[ KB ] "Empty" fuel warning: results of an experiment

I believe I have a theory about how much fuel is left in the tank when the last bar flashes. I have (several times) driven from 30 to 50 or 60 miles past the blinking bar when I've been doing my standard around town/freeway/errands driving, and I have been able to put as much as 10.356 gallons in. I also got a second beep warning one time, and I filled up soon after that.

HOWEVER, on my recent trip to SF, where I was driving lots of miles without stopping, I got "the beep" at a bit under 500 miles (my display showed around 50 mpg) on Sunday night when I was not too far from my hotel, and within a few miles I reset my B odometer to make sure I didn't cut it too close. The weather, BTW was probably in the 50's at that time of night. I figured I had about 100 miles before I HAD to get gas, and that would put be at about San Jose (on my return trip) with plenty of room to spare.

On Monday afternoon, when I was heading south on I-280 (rural, with long stretches of rolling hills), I got the dreaded "out of gas" dash lights--and my odometer was at only 61 miles!!!! Plus, I NEVER GOT THE SECOND BEEP!!! I was on the downhill side of a hill, and I was able to keep my speed under 40 (in the emergency lane, which was blessedly clear) for several more miles until I got to an exit that I prayed had gas. I ended up having to drive over a mile at that exit, so I put more than 4 miles on the car after running out of gas, and my battery had 7 green bars!!!! I guess I had about the best out-of-gas experience possible, and I don't intend to do it again! BTW I filled it up with 10.361 gallons (I never top off) and my display was 50.0 mpg before I ran out.

NOW TO MY THEORY: I think that there might be something about doing big stretches of highway driving without stopping that fools the sensor. Since this is the first time I've set the B odometer to check the number of miles I got, I can't say for sure how far I've gone before after the bar flashes, but I certainly expected to get more than 60 miles after the warning. Also, since I didn't get the second beep, I think that my long-distance driving might have allowed the tank to drain more before the initial beep, and since I stopped for the night soon after that, the senson might have had time to "reset" to the lower fuel level, and I might have been past the "second beep" level when I started out that morning.

In any case, I am going to subscribe to the theory that I can have as little as 1 gallon left in my tank when I get the first beep. I don't want to run out of gas on purpose doing my regular local driving to actually TEST the theory (i.e. how many miles I have with local driving), but I thought I'd offer it for what it's worth.

BTW the very first time I filled up, I got 10.107 gallons in the tank, and I had gone about 35 miles past the first beep. I've always been able to get "around" 500 miles/ten gallons per fill, so I don't think the bladder is the issue.

 

Fuel Guage

I have never driven past the point where I only had one bar showing.
Exactly what is the sequence of what happens next, after the last bar starts flashing?

 

George, the display gets down to 1 bar, and at some point after that (30, 40 miles???) the bar starts flashing and you hear a beep. The screen shows a message at the top (add fuel). What happened to me in local driving was that after some time (another 40 miles??), I got another beep, or maybe it was 2 beeps, and again the "add fuel" message on the screen. I filled up not long after that.

When I was on my long-distance trip, I got the initial beep when the bar started flashing, but I NEVER got the second beep and I eventually ran out of gas at about 61 miles after the beep.

Moral--I will DEFINITELY pay attention to the beep on long road trips!!

 

I don't remember ever hearing a beep or seeing an "Add Fuel" message on the screen, though I might not have noticed the screen. I have driven maybe 5 or 10 miles past when the last bar started flashing.

After reading stories like those posted here (and BTW, thanks to all who have shared such stories, and especially to those who have run out of fuel on purpose in order to help us all) I adopt the conservative approach:

I fill up at the first convenient opportunity after the display goes to one bar, or at the first opportunity, convenient or not, after it starts to blink. I sometimes fill up when 2 bars are still showing if I have time on my hands. Sure, I only get 6 gallons in then, but those 6 gallons last me 3 weeks!

The variability that ericst documents in his own car, and the variability that others have reported between cars, leads me to the conservative conclusion that when the last bar starts to blink it's a good idea to add gas.

 

with my car i've come to a consistent indicator of how much more i have in tank. i've been filling-up when it reaches 400 miles on a tank, blinking or not blinking, and everytime i'd fill it with about 9 gallons. this has been consistent with my car. so when i reach 400 miles i figure that i have 1.5-2 gallons left, no worries. :wink:

 

Living in the UK, I don't have a bladder. Not in the fuel tank, anyway. My fuel gauge is absolutely consistent and reliable, the last bar starts flashing at 8litres [c2gal] remaining, and filling up is consistent and confirms this figure. In the UK and on Prius-Europe Group, no problems of this kind have ever been reported.

It seems virtually beyond doubt to me that the inconsistencies in the US version are caused by the insertion, through a design change, of the expandable fuel bladder in the tank.

regards

Jerry
UK

 

Jerry!!!!! So very nice to see you here on Priuschat!! I think a number of people have migrated over here from the various Yahoo groups because of the better layout and thread management. Either that or enough people have their cars now that there are fewer "discoveries" and more idle chat or bickering. Whatever the reason, I seem to be skipping over a lot more posts than I used to! I certainly have missed your entertaining and informative posts on the 2G group, and of course Wayne's departure was sorely felt too.

I know many people complain and moan about the "guess" gauge, but there's no problem as long as you don't try to wring the last drop out of a tank of gas. I'd much rather have the benefit of reduced emissions from tens of thousands of Prius than a gauge that is absolutely 100% accurate. I can usually get about 500 miles out of a tank (warm, sunny San Diego), but if I get less--so what? I just pay closer attention to the blinking bar since I ran out of gas that one time!

 

Danny: Thanks for sharing the results of your experiment. I add fuel within 30 miles of the moment the last bar starts blinking, and the tank invariably fills with 9 gallons. When the bar starts bllinking I too have about a quarter of a tank left.

 

How much gas remains when the last bar starts flashing can be considerably different for different cars and even for the same car under different circumstances, at least in the US "bladdered" model. Two weeks back I ran out of gas after a mere 10 miles after the last bar started flashing. Since then I have been filling up as soon as I am down to one bar, at the latest.

Jishnu.

 

Re: [ KB ]

Warning relating to running the fuel low or empty in any late model vehicle. Back in the "good ole days" you could run a vehicle out of gas and refill without any problem. Low pressure fuel pumps were mounted on the side of the engine block. The fuel pump was mechanical and ran by an eccentric off the vehicle camshaft. With higher pressure, closed loop modern fuel injected engines its a different scene. The majority, if not all, late model vehicles have electric fuel pumps that are located within the fuel tank and are cooled by the fuel they are bathed in. It states in the Prius manual and its good practice in all vehicles to maintain at least 1/4 tank of fuel at all times (pg114). What they dont say is it keeps the fuel pump temperature down and the pump lasts longer.
As a fleet mechanic I have experienced many a pump failure shortly after having an operator run it out of fuel. Coincidence?

 

Re: [ KB ]

Absolutely!

The fuel in the tank not only cools the in-tank pump, it also *lubricates* the pump. Run the pump dry and you dramatically shorten its life.

I also like to pick and choose where I refuel to avoid bad/unknown areas, so I like to top off before 1/2 if possible. And I always pick a fuel place with consistent, known quality.

 

"Empty Fuel" warning

amjimc (17 Mar) Many thanks for your explanation of one (the?) reason for fueling before dry tank. The owner's manual should give more than the general disaster warning.

I get so peeved with :guns: M.D's who, similarly, just say "Do" or "Don't," assuming that we are too stupid to help with our own health practices; or if we are so dumb as to choose contrary to their "orders" we deserve the unnamed consequences.

I bought the $300 set of maintenance manuals, but haven't learned how (quickly) to find what I need, and the service technicians at my Toyota shop give answers to my technical questions that sometimes amount to an assumption that Toyota wants to keep much technical data as trade secrets.

I discovered this site only last week , after nearly a year as a happy 04 Prius owner, and hope to learn, and eventually contribute to the knowledge base. :mrgreen:

 

Actually, the manuals are written in such a way that as little engineering information as possible. Often New Car Features gives more info than the repair manuals.

 

Got the warning and the beep, just filled up today after the bar started blinking. 10.526 gallons. My gauge seems heavily weighted toward the high end -- I can go close to 100 miles before the right bar drops, but I get the feeling that there ain't much left with only one bar showing. That's good advice to keep gas in the tank to lubricate/cool the pump.

 

Re: [ KB ]

I don't recall hearing nor experiencing a 2nd beep after the first beep for "Add Fuel". Does it happen in the same driving trip?

Meantime, I got my recent beep at 490 mi, stopped for gas at 530.6 mi and filled 12.001 gallons with the MFD @ 45.8mpg. First click was at 11.3 gal.

I try to never drive it past 50-60 miles after the first beep if I can help it.

 

I only get one beep per trip.

 

I've heard the beep and seen the message, but only once per trip. However, I've never got anywhere near 10 gallons in. On average, I only get about 8 gallons in. The most was 9-something. Is my tank on the small side, or is the flashing bar coming on early?