Drove 540 miles with still two pips left on the fuel guage in the MFD. MFD read 64.5 (with only the last 450 miles tracked .. I had cleared the MPG reading when the ODO reading was about 110 miles). Apparently, I must have done real bad on the first 110 miles, since the pump MPG number that I calculated was about 55 MPG.

I know that there might be some discrepancy in the values that MFD displays and the number at the pump .. but this is too big a difference ..

Regardless, I am happy that I could get the combined Hwy/City EPA's MPG mark on my first tank. It probably might be also attributed to the warm temperatures of Houston (80-90). I wonder whether the Prius's efficiency will see a detirioration when the temp. climbs above 100?? Anyone has any data on that?

Anyways. Just wanted to let those of you who doubt on Prius' performance know that I did get the EPA numbers on my first tank, and it makes me tremendously pleased!

The bladder in the Prius tank is not as 'deterministic' as ordinary tanks. You can get considerable variation in each tank but over time, the errors average out. These variations can be as much as a gallon.

Feel free to take a peek at my mileage chart to see how bad it can be. Last week's top-off was not enough to reset my fuel indicator and looked like 3.3 gal. for 208 miles, 62 MPG. All weekend, I drove around with an indicated 60% full, according to the fuel gage. Then Sunday evening, I topped off and put in 3.4 gal for 108.0 miles, 32 MPG. Then I remembered the variable fuel tank.

What probably happened is the tank had a bubble large enough for about 1 gallon of gas in the first fill-up. So it didn't really fill up the tank which explains why the fuel gage never reset. Then when I filled up Sunday night, the 'bubble' was gone and an extra gallon went into the tank. When you add both tanks and miles together, 6.7 gal and 316 miles, the mileage comes in closer to the expected 50 MPG (I had used the AC on a couple of very hot trips.)

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Yep, check my tanks, too. You'll see the discrepancies between actual and MFD-calculated FE. Most of the time actual is lower, but the most recent one was higher! I'm also tracking when each of the pips disappear on each tank to see if there's a pattern. There's a LARGE variation there, as well.
Congrats on a great first tank!

Change what & how I drive, not who I am. Rack 'em up.

I have only had my Prius since early May, so I am still learning, but I have tried to minimize the tank variability by letting the pump shut itself off, then pulling the nozzel out to the end of the blatter and slowly adding fuel until it is totally full. It seems to be pretty consistent so far doing that, Just got 644 miles on my last tank, 10.5 gal, 61MPG. Hope you just keep getting better tanks every time! Congrats

Congrats on the superb results of your two months practice with your Prius! .. 61 MPG is wonderful!!

Cheers!

My first tank of my new Prius the other day was 30.378 mpg. Now granted the fancy screen said 40.1 but, supposedly, the dealer filled the tank up. I put in 9.372 gallons into the thing and had 284.7 miles on the odometer.

Did I set a record low?

I will figure maybe the dealer really didn't fill it. The gauge looked like it was reading full, but who knows. I am still trying to figure this thing out.

Bill
Mount Pleasant, SC

Hi Bill,

OWCH! That is not good. Even for the variable size tank, due to the bladder, that is way off. But don't feel bad. My first tank was 39 MPG and I briefly thought about turning around and taking it back:

http://hiwaay.net/~bzwilson/prius/

Scroll down to see my MPG vs miles per hour chart.

Let's start with the FAQ maintenance:
1) tire pressure? (should be 42 psi front and 40 psi back, dealers make them 32 psi)
2) oil level (is it above the "F" mark)?
3) cycle the parking brake?

Operating speeds and such:
What sort of driving were you doing? (City, highway, mixed?)
Headwinds?
Were you able to avoid 39-50 miles per hour and stay at or under 65 miles per hour?
Were you using the AC on AUTO or MAX?
Are you able to do about 1-2 miles at neighborhood speeds, ~25 miles per hour, for the first trip of the day? Once the first warm-up is done, you're good to go.
Can you 'coast-in' at the end at speeds of 30-35 miles per hour to maximize electric vehicle (EV) mode?

The gage is notorious inaccurate and worse, the bladder makes the tank 'variable' size. Some of my data suggests the difference can be as much as 1 gal. The bladder tank has a system for capturing the gas fumes that goes beyond the ordinary cannister capture system.

Let me suggest to review the FAQ and feel free to ask questions and/or add any observations. I'm always interested in making it better.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

I had the same thing when I filled up with my first tank this weekend, but I think I beat you. 255 miles, 8.479 gallons, for a whopping 30.1mpg. Brand new 2006 Prius, and like you the fuel gauge looked topped off when I picked it up. I think they might have been idling the car for a while prepping it before I picked up, as my MFD said 16.7 mpg for the 8 mile drive home from the dealership (even though from the current mpg display, it looked like I was hitting 50-60mpg on most of the way home. I also had tint put on last week, and my display mpg tanked when I picked it up so I'm guessing they were also idling the car while installing the tint.

Anyway, chalking the first tank up to those two items and maybe the bladder not being expanded as much when they filled it. Does the MFD show the lifetime average mpg, only trip mpg, or both? When I had the lousy mpg from the dealership to home, I reset it the next morning to see my mpg for my daily commute (55.6 mpg, by the way), but I'm scared that I can't get the MFD lifetime reading anymore since I did that reset.