When is tank really empty?

I believe the 3rd gen Prius has an 11.9 gallon tank. Unfortunately, I don't know when you're near empty.

 

I have never had the guts to run it until the fuel was gone
I personally just take the advice of the system and when it blinks it's fill up time. There's no reason to run to the last drop aside from pure curiosity.

 

It truly needs refilling when it starts blinking. You can drive farther at the risk of damage.

As the fuel pump becomes uncovered in the gas tank, it can overheat. You get to replace the entire tank.

Sadly, once they run out of gas, a surprising number of owners keep driving, damaging their HV battery for no real reason.

 

I understand a lot of the compulsive behaviors that car owners have but...............
this seeming obsession with getting the tank truly EMPTY before filling it up just doesn't make any sense.

I never let mine get below 1/4, which is about 3 bars.
Not only can "stuff" happen, like getting caught in a really BAD traffic jam but on many cars the fuel pump is cooled by the gas and running it empty can damage the pump. Then there is the infamous "bladder" problem on some early Prius models.

So my advice is: Fill it up before it gets anywhere near totally empty.
Depending on how much you drive that could mean that you will have to visit the station ....what, maybe 4 more times in a YEAR ?? And you will never have to worry about actually running out.

 

FWIW....

I've got 62,000 miles in type. (G3)
I drive until DTE = 0. Then I drive 20-50 more miles, or until I go by a gas station with clean restrooms and good, fresh coffee. IIRC, The last bar starts flashing at DTE=20.
Since my Prius is a work car, I usually time it at just about 500 miles per tank, since my trips are semi-predictable.


I usually put 10 gallons in, which makes my fuel burn rate easy to guestimate.
500 miles, more or less.
10 gallons more or less.

With all due respect to earlier posters, I think that the 1.8 gallons that are still in the tank when I refill are enough to cool the fuel pump. I've never...not once....seen or heard of a Prius needing a tankectomy for an overheated fuel pump.
If a dealership out there replaced one then I would be suspicious of the diagnosis, especially if the shop manager owns a boat.

It's your car.
It's your call.
I think that it doesn't really matter for most Prius drivers. Since the bottom 20-percent of the tank is not measured by the fuel gauge???
I think that you're going to be OK loading fuel when the last bar is blinking...even if DTE=0.

That's MY opinion.
Current street value: <$0.02

Good Luck!

 

IMHO -- THAT is the main reason to not run your tank too low. Why do you want to put up with the stress that you will probably contend with by running it too low and wondering if you will "make it" to the next gas station? When ours gets down to one PIP, we will fill up at the first opportunity.

 

The tank isn't really empty until fuel starvation causes the engine to quit running. Do you really want that to happen?

Most cars have a significant reserve or safety margin set aside on the fuel display to provide adequate warning despite mechanical variations, vastly different fuel consumption in different situations, and driver inattention. For the most solid numbers on a single individual Prius, read the very first post of this thread: [WARNING] Running out of gas (Gen III)

Beware that every individual car and driver and situation will produce different results, and we cannot say just how much different yours will be. How much problem or inconvenience will it cause you to guess wrong and run out early?


[NB: Much of these road section lack cell phone coverage, so don't count on being able to call ToyotaCare or AAA for help.]

 

And who is to say that every place where it is ~100 miles to the next gas will have a sign posted ??
Letting it get real low is just NOT a wise thing to do.

 

Cars should treated like airplanes: NEVER fly/drive them until the gas tank(s) are EMPTY.

 

While I'm all for conscious fuel planning, your view is more extreme than I'd take it. Aircraft pilots seem to know their fuel supply down to about 10 or 15 minute accuracy, and are in a real heap of trouble if they run dry. Automobile drivers have far more flexibility, and the car makers leave far more uncertainty in the fuel gauge. One of my past cars accidentally ran dry with the gauge still above 'E', while another read 'E' more than two hours before burning down to its claimed tank capacity. This much uncertainty would be intolerable in aircraft, sharply reducing usable cargo capacity and range.

I've experienced several situations where knowing the approximate actual fuel range of a car is extremely valuable. (Does anyone remember when cars had much shorter ranges? When most stations closed at nights/ Sunday / holidays? When regional power failure shut down all area pumps? The odd-even-day fuel rationing during the 1970's gas crises?) Since then, I've intentionally run two cars dry to calibrate their tanks vs their gauges, without problems. Bob Wilson, who runs out of gas for fun and sport and engineering curiosity, mentions nearly fifty such events in his two Prii for a variety of his tests, and hasn't yet reported any serious consequences.

 

Hmm, so running out of fuel in rush hour on a bridge is not serious? How about running out on a secondary road on a Sunday, when all the gas stations within 100 mi. are CLOSED? (been there, done that, put 75 l in a 60 litre tank after sweating for about 90 min on the highway - in a Subaru). Or how about running out on a busy interstate?

When not traveling I fill up at 1/2 tank. When traveling I fill up at 1/4 tank min.

You can gamble if you like.

 

Back "...in the good old days ('50-60's)..." gas tanks were typically 'sized' to permit 8-hours of driving at 50 mph, or a range of 400-miles per tank. Of course, the same-sized tanks were used in 6-cylinder and 8-cylinder vehicles, which meant 8-cylinder models usually DID NOT go 400 miles per tank, while 6-cylinder models EXCEEDED 400 miles per tank.

...and, of course, gasoline was only about 25¢ per gallon.

 

Are you responding to me?

My intentional out-of-fuel tests were planned for very low traffic, low hazard conditions. No rush hour, no bridges. Bob's descriptions were similar.

Sounds familiar. The triggering incident for me was not only a Sunday, but also New Year's Day (1984). Some holiday plan changes left me a bit flat footed, departing without the usual topped-off tank, so I planned to refill early just 50 miles down the road.

Well, only one of the usual stations there was open. The clerk demanded a separate 'pump unlocking fee', equivalent to half a tank of fuel. And made it clear that it could not be split with the other customer who walked in at the same time. We both walked out. I sweated the next 130 miles.

By figuring out how much range subsequent cars really have, I can now comfortably decide whether to go the next segment without sweating, or backtrack or change route, or pay the price gougers, or just camp out until stations reopen or (future) Oil Embargo Rationing schedules allow me to purchase fuel.

With the old car above, if the gauge was as low as 1/2 tank, the car would not have made it to the next known open station. I would have had to pay that extortionate clerk or backtrack quite a ways. Some subsequent cars have had vastly different fuel gauge patterns. No single simple rule could be written to cover all those cars without paying the excessive fuel prices at the tourist traps and remote price gougers.

 

This get's asked quite often.
My experience is that the Gen 3 Prius gas gauge is very conservative.

I usually ignore the blinking pip, and drive until the DTE reads Zero. Then I fill up. And it's always even then a long way from empty.

It's not a hard rule though. If I get down to 1 blinking pip and fill up? Then I put in less gasoline and immediately am paying less.

But I feel Distance To Empty is a perfectly safe standard. I can easily go to zero and still have a good gallon or more cushion.

 

I wish. After running out once in my old car (same car as previous post), with the needle still above 'E', I would not go more than 250 miles per full tank.

With two 1970's era oil shortages still in fresh memory, I wanted a car that could go the 400 miles between my apartment and my parent's home refuge (a farm with a big tank on-site) without refueling, in case odd-even gas rationing or holiday closures made fuel unavailable at the particular time I wanted to travel. That old car just couldn't do it. The next could, in theory, but fell short in practice (pre-hypermiling). The next did it easily. The fourth fell quite short if I went strictly by the gauge, but did it easily once I figured out that 1/3 of its actual range was below the fuel gauge's 'E' mark.

The current household fleet can do it easily, but old lessons don't quickly fade away.

 

I vividly remember the green/red flags/pennants that were flown along with the even/odd of the 70's era so called shortage. The lines were ridiculous. Even with the company signs on the vehicle, it was insane just the waiting in the lines. And at times it didn't matter what time it was because the stations were NOT open all night long the way it is today. Even those that had posted hours on the door could not be relied upon because you never knew if they were flying red or green flags that day. To make matters worse, there would be times when the flags would change color from green to red while you were waiting in line. No more gas today at that station. What to do? Go get in another line and wait some more. Truly insane.

 

Even though the thread title is "When is Tank Really Empty?" I was assuming the OP wasn't really wanting to run the vehicle to empty...which isn't a good idea with any vehicle and especially a Prius.

I was assuming the real question was when do you really need to refuel? Or what is a good benchmark for knowing when to safely refuel.

While I feel perfectly confident driving until the DTE says Zero...I would never advocate for somebody to REALLY drive until they reach the "real" empty.

 

I fill up when I get down to half. You never know when the unexpected will happen, like earthquake/tornado/hurricane/wildfire. You never know when you'll have to drive a long way without gas available, and you'd feel a bit silly sitting on the side of the road because you tried to squeeze the last 2 miles out of the tank. Maybe it's from living in earthquake country and years of working on computer networks, but I always try to be ready for the unexpected.

 

My apologies to anyone who took my post as directed to -them-. It's directed to anyone who, for reasons I just can't understand, feels they -must fully drain the fuel tank- until they fill it.

And if my examples of problems that can arise doing this are too real to understand, perhaps some fantasy problems will be easier.

The zombies are after you and you run out of fuel. Munch munch.

The Clingons are coming and you must run but you are out of fuel. Zap zap.

The end of the world is nigh but you can't make it back to your family to say goodbye because you are out of fuel and all the fuel stations are closed.

Yes, I think anyone who intentionally does the run to empty for other reasons than measurement are fools.