[WARNING] Running out of gas (Gen III)

Applied as a blind rule over my long driving experience, this common 1/4 tank rule fails.

On a past car, the driving distance from the 1/4 gauge mark to fuel starvation was much shorter than the length of some gasless stretches of road I travel. Fortunately this was discovered very close to home.

But on another car, still in my household, a large portion of the advertised tank capacity is below this mark. The range above is annoyingly short. Faithful adherence this rule means paying inflated tourist trap prices at the start or end of those long gasless stretches. And completely unnecessary.

Has anyone else traveled a long sparsely-served road, during holiday hours when most stations were closed, and faced a clerk demanding a surcharge to unlock his pump?

Does anyone else remember news from the 1973 oil crisis? In states with alternate day gas rationing, people could not legally buy fuel every other day. Numerous families who had to make long trips on specific days were making extraordinary efforts to make those trips possible. Some were caching the family's second car along the route beforehand, swapping mid-trip, and retrieving later.

Because of those and other situations, I want to know what my cars can do, at least to certain distances that I'm likely to need. If one never uses it, it isn't really there. But always test beforehand, when the consequence of failure is minimal.

 

That is a minor issue for me. The primary matter is the uncertainty of how gauge 'E' relates to the real bottom or advertised capacity of the tank. Among my past and present cars, the spread between most optimistic and pessimistic gauges is about 1/3 tank, roughly 5 gallons.

Put into aviation terms, in a previous thread, a pilot made a point of tracking remaining fuel load to about 10 minute accuracy. Among my cars, the bottom-of-tank spread has been more than 2 hours. (The first fill of 'my' first car accidentally ran dry above E. The next car was intentionally run dry once, going 2 hours beyond the same gauge position. One car still in the household, though never run dry, goes even farther beyond E.)

And this is at average burn rate, before accounting for the greater variability in cars than in aircraft.

 

Where do I obtain a calibrated fuel dipstick for my car?

I'm not making excuses for people who habitually and unexpectedly run out of gas. But the initial fuel gauge calibration provided to drivers is not on the same order of magnitude of accuracy that pilots can get with their sticks. (See my previous posts for the spread I have experienced.) We have to expect some drivers, whether by accident after changing cars or by design as they practice with the lower ranges of the fuel gauge, to mess up once or twice.

I test only under conditions where help is within a short walk. The triple-digit stretches with no services are planned to fall within previously proven fuel range with margin that is comfortable with me.

 

Well that is what the miles to empty feature is all about, however; any rule of thumb requires common sense. If you drive in Ohio, Indiana, Pennsylvania and Illinois like I do its plenty of fuel especially in a Prius with a 120 mile range on empty, if you live in the west crossing the Mohave, or Alaska driving the Alaskan highway you have to apply the common sense factor differently of course.

Not running out of gas is a common sense issue no matter what you drive.

 

Most pilots don't own one, and many I suspect have never even seen one. The typical GA pilot fills the tanks up to a pre-determined limit (tabs or to the top), use the book's value of gas tank to determine flying time/range. the trick here is:

1) The book lists "unusable fuel", i.e., fuel that is present in the tank but is not guaranteed to be useful at all flying attitudes/conditions (typically a gallon or so)

2) The Federal Aviation Regulations (FAR) mandates a specific, minimum reserve fuel (30mins in day, 45mins at night, with more for instrument conditions)

It's not so much the accuracy of a fuel gauge - we're taught not to rely on that. Instead, it's the common sense of giving yourself some working error of margin. By maintaining a reserve - whatever you set, be it 1/4 tank, 200 or 50 miles, etc. - you guard against inadvertent out of fuel situations. Of course, the larger the margin the better the odds against you running out of fuel but the more frequent the fill ups.

Keep in mind that in the best of circumstances, where you've planned everything out, conditions may still change, e.g. engine runs excessively rich for some reason, and you may still find yourself out of fuel despite the margin.

Nevertheless, that's the whole point of keeping a reserve, never dipping into it unless your engine is not working properly, there are no gas stations available, or you know there is a preferred station coming up at a nearby distance.

Lastly, if you monitor the miles driven, then you can even discern when the engine is running too rich, tank leaking, etc. I've noticed in my VW 2001 that the malfunctioning mass air sensor makes it run leaner than normal - my range has extended significantly from before. Nevertheless, I plan all my trips with the more conservative estimate because at times the MAS does work properly and then the engine uses more fuel than I would have accounted for.

As long as its reasonably accurate, I'm fine with any type of fuel gauge (analog or digital). If you insist on driving the vehicle to the margins of its performance limits, then you might want to check out ScanGauge or similar instrument and see about creating a custom "fuel totalizer" instrument which estimates how much fuel has been burned over time by examining the fuel injection timing. I think only airlines/corporate jets go to that extreme and even then they have a staff of people backing them up (including meterologists) to ensure that they have sufficient fuel, and even then..I bet they have ample room for error.

 

No requests, however - I'm glad to see the results!:cheer2:

 

Bob,

I enjoy all of your posts. Don't know if you're an engineer, or not, but your approach to things is very analytical, and thorough. At times, that's a huge breadth of fresh air on this web site.

Keep it up!:thumb:

 

I think the most interesting data to gather would be pulse and blood pressure of the operator.

Perhaps decibels of any co-owner/partner/spouse, as well.

 

Glad I spotted this thread, I figured my new Gen III was like my Gen II. Ran out of fuel twice with my old one. Coasted in to a station with a dead traction battery the last time

I noticed no difference in the car after abusing the battery like that. Car was totaled so I'll never know if the battery life was affected.

Lovin my new one, loaded up 5.5 GB of music on a flash drive and plugged it in last night, excellent. I have more audio entertainment options than I know what to do with

 

"Unintended De-acceleration"

I had my first loss of power episode this morning. Slight uphill grade @ speed in 65 zone, went all the way down to 42 getting off to he right in heavy traffic. I never suspected it might have been fuel (180 miles till empty) or so I thought by the guage. I rebooted (I am a computer tech) so I thought any PCU prob. would benefit from a cold rreboot. I did that twice and set off in PWR Mode with guages showing engine running and got to work. I had them tow it to the dealer because I agree that this type of behavior is dangerous. 4600 miles on OD, getting 51 avg and as high as 68 when I really baby it! I joined to voice this concern about "Unintended De-acceleration"

 

First off, I find if amazing that this thread has gone on for 14 months and 40 pages of post!

I find it more amazing that I actually just sat here and read all 40 pages of posts...

But, the most amazing thing is that NO ONE has commented on the loss of power steering when the ICE runs out of fuel and shuts down!

Any one else find it even a bit curious that a vehicle with a large battery will run the electric A/C with the engine off but not the electric power steering?

In the event of having my ICE shut down at speed (regardless of the reason), I think I'd be more comforted knowing my battery would keep my power steering running rather than my A/C! I'm just saying...

 

Is this true? I would like to hear this confirmed by one of our trusted technical members.

Tom

 

Personally, I'm trying to deceide if I'm pathetic for even reading the whole thread. I don't own nor am I looking at purchase a 2010 Prius. :loco: I was just :bored: at work yesterday afternoon.

 

I learned from you that the power steering is 12 volts, which makes sense because there were off the shelf 12v power steering units available.

We all know the 12 Volt battery is a pathetic little thing.

Might the sudden shutdown when you run out of gas be Toyota's unwillingness to let the driver kill the 12 volt battery by using the power steering with a run down traction battery?

Thank you for doing your test work, more knowledge is good.

I noticed something interesting on my last two tanks. The last bar started blinking at approximately 40 miles remaining. In one case I was making a sharp turn (I don't remember which direction), in the other case it came on as I backed down my mildly sloped driveway and dropped off my rolled curb.

After the last bar started flashing at approximately 40 miles, I deliberately drove on near level ground with gentle starts, stops and turns. After several miles the last bar stopped blinking. In both cases the bar started blinking again right at 20 miles to empty. I'm at 1/2 tank now, I will see if I get the same results next time.

During the whole process, the miles to empty number decremented in a reasonable looking way. Since I can only find one fuel level sender in the parts beakdown, shop manual or electrical diagram, I think it's reasonable to assume the bars and miles to empty both indicate based on the same sender and at the least use very different time constants to filter the signal.

Keep up the good work and remember the 10-20-70 rule

10% of the people make things happen
20% of the people watch things happen
70% of the people wonder what's happening.

 

I still don't have my car yet, (I was promised delivery today, but now it is next week), but from scanning this thread I am finding out that in lieu of a low fuel light the last bar on the fuel gauge starts flashing when low, and I would have about 2 gallons left? That seems to be consistent with the other Toyota vehicles I have owned, with the exception of the Tundra where the low fuel light comes on with 6 gallons left!!!