That Darn Gas Gauge Again

I, too, have the inconsistent bladder. However, I'm truly getting over 50 mpg on each tank (now that warm weather is here). Also, at my age, there's another type of inconsistent bladder problem!

 

Debugging hardware & software problems is what I do professionally, as a programmer. And I've been doing it for over 20 years now. So as you could imagine, nothing surprises me anymore.

When a fix is proposed, I beat the crap out of the idea before committing to it. Most of the time, that means we end up discovering a shortcoming and end up back at the drawing board.

That's why I want the solution to be BULLET-PROOF before taking that next step.

There's nothing worse than investing a ton of resources on a fix only to discover you hadn't taken some abscure fact into account... in other words, finding out the fix won't help everyone.

The lack of consistancy among the reports we have is a clue that we haven't taken everything into account yet. So I keep pushing with hopes of it surfacing, that someone will finally notice that "missing link". Once that happens, we'll be able to reproduce the problem every time... a guarantee that will prove the fix works. For all we know, it could be an external factor causing the problem, like a particular kind/age of pump nozzle sensor triggering at the wrong time. Who knows. Maybe its something really uncontrollable, like barometric pressure in combination with dew-point or humidity.

Anywho, the point is that I want the adjustment (whatever it may be) to work perfectly for everyone. Forcing someone to come in for a repair and it not working for them won't help anyone.

 

I'm not "claiming" 50+ mpg, I've got the records to back it up.

Perhaps your driving style needs to change to a more conservative driving style, as is much of ours.

Driving this car like a regular car, you'll get better than standard car mpgs. Driving this car like you're supposed to drive any car, you'll get 45-55mpg.

-m.

 

Time after time my gauge has worked perfectly. And sure enough, it did today too... triggering the "Add Fuel" message darn close to the 9 gallon mark.

Why?

It was really starting to bother me that some were having trouble, but not me. Why?

Then it hit me.

Toyota designed Prius to be the cleanest possible high volume car on the road, without conforming to limitations of today. They planned for the realistic future. So naturally, they would want to design for the cleanest fuel that will be realistically available. That realistic cleanest fuel is LOW-SULFUR E10.

There is a very high probability that LOW-SULFUR E10 does not have the same density as the dirty non-ethanol mix gas many of you are still using. That reveals a very clear difference, because my Prius is using LOW-SULFUR E10.

A different type of gas could cause internal sensors to work differently.

Does anyone know how my LOW-SULFUR E10 (that's 10% ethanol, 90% gasoline, with sulfur content averaging 46ppm) compares on the "liquid quality" scale compared to normal 100% high-sulfur gasoline?

 

I don't know. My issue hasn't been as much with when it's time to fill, just with how differently the guage acts on every single tank. I typically fill up at the same Conoco station every time I refuel the car.

 

An interesting thought. According toThe American Coalition for Ethanol ( http://www.ethanol.org), ethanol has a molecular weight of about 48 grams/mole, while conventional gas has a molecular weight of about 100 grams/mole. So a 10% ethanol mixture would have a molecular weight of about 95 grams/mole or about 5% less than conventional gasoline. There may be other effects other than simple density, but that's not that big a difference - at least not as big as the variances reported in the gas gauge performance. In addition, I also use E10, and unfortunately, have not had the reliability you have had with the gauge.

 

The other day I was very happy to be averaging 53mpg and hoping that I might be able to hit 450 miles on the tank. My friends and I went hiking and parked the car at the bottom of the mountain with 3 bars on the tank. A couple hours later we came back and not only had it dropped down to one bar, it was a blinking one bar!!! I got gas the next morning and it upset me so much people at work noticed and asked what was wrong. I love the car but that's just ridiculous! I doubt someone siphoned off my gas.

Oh, the cap on the whole thing is that I could only squeeze in 6 gallons on the fillup. The most I've ever been able to cram in on an "empty" tank is 8 gallons.

 

> A couple hours later we came back and not only had it dropped down to one bar, it was a blinking one bar!!!

The real issue is that not everyone experiences that. For some, the gauge works perfectly.

That's why I keep digging with hopes of finally figuring out why.

So we now have theories about the bladder itself and the fuel you use, along with questions about whether or not you could cure the problem (reset a sensor) by completely ignoring once and driving to low (not empty).

 

My bad...I didn't intend to deny anyone's personal experience. Sheesh, I fell into the same trap that I accused others of!

I'm wondering now though if the bladder/gauge issue might be related somewhat to the differing mpg results? If you can't rely on how much gas was in the tank to begin with and the capacity seems to vary then how can you rely on mpg calculations? Also, how close is the MFD mpg reading to your calculated mpg? After the first 2-3 fillups my calculated mpg was so close to the display that I haven't bothered to keep up with the calculated mpg.

While I concede the possibility that my driving style may be partly to blame for sub 50 mpg (though I doubt it since most of my commuting days break 50) I suspect that terrain and traffic volumes are a more prominent factor -- but that's a topic for a different thread.

 

No problem, just wanted to be sure you know it's possible and has been achieved, and I know it can be frustrating to not be getting higher mileage (I will always be behind Evan, damn him and his ability to drive better! ). As far as calculated MPG vs. displayed - I'm still convinced one cannot accurately calculate how much fuel was used, especially compaired to the computer. Look - let's say you get the car with a "full tank" - except they filled it to 10 gallons, not 11.4. You run through 9 gallons, and are able to fill only 8 gallons into the tank. Even though you *used* 9 gallons, you tell yourself to calculate current miles divided by how much you were able to put in the tank. The only way for a 'simple calculation' of MPG to be constantly correct is to completely drain the tank each and every time, and I think no one wants to go through that. Sorry for my aside rant here, but I thought I'd bring it up once more.

-m.

 

We went on a little trip last week, to the Georgia Mountains, using "cross" country roads. A few Highways segments of 65 M/H where in it too, but no Interstate driving. We put gas in the car the day before we left to go home, it had driven 596 Mls, and alowed us to only put 10.5 gallens in it with no top off (57 F). The display showed 52.9 MPG. Now after we got back and I commuted back and forth to work for several days (40 mls/day), I had to get a 3rd fillup. It was in the 60s that morning, and I had put 588 mls on this tank of gas. The display showed 56.2, and the pump first stopped at 9.16 Gal. I top off this time and was only able to get 10.003 gal in total. It apears to me that the computer is off either direction, even though I put 10 gals in it I got calculated 58.8 MPG, which in it self is incredible, and the computer missed some gallens some where, and only registered 56.2.

Just thought I share that with you guys, lots of fun driving in to our green future,

Ralph
Check out my WEb-Site for some Prius Display picuters at http://www.ralphshotrains.com/Prius/ulthm.htm

 

That sounds so much like what happened to me (see my post on page two of this thread).

FYI, I drove from Phoenix to LA head on for hours in a colossal dust storm last night - 38mpg was all I could get out of my poor car. I had to fill up in Palm Springs. I've made the trip several times in the last month and NEVER had to fill up on the trip (one way). One time I actually got 450 miles out of a tank. I've not been able to repeat that feat since then, unfortunately.

 

last bar started blinking at 353miles :roll: i drove 10 miles to gas up, filled up 8.3gallons :?

 

It's really hard to find out what measures the fuel level in the '04 Prius. It looks like it may be a regular float type gauge. The test of the unit is to measure resistances from the sender and compare it to a chart. If the sender doesn't pass----guess what----replace the tank! Hope the sender never goes bad. On the classic (where this doesn't seem to be as much of a problem) there was a very complex fuel sending system that even included inclinometers to measure vehicle angle for assuring accurate readings on the gauge. You could access and calibrate the system through readouts on the IP. Looks like all of that got lost in the new Prius.

 

This is my newest experience with the car and tank.

Just for informational purposes, I've kind of given up.

Last tank - I filled at 30 miles past the blinking light, 270 miles, 47 MPG. Got 6 gallons in the tank. 100 degrees - car was warmed up.

This time I filled at 60 miles past the blinking light, 280 miles, 47 MPG. Got 8.5 gallons in the tank. 85 degrees - car was only slightly warmed up.

All I know is that I got more in (I didn't force it). The only thing different was that I was in Orange County (not LA). I've never gotten this much in the car before - it was obviously more gas than I used in the previous tank which leads me to believe that I have a bladder problem, not a gauge issue.

 

This tale touches on several topics covered in this and other threads, but this seem the best general topic.
At last fill I achieved 8.4 gals (usually 8.5. to 9.5 at 10-20mi past blinking bar, avg 460 mi, 52 mpg computer). The last .5 gal took about a minute. I manually reset the consumption screen, as it does not always do so on its own. Usually, the blinking bar attracts my attention as I am curious as to tank range. At night I turn the screen off. This time when when I finally noticed the blinking bar, I re-lit the consumption screen: 52.4mpg, 524 mi. and still > ten miles from the nearest gas, which was at home. Considering the 1.5x mpg blinking bar reserve, it was a somewhat tense, feather-footing, stealth, etc. drive home. The next morning I put a measured .5 gal in, car system off. In ACC mode this neither reset the blinking bar, nor the consumption screen. Not needing to go anywhere until running late for a dinner party that night I did not get to a station. In a rush that night, a quick calculation of impatient wife, gas station or remainder of home gas. With car systems running (I know, I know), I splashed in an unspecified amount, ca. 2 gal. When I got in there were three solid bars and the consumption screen never reset after round trip of thirty mi. I thought that if the consumption screen did automaticly reset it would do so when the ICE kicked in.

The main points being 8.4 gals, 52.3 mpg, 535 mi (when I finally reached home) and gauge ambiguity.

From the eastern Ozarks, Jay Shinkle at Iron Mountain, MO
traded 220 Kmi Previa for 04 Prius March 3.

 

Date Gal. Miles MPG CumMPG Notes
Apr 4 9.00 369 41.00 41.00 Local
Apr 22 6.50 285 43.85 43.85 Highway
Apr 26 10.00 428 42.80 42.43 Highway
May 15 10.44 496 47.51 43.91 Local

Here is a record of my gas purchases since I have owned my Prius. The second fillup which took only 6.5 gals was done to fill my tank before I got on the highway, not because my gas gage showed a low tank level. I have let the gage get down to one bar but never to blinking. The tank fills at a good flow rate and I never top it off. So please put me in the column for those who have not had a problem.

 

The Owner's Manual clearly says if you add only a minor amount of gas, it may not register on the gauge. In other words, you could cause that ambiguity.

 

Finally got past 500 miles on the tank yesterday. One bar had been showing for over 100 miles, but never blinked once. Crammed in 10.66 gallons, so the displayed 47.4MPG and the calculated 47.27MPG are close enough to stop calculating as long as I always cram.

However, the last tank had the gauge going from two bars to a blinking single bar just driving out to the road, so I can't say my gauge isn't flakey when it wants to be...