I know the fuel gauge isn't very accurate but...

The gauge is NOT linear. You can't extrapolate from how long it takes for one or two bars to extinguish.

Search on "gas gauge" and you will find some inadvertant pedestrians who thought differently.

 

Put gas in it! I can't believe how many people on here have run out of gas. You would think that, driving one of the most fuel efficient cars on the planet, the likelyhood would be LOWER for running out of gas. But, it seems everyone likes to stretch it, trying to get that magic 500 or 600 miles per tankful, completely ignoring every indication they are running on fumes. The car does not know how far you filled the gas tank last time, so extrapolating from the mileage you've gone seems worthless, yet people insist trying to do it.
Just my observation. I think its funny! :lol: I just hope I don't fall into the same trap once I actually OWN a Prius. :blink:

 

Yeah, but on the other hand *I* know how much gas I put into it. Say that I put exactly 10 gallons in my last fillup. As I approach 480-500 miles since the fillup, my MFD says I am average 51.5 MPG. Would it not make sense that I could expect to get somewhere around 515 miles from the gas I put in? and unless I am flooring the prius at green lights, I wouldn't expect the average to jump down a whole bunch. Based on my experiences with the MFD, it is fairly accurate.

 

I put in 29 to 31 gallons every 4 working days. I get 530 to 550 miles in that time. It costs anywhere from 90 to 100 bucks to fill it up.

I figure when my prius gets here, I'll save about $360 a month just in the difference in fuel cost for the amount of fuel saved.

Anyone in the Illinois area need a 4x4 diesel pickup?

I should be more energy efficient somewhere in late January last I heard. I have Package 5, green on the way.

 

Amen. I too, get tired of hearing this...if one had a 'regular' car, would one try to drive it to fumes as well? I know I would not. Just get gas. What is the big deal?

 

Have a look at my mileage chart (link in my signature). The MFD can vary 2-5 MPG in EITHER DIRECTION from what you are actually getting.

Running out of gass isn't fun. The worst I do is wait for the blink. It blinks - I get gas. Most people in "regular" cars won't let it ever fall below 1/4 tank, so why should we?

As an electrical engineer, I have to add that just because it's a digital gauge doesn't mean it's an accurate sensor. They probably use the same sensor as al the other cars they make. Also, there are a number of tricks being used so that it doesn't suddenly fall off if you go up a steep hill. Sure, I'd love more 500 mile tanks, but I would sure hate walking a few miles to get the extra 25 on the car.

 

I don't think Vespasian is talking about running on fumes. My MFD lifetime runs about 2% better than my actual gallons in / miles driven. (Sorry I haven't updated my sig lately). If we use that 2% on this example, the actual MPG would be about 55 and 6.7 gallons would have been used to go the 370 miles. Thus there should be at least 5 gallons, or 275 miles left in the tank. I would NOT believe that to be true, trust the gauge. Put gas in it no later than shortly after you get to 1 flashing bar. I expect that to be somewhere around 450 miles for you THIS time.

The car does NOT know how much you put in. My guess is that you didn't fill it up all the way, never an easy thing to do in a Prius with a bladder (none in Europe). Just because you are getting 55+ MPG doesn't mean you can drive 11.9 gallons * 55 before coasting into the gas station on fumes.

I haven't ever had a car with a linear gas gauge. My last vehicle was about 65% from full to half, then 35% to "add fuel". The Prius bounces all over. TONS of miles to 9 bars, then maybe 70% of my current tank mileage (from MFD) down to about 3 bars, then it seems pretty consistent with the MFD down to 1 bar.

 

Exactly, Vespasian never said he "put XX gallons into it" last time he got gas, so I assumed that either:
1) the station he filled up at kicked off early, due to the tight emissions seal around the nozzle, or the angle the car was at while filling, or the sensitivity of that gas nozzle, or
2) the bladder was cold/contracted when he filled up, not allowing as much fuel in as usual.
Vespasian, of course you can calculate the longterm gas mileage, people on here do it all the time with high accuracy. But, the STORAGE capability of the tank has NOTHING to do with the gas mileage. Miles per tankful, yes. But, due to the inconsistancies of the bladder and different gas station's pumps, you're best to fill up when the car tells you so.

 

Calculating avg for a SINGLE tank using gallons in / miles driven is NEVER accurate. There is no way with any vehicle to make sure it is filled EXACTLY the same each time. If you were to ALWAYS put in EXACTLY 8 gallons every time you filled, you would have an accurate avg (ignoring the 1st tank). Otherwise, I think it prudent to trust the MFD value to figure out how much gas you can get in. If yours, like mine, is a little generous, you can't put in more than the calculated gallons used. For REAL lifetime, keep track of miles and gallons, that is the TRUE average. It isn't accurate for the first few tanks but the more times you fill, the less the inaccuracy of the first and last tank will influence the overall average. At some point, they will have no statistical effect.

 

Nope, because you're not running it to empty every time. Still not exact. I ran out of gas with 1/2 tank in my Chrysler once. Gauge had broken. So if it's not "perfect" why do we expect it to be? Be safe - fill up with a reasonable amount still in the tank.

 

I don't think I've ever owned a car where the gas guage was linear.

On my old Ford Explorer, for instance, the fuel guage needle would get pegged well past the "F" on the guage when I filled up. It would stay pegged for a day or so or driving and then would start moving down. Around the half full mark, it would pick up speed.

My prius behaves the same way. It stays at 10 bars for about 150 miles, then starts dropping. Around half full, it picks up speed.

Has anyone had a car where the gas guage was linear? And unless you were tracking your miles closely, like we tend to do on the Prius, how would you know?

My guess is that gas guages are not linear because they only measure the gas level and gas tanks are usually not perfectly square. If the tank is tapered at all at the bottom, because of rounded edges or whatever, then the level of the gas in the tank is going drop faster once it gets to the point where the tank starts to taper.

 

I agree with Marlin. I've never seen a linear gauge, and I really don't understand why that's the case. Even an irregular shaped tank could be characterized so that a particular reading from the sensor could be fairly accurate. This is especially true with a digital system like the Prius uses.

BTW - Does it annoy anyone else that the Prius doesn't report "miles to empty"? My last two cars had this feature. On my '92 Saab it was even pretty accurate.

 

It would be nice if the gauge was at least consistent.

The tank before last - the first bar clicked off at around 200 miles. I got 580 miles on the tank.

The current tank - the first bar clicked off at 70 miles. Now at I've only got 200 miles at half the tank gauge mark.

It was really weird after the last fill-up too. After completing my fillup and turning on the car, I watched the fuel gauge bars slowly creep up from half full to full in about 20 seconds while I drove away.

Could it be the colder weather? Maybe it's the high humidity from our 8 days of continuous rain this past week.

 

The '94 Intrepid that my Prius replaced had a damn good fuel gauge. Probably about as close to linear as one could expect. It had the same problem as the Prius, where a completely full tank would register higher than the gauge's scale (and thus peg it), but as far as I could tell it was linear once the level was back in the supported sensor range.

On a long trip I calculated how many highway miles it took before the needle began to drop, then from there how many miles it took to move down each quarter of a tank. Turned out to be something around 96 miles per quarter. I could go about 420 miles on a full 18 gallon tank, so those "unaccounted" 36 miles were from the level above the sensor's maximum range.

The low fuel light would come on, according to the manual, when approximately 2 gallons remained and from all my fillups it was close enough for government work.

My late-'05 Prius' gauge also doesn't seem to fluctuate quite as much as people here report... maybe they've made some algorithm improvements in recent production?