I just gotta say I don't understand all this confusion about the guage.

First, gas guages are notoriously inaccurate - no matter what car you are in. The common implimentation is a float on a rod that waddles around in a somewhat isolated pool of fluid that moves around a little as the car moves. We can't call this in any way "accurate".

Second - how far you go when your light starts blinking is IN NO WAY relative to how much fuel you put in your tank originally - assuming, of course, that you at least started with enough fuel to not have the light blinking in the first place. It is relative ONLY to the fuel remaining and the efficency of the use of that fuel.

Third - no matter WHAT your average reading displays for the average consumption when blinking starts, the rate of fuel consumption (and the miles you may travel) once the light starts blinking is ONLY dependant on the current conditions. If you have achieved a 50mpg average on the tank, you cannot guarantee this will continue for the remaining fuel in the tank - you can only say "that is my tank average - SO FAR". (It is reasonable to expect the average rate will continue, however)

If you have a 50mpg average and the light starts blinking with 2 gals remaining (seems more like 3+ really), and you suddenly experience conditions that get you actual instantaneous mileage to more like 30 mpg, then you are not going to go 100 miles on that 2 gallons - you will go (about) 60. Your average display will start to decrease as this happens, but will not indicate 30 at the end, due to the buffering that occurs thanks to the higher mileage before. It may end up at say, 42, at which point, if you feel you had 2 gallons remaing, you might say "Why could't I go 84 miles, instead of only 60?" - the answer is for those last 2 gallons, you were only getting 30 mpg - not 50. Or even 42. The value displayed is an average of the entire tank, not the last 2 gallons.

So - what to do?

The easiest thing I can think of is to reset the display when the flashing starts and at least get a running average of those last gallons. That will help - but ONLY if you have a good idea of how much fuel you have left.

What *I* do is carry an extra gallon in the back the first few times - and I actually run the car completely empty a few times - and use one of the trip ODOs to measure the run time when the blinking starts. I am in NO way worried about the fuel pump overheating - the physics involved when this is discussed as a failure mode is flawed.

What I have found (and this ONLY pertains to me because of the variances alluded to above) is that I have about 3 or so gallons left in the tank when the flashing starts. I do NOT measure this by way of what I put IN to the tank at the fillup, but in how far I go with a reasonable approximation of the MPG on the display.

I have actually considered waiting for the flashing to start, then find a way to pump all remaining fuel into a can and measuring it - but that is just me!

I think it is very valuable information to get an approximation of your mileage from the flash start - wherever it may be. I think flashing early is a bit annoying - but on a "normal" car, a warning with only 2 (3) gallons left means only 30-45 miles of travel. With us, it is a bit different. Flashing later is less desirable - to me. If the car waits until I have only 10-15 miles left in it - that is about a quart of gas left! I cannot reasonably expect the curent state-of-the-art in flating gas measurement to determine fluid level down that low!

Sorry for the long post, but this has been sitting waiting to come out for some time now!

Jack

 

Interesting point you brought up. The last 3 gallons of the tank may not last as long as one may think. However, the "flawed" part that we're all talking about is that the gauge begins blinking approximately 135 miles before any of us have to fill up. It's a nuisance to put up with a blinking meter for 100 miles.

 

All I can add is that my last three cars 2 Acuras and last a Subaru were just as inaccurate as the posts above describe.

Roger

 

I agree with your point and can only say it is the result of driving a wonderfully efficient car! It is, however, really annoying - and I think a nice addition might be a timer or sensor that re-reminded you of the fuel situation either some degtree of consumption or some runing time later.

In my particular case, if the fuel warning goes off (why is it such a quiet, single, non-opbtrusive beep, when Toyota feels it is so totally necessary to tell you loudly and continually that the car is in reverse??), I can continue my drive to or from work, return home, drive in and back the next day and probably completely forget to examine my guage and notice again that I am low on fuel. I am sufficiently silly to dis-remember almost immediately the initial warnings on start up!

Let's presume a car that now gets 100 mpg. A similar warning at a similar capacity on such a car would offer 200-300 additional miles of range - but a warning for only 30 miles of range would necessitate a system of detecting only the last 1/3 gallon in the tank! That is a very small amount for such a gross measuring system to accomodate.

Better systems add too much to the cost of the car and have their own issues. I am sure it will get beter - but for now, we just have to learn to work with it. Or carry a bit of spare fuel! (A DANGEROUS practice I do NOT condone - but do every time my light flashes!)

What would you think would be a reasonable, cost-effective method to resolve the low-fuel sense issue? I can think of a few things that might work, but I am not certain how effective they would be - and they certainly would be more expensive.


Jack

 

Here's one: fuel alert @ 1.5 gallons. 50-75 miles is adequate.

 

I guess this is in response to the question "what would you think is a reasonable, cost effective method...."?

I agree - this would be handy - even desireable. Heck, I frankly would like to see less - in this car, you could easily forget about the warning if only a gallon were alarmed. a 20 mile warning is just about perfect - but that is less than 1/2 gallon in this car.

Thing is - HOW to do this? With the float method used currently in most cars, measuring this little fuel is really a problem. It is not a problem in other cars, because you might only have 20 or 30 miles left with 2 gallons!

The only way I know of would be to make the sensor area - the pool of fuel where the float is placed - quite tiny. A vertical float would have to be used - most today are swing-arm type, but vertical displacement shouldn't be a big issue technically.

What I don't know is if shrinking the measurement area presents other problems such as sloshiness (the effect where the guage would change radically with radical movement of the car) or not.

The tech of this car has not been matched with inexpensive tech to measure a much smaller quantity of remaining fuel. That is all I am saying here. Guess one more patent in the car was just too much of a good thing!

but you know - I bet we see it happen inthe next year or two. I am really impressed with those engineers at Toyota. And they do seem to be listening.

Jack

 

I have had various results when filling up my tank. Twice I have filled up within 2 miles of the add fuel warning (blinking final bar) and twice about 30 miles after the blinking starts. I set the rate at the lowest setting and when the pump stops, I do not try to top off. The total gallons pumped seem to have a strong relationship to the ambient temperature:

- 7.692 gallons, Blinking for 30 miles, 12 degrees F
- 6.942 gallons, Blinking for 2 miles, 16 degrees F
- 8.130 gallons, Blinking for 3 miles, 28 degrees F
- 9.583 gallons, Blinking for 20 miles, 35 degrees F
- 10.144 gallons, Blinking for 22 miles, 56 degrees F
- 7.030 gallons, Two bars left, 42 degrees F

With some additional data, I may be able to plot something useful.

Dan

 

I got 47.0 MPG on my first tank. I filled up after about 40 miles of blinking and added 9.1 gallons after 350 miles. How many gallons does it hold?

 

The tank capacity is listed as 11.9 gallons. How much it holds seems to depend on alot of variables. Temperature seems to be one of them. If I were to guess, it was about 32 degrees outside when you filled up.

By the way, 9.1 gallons for 350 miles sounds like 38.5 MPG to me. Maybe I am reading your message wrong however.

Dan

 

Although my new white or light brown Prius #9 hasn't arrived yet, in spending about 12 hours on the 'Net researching the new Prius, I've read that the reason for the fuel guage inaccuracy is due to the expandable bladder in the fuel tank. The geniuses(!) at Toyota felt that the bladder would prevent evaporative emissions from the fuel tank. Unfortunately, the bladder isn't very flexible in cold weather and consequently doesn't completely expand when filled with fuel. Warmer weather should allow more accurate fuel level readings.

Fortunately, if we run out of gas in the Prius, we have the electric motor to continue to power the car.

Hmmm . . . Maybe if we lit a small fire under the fuel tank on cold winter mornings . . .