversed of what I'm seeing. (It would result in less metered from the pump than what actually entered the tank.) Instead, I suspect that the fuel is colder in the car's gas tank on average and this results in the injector calculation coming up short by ~1% in cold weather. AFAIK the vehicle is not reading the gasoline temp, so the factor for the injector pulse will be fixed for a given temp.

I believe gas pump meters are mass flow measuring (compensating to 60 F gallons according to an Omega site), and that fuel injectors are not, because the injector is not temperature compensating. The injector is a volumetric device if I understand correctly.