Fuel Gauge Issue

So please remind me of the issue mentioned in the title. The most gas I've ever put in my 2009 Gen II is just over 9 gallons, 450+ miles (middle of August 2015) - I usually fill up at around 300 miles on the trip odometer, the gauge at just under ½ way, it is a VERY BAD IDEA to run out of gas, and there is absolutely no reason to let that happen since there are so many gas stations and at just over $2/gallon, no earthly reason to run out. It can be quite expensive to let the tank run dry. In many modern cars including the Prius, the fuel-pump is immersed in the tank to keep it cool, and can suffer overheating and damage if the tank runs dry! Run out at your peril! There's no excuse, unless your fuel gauge is not working! There's a reason why the last "pip" on the gauge flashes, it's warning you that you really …NEED TO GET GAS! …NOW!!!! - hope this helps - Wil

 

I believe as soon as you hit one bar, that bar starts flashing, and it's also the same time your Cruising Range hits "0". You can go probably another 50 miles, but I've already started looking for a favorite gas station by then.

 

The main "issue" is just a compulsion to run the tank near-dry. There is zero upside to this game.

 

i think you are doing the right thing, asking here for advice. cause for concern? possibly. worry? absolutely not. 25 miles is not a big variance, nothing is exact in the prius fuel system. but only going 4 miles on the last bar is cause for concern.
i think the best thing to do is run another tank and see how she does. if the same, or a similar thing happens, you may want to start be recalibrating the fuel gauge. all the best!

 

That's well under a 10% difference, which is nothing. You can get a greater variation on that just due to the weather (cold temperatures, rain, etc.). Don't worry about the difference. And don't tempt fate by making a habit of running the gas so low that that last bar flashes - there's almost no upside and a lot of potential downside. One trip to the dealer to reset the error codes that running out of gas might get you is far more hassle than even a couple of extra trips to the gas station every year is worth.

 

Following that logic, I've got pretty much half the tank that's just along for the ride: I fill up anytime the gas gauge is below half. Arguably, that's about every 3~4 weeks, so still not a frequent chore.

I've found there can be things that bug the cr@p out of you, and then 20 years later, you wonder what all the fuss was about.

 

That strikes me as saying that insurance is not too useful since you hardly ever use it. There are things in life that you have "just in case", and that extra gallon is one of them. You've gotta ask yourself where you draw the line? If hauling around an extra gallon is too much, how about hauling around extra quart quart? A cup? An ounce? The less "extra" you haul around, the greater the risk that you've cut things too close.

Without any extra, then you'd almost certainly have already run out of gas once or twice, and the convenience of avoiding that kind of inconvenience makes it well worth it to haul around an extra gallon, IMHO.

 

A car with a needle gauge, you'ld never have this "issue". How to fix: fill up when you've got a couple of bars still showing.

 

I've seen my fuel gauge do the same thing; but I never get so low as to see it blink. It seems to be related to uphill downhill attitude of the car and position of the fuel level sensor.

 

If the gauge isn't located in the exact centre of the tank then its reading can vary when you drive between level ground and a grade (i.e., going up or down a hill) because the fuel will moves from one end of the tank to the other in accordance with the law of gravity.

With analogue fuel gauges many of the cars I've driven tend to indicate there's a bit less fuel in the tank when going uphill. That kind of effect is harder to see in the Prius C because the fuel gauge has a much coarser indication, but if your fuel level is right near the boundary between, say, one and two bars then it sure wouldn't surprise me to see that happening.

 

Hey Gabriel you may want to like the two posts above since they get to the heart of the fluctuations. I've seen my fuel gauge on different occasions fluctuate both -1 and +1 tick just because the fuel level sensor says it's right in between. That would also explain why it may take a few extra miles to get the last bar to flash. So, nothing to worry about there. I think that your sensor is working as intended. On another note, I've noticed that the first tick goes from 9.50 to about 7.90 gallons; the scale is not linear.

 

Based on my experience with various cars over several decades, I think you are trying to extract more detailed and precise information from the gauge than it was intended to provide. Most fuel gauges are just cheap indicators, optimized for low manufacturing cost. They also contain significant 'customer expectation management' biases, e.g. margin at the bottom so customers cannot legitimately blame the car maker when they run out of fuel.

The top of the gauge is not at the real top of the tank, the bottom of the gauge is not at at real bottom of the tank, the gauge subdivision markings are not at equally sized fuel increments, the gauge does not perfectly filter out the fluid 'slosh' from hills and corners and speed changes, and it doesn't read the same every time. Though my Prius fuel gauges haven't been nearly as bad as the analog gauges on some of my past cars.

That 'extra', or 'insurance', was less than zero on the very first car I actually owned. It ran dry with the fuel needle still above E. It isn't real insurance if you merely take it on faith that the fuel might be there, when experience already includes events where it was absent.

A later car had close to 30% of its claimed tank capacity below E, more than 4 gallons. Using the same safe lower limit gauge rule needed on the first car meant very premature refueling stops on one of my regular trip routes, in the severely overpriced fuel zone.

In previous threads, I've better explained my methods and personal reasons for testing the lower levels of the fuel gauge on new-to-me cars. I don't expect understanding or agreement from drivers too young to remember the OPEC Oil Embargo, or who live in regions with no meaningful price competition (e.g. British Columbia), or who don't drive in areas with signs such as these:

DSCN1334gas106c.jpg by fuzzy1 posted Mar 22, 2014 at 10:15 AM

gas163mi2.jpg by fuzzy1 posted Mar 13, 2014 at 9:27 PM

gas150km.jpg by fuzzy1 posted Oct 14, 2012 at 7:01 PM