Ran out of gas after 472 miles

Good point. I have never before owned any car that gives me as many warnings about a low fuel level than does my '05 Prius. If I choose not to take appropriate action after 3 separate warnings, only I am to blame.

 

Maybe I missed it, but is there some sort of contest to see how far you can get before running out of gas? Must be, since so many people seem to be trying to get maximum miles with minimum fillups.

Just fill the tank people! It's easy to do. There is no prize. There is no glory. No one is going to pat you on the back except yourself. Just fill the darn tank.

...oh and stop posting I ran out of gas threads.

 

I've had the pri for 8 months. Just the thought of an aux tank, a 70-gallon aux tank, blew me away, until I realized that in my previous vehicle (8-cyl jeep), that was about 3 weeks of gas.

 

I would rather go to gas stations just a bit more often than to go through these gyrations. BTW, do you do this when the station is busy and people are waiting? Have you ever been filling using the auto lok and the person next to you does the click-click-click-click-click and keeps shutting yours off? I HATE that!!!!!

 

I think you miss my point, quoted above. Of course you should seek a fill immediately if you get the warnings, but maybe it's too late because:

2) There is no way of knowing the volume in the tank and therefore the potential remaining range based on the tank mpg readout, at _any_ point in a journey after a fill-up.

3) The amount of gas remaining in the tank when the 3 warnings occur is unknown

4) Because of 1) and 2) you may be out of range of a gas station when you get the warnings. There are some parts of the US where gas stations are 50-100 miles apart, or more.

5) Toyota has been insufficiently specific in warning buyers of these uncertainties; these are persons who have been used to known-volume tanks where range could be estimated, and the gas guage callibrated, and so they are more vulerable to falling victim to the Prius bladder uncertainties.

So even if you heed the warnings, you may run out of gas.

The advice is often given that one should never let the gas fall below two bars: that is good advice, but one still does not know the remaining range - one could still be far out of reach of the next gas station in, say, Nevada.

I would not have stated it in quite those terms: I would say that Toyota failed to effectively assist the Prius owner to avoid the consequences of tank volume uncertainty, especially by not discussing the issue in the Drivers (Owner's) Guide, and instead hiding the variable tank capacity (incorrectly stated) deep in the manual, and failing to mention that the reserve capacity is variable.

By the way, I have not personally run out of gas (so I have no personal beef) and I have read much more on the issue than the average owner, so I hope never to run dry. But it will not be the Toyota instrumentation that saves me from that fate; it will be by filling much earlier that would be necessary if one had reliable instrumentation.

For a car (Prius) that has much greater potential range than my truck had, I am filling it more conservatively than the truck, because I cannot trust the Prius guage. I call that disappointing!

C

 

So, can I ask what you're doing that you need the full 11.900 gallons? For me, I drive by gas stations enough that it's not a problem if the gas tank holds 11.9, 9.9, 5.9, or even 1.9 gallons (OK. 1.9 could be really annoying). And, even if it only takes 8 gallons (a severe underestimate, but bear with me), the range is still greater than many, many other cars that that have 12 gallon tanks, or SUVs that have 20 gallon tanks. Was the 11.9 gallon tank a major selling point for you with this car? The size of the gas tank just seems like such a minor point in this day and age where there are gas stations on every corner.

I should say that I actually agree with the first point you made; I would like it if the "1 pip flashing" state started with a little more gas in the tank; this would make it more in line with other cars (i.e. my family's old Honda Accord that had a gas light come on at 2 gallons). And I also would like it if the gas gauge were more consistant (i.e. even if it's not a linear gas gauge, one pip should always be the same amount of gas from fill to fill, and it REALLY seems as if it isn't).

 

hmmm... you will most likely have just as much luck returning that mp3 player for shorter runs times than you would returning your Prius because it ran out of gas.

i have intimate knowledge of another product, cellphones, that advertises "run times"

i can tell you that you will also have no success whatsoever, returning a cellphone if you determine that the 180 mins of talk time are inflated. like a cellphone where failure to maintain the product may affect its performance, your Prius is also the same. you undertake a HUGE risk running it out of gas and lack of proper tank size as an excuse will never be accepted. get used to it. that is just the way it is

 

I don't think the issue is that the theoretical 11.9 gal capacity is so important. It is that the _actual capacity_ is variable and unknown. I'd be happy with 8 gals. if it were dependable. (However, If you are travelling expresssways in parts of the W US you DO need a good range, because gas stations can be few and far between; moreover at expressway speed in the teeth of a 60 mph wind like we had yesterday, mpg can be pretty low - like 35-40.) Predictability is more important than range, because with predictability you can plan your route and stops for fill-ups intelligently.

Your second point is important: it is a really bad idea to have a "fill it right now" warning with practically no reserve: the "fill it now" signal probably should be at 2 bars, where you might have 50 (who knows) miles in reserve.


Changing the subject a bit>>>


I just went to the gas station to top up, because I have to take friends 70 miles to the airport in the _really_ small hours tomorrow morning for a 'can't miss' international flight. I have no idea if the remaining 3 bars would get me there (is it 3 bars or 3.99 bars?). At that hour I don't want to take the time to stop for a fill if I get a "fill it" warning or worry if I will find an open station quickly.


I fill normally (at about 37F), the pump cuts off at about 6.5 gals, about the same as last time I had 3 bars, and I decide to experiment a bit by pulling the nozzle out an inch, expecting to fill only an inch of pipe. To my amazement it takes another 1.5 gals before shutting off. I remove the nozzle and a pint of gas comes gushing back out like I have never seen - followed by lots of big air bubbles.

OK, so I made a mistake - the gas pressure evidently forced the bladder to expand beyond its natural resilience. After it's through burping air, the gas level was still flush with the top ot the pipe, meaning that the bladder was still contracting as it burped. But why am I getting AIR burping out - it must have been there all the time and should have been displaced by the initial filling? Filling normally, I never am able to displace any air once the pump shuts off - activate the pump and it clicks off again immediately.

I know others have discussed this kind of thing, and that "topping off" (which I didn't really intend to do), is inadvisable, or that 'burping the tank' can get more in, but the incident tells me the bladder is a horrible design that results not only in inability to determine tank content, but is also prone to overflow in a manner you can't get with a rigid tank.

You ask me if Toyota is to blame: my answer now is "yes" for a horrible tank design and it's attendant problems, (not for "causing" a person to run out of gas, as someone suggested). I didn't feel strongly about tank issues until tonight - just curious; now I'm upset the system is dangerous - and not foolproof as it should be.

I'll probably get flamed for doing the wrong thing, but someone is REALLY going to get flamed, sooner or later: this mistake is just too easy to make.

 

the pump nozzle can create an airtight seal, leading to pressure buildup in the tank as the fill progresses, and gas gushing along with air burping.

hence my hope that this will be the last year that any car has a bladder tank. they've made a drastic improvement and i hope they use it more universally.

 

oh, and DH brought home the book with some good fuel system info in it... will be posting info from that early next week. at the moment i'm taking advantage of the couple days we have left to hang out before he leaves. well, at the moment he's asleep and i'm on the computer... but you get it.

 

the gas pump does not create an airtight seal. in fact the pump uses air rushing back INTO the pump to insure that there is still room in the tank. when that air flow coming back into the pump is interupted, it shuts off the flow of gasoline into the tank. if the pump did create an airtight seal, you would either have to vent to open air, which is not legal in this state, or back pressure would not allow ANY gas to go in.

if you look at the nozzle you will see a small tube. if that tube gets gas in it, it will cause the constant click off because the fluid in there does not allow air to flow back up into the tube which normally holds the gas valve open.

the reason why you got spit back has little to do with air since there is very little room in a colaspsible bladder for air to gather. put a one gallon bucket on the floor and pour a full gallon of water into it at chest height. the reason you spill water out has nothing to do with trapped air. the fact is, if you try to slosh in a gallon of fluids into a gallon container too fast, you will slop some of that fluid out. the bladder in the Prius being flexible just amplifies the problem. imm, the lack of air space in an empty bladder reduces the air flow back into the pump when filling making it tougher to keep enough air flow on the valve to keep pumping. that is why so many here have problems getting a full tank.

fill a glass of water to the brim, then toss a small rock into it. you should slop out water in volume equal to the pebble right?? ...well...that only works on paper.

 

hmm. i read that bit about the airtight seal somewhere here on PC...

interesting to know, dave. i never paid too much attention to the gas pump

 

the auto shutoff works on the bernouli (speeling maybe suspect) principle. the gas running through the large tube over the opening of the small tube, will create suction in the small tube. the small tube therefore sucks air into the large tube from the tank being filled. the air suction holds a check valve open which allows the gas to flow.

actually i have link in my blog...from a guy trying to explain how the shutoff mechanism works. i found this explanation rather clearer than others i have heard, and often wondered if shut off issues before the tank was filled was caused the the LACK of air pressure buildup.

here is his explanation

Pal, you're going to need a doctorate to understand the following, so cleanse your mind of distracting thoughts. In a gas pump handle you have two valves: the main valve, which is actuated by the oversize trigger you squeeze to make the gas flow, and the check valve, which lets gas flow out but won't let anything back in again, thus reducing fire hazard. In the seat of the check valve you have a little hole. To the backside of this hole is connected a Y-shaped tube. One branch of this tube runs down the nozzle and exits at the tip while the other runs back to a diaphragm connected to a release mechanism on the main valve. When you squeeze the gas pump trigger, gas running past the hole in the check valve sucks air out of the Y-shaped tube. (This is because of the Bernoulli principle: a moving stream of fluid tends to pull things in from the sides. Take my word for it.) As long the end of the Y-shaped tube exiting at the spout is unobstructed, air is simply pulled into the tube and nothing much else happens. However, as soon as the gas in your car's fill-up pipe gets high enough to cover the end of the tube, a partial vacuum is created therein, which yanks on the diaphragm, releases the main valve, and shuts off the gas. If the gas happens to be especially foamy one day, it may actuate the release mechanism prematurely, with the result that you end up with less than a full tank of gas. Simple, huh? Sure, just like nuclear fission. Stick with English lit.

now the foamy explantion i find a bit extraneous, but it also would make sense that if not filling a big empty tank (with a lot of air space which would provide a flow of air back through the valve equal to the volume of gasoline being put in) there maybe insufficient air pressure being created to hold the valve open.

this is the reason why i think many people have problems filling the tank. after the first shutoff, it seems like it takes a few minutes for the check valve to work properly again. unfortunately, the check valve is held open by the force of the rushing gas over the end of the tube, if you cannot get to full flow, that makes it difficult to reopen the valve...

ok anyway, i digress into another topic. hope all this makes sense

 

Thanks, Dave, your two posts are indeed very helpful, and makes perfect sense ( I do have the necessary PhD). A collapsed bladder contans little air, and so shutoff can occur prematurely, especially on fast pumps, which mine was. IF you pull the nozzoe out a bit, you create an air space, which permits renewed flow: probably the increasing weight of gas causes the bladder to expand, which is OK; the force of flow causes further expansion which is not OK, because when the flow stops, the bladder contracts forcing some of that gas out again. I still don't understand why I got a lot of air bubbling out afterwards, unless the fit of the nozzle is sufficiently tight to trap some of it in the tank I think it is, because excess gas did not spew out until I removed the nozzle. Perhaps if I had let the gas run more slowly, that would not have been a problem.

[I think one needs to dstinguish between the "airtight" seal around the outside of the nozzle, and the air flow through the Bernouilli tube].

The other issue I had is that the cut-off did not operate during the second phase of fill-up. The reason for that failure is not obvious to me: I would have expected excess gas to cause a cut off PDQ.

Next time I'm going to try pulling the nozzle back an inch, and topping off at moderate flow. When it clicks off, that's it. I don't want to overfill, and interfere with the scavenging system.

Galaxee, we are looking forward to your comments, after DH has time to digest the material he has, plus these posts.

C

 

i think the bubling is caused by the gas sloshing around while being filled. that causes the bladder to flex and stretch, causing it to alternately suck air in and out. on occasion, if the gas is shifted towards the filler tube at the same time air is being sucked out, that would cause the gurgling.

that is why when i fill, i never burp the the tank. i hold the nozzle in place for the time it takes me to round to the nearest quarter. that half a minute or so always seems to be enough.

seems to me, adding a one way valve at the opening of the bladder would stop any of this from happening...

 

well, i'm sitting at home, alone, exhausted, watching college hoops on a friday night and it occurred to me that i was going to post what i could find in the hybrid diag manual.

so they have a small blurb on refueling and what's going on where.

"When refueling, the engine is off and the EVAP VSV is closed (off). The resin bladder expands as fuel enters, so there is virtually no vapor space above the fuel. Hydrocarbon (HC) vapor flows from the secondary tank and fuel pump through the EVAP line to the charcoal canister. The HC is absorbed by and stored in the charcoal canister.

Air flows from the charcoal canister to the airspace between the metal outer tank and bladder and to the canister closed valve (CCV). The CCV is open, allowing air to exit from the fresh air valve. The refuel check valve and fuel cutoff valve work together to prevent overfilling and liquid fuel form entering the charcoal canister."

now for some definitions.

the EVAP VSV controls engine vacuum to the EVAP system, to remove stored HCs from the charcoal canister.
CCV can stop airflow into the evap system to seal up the system.
refuel check valve is located on the side of the main filler pipe, used to prevent fuel from entering the EVAP lines.
fuel cutoff valve is located near the upper end of the fill pipe on the EVAP lines, used to shut off the filler nozzle when the tank is full.

i've got a couple conclusions in mind, but feel free to discuss amongst yourselves if so inclined. my brain needs a weekend to recover from this past week :blink:

 

This Diagram may help visualize it.

Edit, Attached second diagram.

 

Great, some solid info. Thanks Galaxee, we were hoping for that! Enjoy your hard-earned w/e while we all chew on this.

Thanks for the diagrams, Tempus. Is that the float valve on the extreme right?

It's going to take someone a lot smarter than me to figure this out.

It appears the outer tank is an open system during filling, so allowing the bladder to freely expand (to the extent temperature and its flexibility allows); if so, the outer tank does not appear to be a factor affecting filling.

Thus tank capacity appears to be solely a function of the ability of the bladder to expand. It is not clear from the information available what triggers "The refuel check valve and fuel cutoff valve work[ing] together to prevent overfilling". Perhaps premature activation of these valves can prevent complete filling (defined as leaving air in the bladder - defined that way because bladder inelasticity can prevent a "complete" fill).

Just a couple of comments to get the ball rolling again.

I think there were 3 main questons:

1. Is there a way of getting a baseline for the amount of gas in the tank? - I think not, short of running out of gas, then putting a known amount in.

2. What is the relationship of fuel guage (bars) to tank content: is the scale variable according to the filled volume of the tank (itself a variable)?

3. Are there ways of more completely filling/expanding the bladder?

C