what the #$$%^ my MPG ....

There is a reason that we call the Gas Gauge the "Guess Gauge". First, because the tank has a bladder (search forum for more info) the capacity of the tank is less than 12 gallons. Normally, after the add fuel warning comes on, I only get 8 gallons before the pump clicks off. When it is cold outside, you have less capacity. Secondly, the gauge is not linear. You cant use it to tell how many miles you can go. Once you get a few tanks under your belt, you will get a better feel for it. When the last bar on the gauge starts flashing, stop for gas.

As for your assumption, no, you won't be able to go 600 miles if you get 50 MPG. More like 400 miles.

 

The bladder tank's effective capacity from full to flashing pip is ~8-10 gallons for most of us. (9.95 gallons is my max so far, some get more, some less.) The flashing pip is ~1/8th tank, similar to the E line of analog gauges of other Japanese vehicles I've owned. The bladder however makes the reserve capacity variable (just like the fill volume) so the flashing pip means get gas ASAP.

 

I usually can only get between 8-9 gallons when I fill up (always when down to the last pip, sometimes after it is flashing). Depending on your trips you may be getting closer to 40 than 50, possibly under 40 when temps drop and if trips are short (I get closer to 30 in the dead of winter with short trips). I rarely can make 400 miles on a tank. Usually between 350-375 is normal for me.

 

Hello Happy:

I see that you're new here. Spend some time searching the threads on the G2 gas tank issues cause by a combination of the "bladder" used in the tank, as well as the way that the "guess gauge" works.

A well documented issue. Nothing to be alarmed about, although it can be annoying.

 

I tend to refill my tank by mileage rather than by the gauge, at 400 miles, I am in the mood to stop and stretch anyways. Once the last pip starts blinking you are in desperation mode, I have gone as many as 30 miles, but run dry in as few as 7 miles. I always try to get gas BEFORE it blinks.

At the other end of the tank, I go from 100 miles to 160 miles before the first pip disappears, so it is not accurate when full either. I plan my fill ups at 400 miles, I find it less stressful. (I have not been in a winter yet, and may need to re-assess my distance once I know my winter mileage. Of perhaps not, winters seem mild here 42 MPG average so far)

 

You may need to recalibrate the AZ/EL sensors. They affet the gauge readout accuracy

 

There is nothing really unusual about the top of the tank being above the top pip indicator--certainly no reason to suspect the sensor calibration. That's normal in every other vehicle I've had. It represents the portion above the Full mark and is usually about 1/8th tank in my experience.

The difference with the bladder is that the top and bottom levels are highly variable. It's nothing unusual to have have the fill vary by 10% or more in back to back fills with similar conditions. Previous tank I did at 52 mpg took 10 gallons (new record fill), this one took just shy of 9 gallons at 50 mpg...despite being 18 miles more.

When you have a problem is when your tank goes empty before the flashing pip. The flashing pip should be about 1/8th tank indicated (to dead empty). That is the norm in other vehicles. Obviously something isn't right if the tank goes empty before the flashing pip.

 

Umm... I only get 45 MPG and I've gone 480 miles easy.

 

I get 200 miles on my first gas blip

 

I've got 157 miles so far out of the first pip on this tank, and it was about a gallon short of expected based on indicated mpg. (Calculated mpg was 10% higher than indicated.) So I'm wondering when the first pip will fall.

Sure wish Toyota had put in a useful gas guage. According to Scangauge owners the increment is actually 2.5% IIRC. But instead Toyota gives us an indication with 1/4th as much precision. Just f****** brilliant that move was. Thanks for treating us like 'shrooms, Toyota. There are two gauges that owners check regularly: the speedo and the fuel gauge. Toyota only managed to get one of the two right. How friggin' hard is that?

 

http://priuschat.com/forums/gen-ii-...tila-vass-s-visit-w-chief-prius-engineer.html referenced the bladder and "guess gauge". I wonder how accurate the 2.5% increment is. After all, they're reporting some value but for all we know, it could be off +/-10.

I was a a hybrid seminar at Toyota Sunnyvale in 06 given by a very knowledgeable rep and he pointed out the the area in the tank/bladder where they have to take samples (to get level readings) is unfortunately very small. He said something to the effect of that he'd hate to be the engineer who had to design something to produce values based on the tiny area.

 

The absolute value (accuracy) of the increments is not my primary concern...as long as it isn't running out at the flashing pip (12.5%). If we could see progression to the tank level (those 2.5% increments) we would have much better information with which to make decisions. Instead we've got a tank that will go 160 miles without any indication of level change. With an analog gauge you would see the needle moving even above F.

Yes, the bladder introduced many unnecessary compromises and variability, but that was compounded by the choice of the gauge interface.

 

Sounds like Happy is only getting about 40 mpg. Which brings me to my own question. My energy screen shows that I'm getting an average of high 40's and low 50's mpg, but if I calculate my mileage the old fashioned way I'm only getting low 40's. That means the energy screen is lying to the tune of 10mpg+.

I've got an '07 with 27.5k miles on it. Bought the thing used and am just learning about these vehicles. I live on the west coast of Florida. Lots of flat driving and always warm weather. Lots of gliding and lots of driving on battery at 35mph. My commute to work is 8 miles and I can glide or use battery for at least 25% of the run (the screen shows high 60's for those sections). Why don't I get better mileage? And if you're wondering why I don't just ride my bicycle, you haven't driven the roads around here. It's murder...for real.

 

Doubtful. I've not had any trouble with the energy screen misrepresenting. However, I also factor in distance covered during the 5 minute increments...

Are you recording the indicated MPG for each tank? That's how you can tell if there is a discrepancy between the MFD and the actual fuel from the fill.

 

No there wasn't enough information to make any definite statement about Happy's mileage. He thought he had used more fuel than expected, base on the MFD's MPG readout, but in reality we have no idea exactly how full his tank was to start with! So basically there is no reliable data to make any conclusion there.

How are you doing your "old fashion way" measurements Richard? You know about the fuel bladder and the resulting inconsistent fill volume right. This means that you can get very inaccurate results doing the manual MPG calculation over just one tank full. Let us know what the results are after you've averaged over three or more tank fulls. The MFD's results of high 40's to Low 50's sounds about right to me - I mean it sounds consistent with what others are getting.

BTW. If you really are getting a big discrepancy then one other thing you might want to test is the accuracy of the odometer. Say compare it with another car to make sure it's not under reading.

There's one thing about the all electric mode on flats that I've noticed Richard. It makes you feel like you're saving lots of fuel seeing it running all electric but in practice it can be less fuel efficient overall (not always but in some situation ok). Basically if after that all electric run the ICE is going to kick in and recharge it then overall it's a disadvantage to try too hard to keep it running all electric. Yes it's really good to use the combination of glide/electric/regen on down hills and keep the ICE off and the fuel usage at zero, but don't try to make it run too much like that on the flats unless you think you can keep it up until the next downhill section and regen the battery back up to charge for free.

BTW. Yours sounds real similar to my situation Richard (I'm also a keen cyclist - though not really fit enough to do it as well as I used to ). I also just got my Prius S/H and am still figuring stuff out.