Why even get to that point.
I never have less than a 1/4 tank at any given time.

Besides the fuel pump is happier when its submerged in fuel.

 

Not really an answer to my question, but thanks anyway for this insight.

 

I'm sure it is different but if it helps ........
I have a 3.6 and I have made it at least 15 miles ( Light came on and I was able to get to a gas station before the car cut off.)

 

I started a thread elsewhere on this same topic......I had 50 showing on my Distance to Empty, and when I filled the tank, turned out I only had 2 gallons left in the tank. I'm guessing that if I had taken it all the way to zero, I'd have run out.

Low Fuel Warning means.....Low on Fuel!!

Took my 19 Trailhawk on a road trip this weekend. Almost home, got the "Low Fuel" warning on the gauge cluster. The DOE was showing 45 miles. The fuel gauge showed a bit under 1/8 of a tank. When I filled the tank, I put 22.4 gallons in the tank, which means I had ab bit more than 2 gallons...

www.jeepgarage.org

Re: keeping the pump submerged, that is an old wive's tail. First, the fuel tank is baffled to keep the fuel pump submerged at all times, even with low fuel. The only risk you have is that there is less fuel to dissipate the heat that the pump is putting out. Second, the amount of heat the fuel pump generates is minimal; it is a small electric motor, and that doesn't generate a lot of heat. Third, the amount of time you actually drive with the tank low is minimal compared to total time. The old adage "keep your tank at least 1/4 full or you'll burn your fuel pump out" is simply a trick by service people to have an excuse to change your fuel pump. "Hey, have you run this thing low on fuel lately? You did? Oh man, you should probably replace the fuel pump, it's about to fail now!!"

That being said, I seldom let my tank go below 1/4 tank. But that is simply so that I don't get into a situation where I need to go somewhere quick, and I have an empty fuel tank.

Keith

 

Not an old wives tale.

Depending on how the pump is made, it is the pump itself, not the motor that runs the pump, that can suffer. It is true, pump motors are built to withstand occasionally getting low on fuel and losing it's cooling. There is usually still fuel enough to splash around and keep it cool. The part that actually does the pumping does not like to get hot, seals can get damaged quickly. It is not just heat that causes problems with running low on fuel. Debris and even water in the tank will get sloshed around when the fuel is low where it normally would be settled in the bottom.

There is a filter screen to protect the pump from being damaged by large chunks but the filter screen can get clogged. With the pump sucking air when the screen is clogged or low on fuel will cause cavitation. Cavitation in a fluid can be very damaging. If you've ever seen pitting on the lower unit and propeller of an outboard motor, a lot of that is caused by cavitation. This also causes a vibration. Vibration in a pump is extremely damaging.

Modern fuels are better designed to handle some water and keep it suspended, but being low on fuel in high humidity or cold weather condensation can accumulate some water in the bottom of the tank. Fuel pumps do not like pumping water.

 

Agreed, 1/4 tank and fill up.
Dont play Russian roulette to see which bullet it is..

 

The other thing....
The filter gets cloged from all the [emoji2959]
So quarter tank & fill ,yessss...

 

I almost always wait until the low fuel warning indicator comes on before filling. I figure what's the use of having a 24.6 gallon tank if I'm only using 3/4 of it.

Anyway, when the low fuel light comes on I look at the miles left until empty on the screen and plan accordingly. Usually, it says there's 45-50 miles to go.

 

Haha, never over estimate the Jeep designers. You'd think that a vehicle especially made to travel off-road into the wilderness would've made their 'low fuel light' give you enough get to a place where you'd get fuel? Dial back to the year 2000, with my brand new GC Ltd on a spectacular trip, with friends, into the Richtersveld, in the Northern Cape, South Africa. Never had the light on before but there it was, brightly shining in my eyes. "OK guys we need to plot a course to a fuel station", huh? Found out it grounded the Jeep within less than 20 miles and the nearest Fuel at least a 100 away.

 

I'm pretty sure my light comes on with about 3 gallons left in the tank. Your DTE will vary based on the current mpg calculated by the computer. 50 miles is a good assumption, unless you are offroading and crawling the trails. As Rickvr said, you can burn up fuel pretty quickly off road.

 

I've run my '19 until the fuel light comes on several times and then another 10 miles or so to get to a station and I've never been able to put but 21 gallons and change into the tank. Figuring a 24 gallon tank plus a tad in the filler neck I'd say there is 3 gallons or so when the light comes on. It's almost identical to what I found on my '11.

 

Whenever my low fuel light comes on the tank only takes 21 gallons. On the highway at 19 mpg that's still 60+ miles remaining, enough to get to the next service plaza or an exit with decent fuel.

 

My old 2500 06 Chevy, 18 miles hauling a trailer. My new Ram hauling the same trailer, 68 miles and didn't run out. My 03 GC went 43 miles and didn't run out.

 

I ran out of gas ONCE with my wife of 40 years . . . .when that light comes on, I know I'm in trouble . . . .keep gas in it and the wife happy.

 

Depends on which way you're driving going uphill/downhill or what side is lower than the other... Yeah... You can get fuel delivered, but how long do you want to listen to the whine of tiny voices or the boss saying I told you to stop miles ago.

 

SRT (6.4) - About 30miles left when light comes on
Trackhawk (6.2) - About 20miles left when light comes on

At that point you want to drive very "ECO" when light comes on because you don't want to lean the engine and\or be stranded.

 

I have a limited, and there is a sub guage that will tell you so get into the menu

 

On my 2014 GC Limited I actually ran it out of gas to check the accuracy of the remaining mileage system. When the remaining miles hit Zero the engine stopped. It is accurate! Since it has electric power steering I didn't need to worry about losing power steering. That worked great also. BTW don't try this without carrying a full can of gas so you can get to a fuel station.

 

You can switch to the Fuel Economy (or is it fuel management?) page in the EVIC, it will tell you distance till empty when the low fuel light comes on. Obviously the distance till empty is an estimate, your actual mileage may vary. As well, the count down of miles till empty will stop around 25 miles and just state "Low Fuel", my guess part liability and part they can't accurately estimate DTE anymore at that point.

IMO, being a 100 miles from the closest available fuel, and waiting till the low fuel light comes on before planning on getting fuel, sounds like a Driver/Operator Issue and NOT a Designer Issue. You might note the aftermarket has lots of options for mounting fuel cans for off-roading in remote places.

Low fuel not cooling the fuel pump? The WK2 and many vehicles of the last 20 years has the fuel pump inside a plastic reservoir tank that is part of a fuel pump assembly. The fuel is drawn up into the reservoir tank and the return dumps into it, to keep the fuel pump submerged in fuel, until you're truly out of fuel.

An actual electric fuel pump, most look very much like this....

The WK2 electric fuel pump assembly....

Notice the big plastic cylinder, the actual fuel pump is much smaller and mounted inside that big plastic cylinder that is a reservoir tank. I suspect the real reason they have gone to this design is more that having a much, much smaller reservoir tank within the tank, that can hold about 3-5 minutes of fuel for the engine, is so that if you're running low on fuel in the tank and have to drive up a hill, you won't run out of fuel as the gas in the tank shifts away from the pick up and uncovers it. Anyone that has driven an older car, running low on fuel, and had to go up a long hill, will tell you that is where they ran out of gas. But the fuel pump will be immersed in fuel right up until you run out of fuel.

Have you ever seen an electric fuel pump mounted outside the tank? Designed to be mounted that way? They look no different than the in-tank mounted pumps. Why do they not overheat from not being immersed in fuel?

So I have my suspicions about running low on fuel runs your fuel pump hot and shortens it life. Most cars of the last 20 years or earlier, have their fuel pump in a reservoir that constantly keeps it immersed in fuel until you completely run out of gas. Oh, if your going to speculate the reservoir is not much gas, so it doesn't cool well enough you need the entire tank of gas, the reservoir is made out of plastic, a poor thermal conductor, if the tank is full, not much heat (or cooling) is moving through the reservoir to the 24 gallons of fuel in the tank.

Do I know for a fact that the fuel pump needs to be immersed in fuel to remain cool or NOT? No, I don't? But I have never seen anything authoritative stating its true, its just something people say and speculate as to the reason why. And then I see plenty of contradictions to the concept.

Dirt clogging up the pick up screen/filter? I suppose its possible, but I have opened 2 different gas tanks more than 10 years old with close to or more than 200k miles on them, and they were spotless inside. That doesn't mean every tank is spotless inside.

Condensation I can see being a big deal and it would be worse in a lower fuel level tank. I wonder if plastic fuel tanks have less condensation than metal tanks?

 

If a filter screen is unimportant, why would a vehicle manufacturer waste money and time putting them on the fuel pump?

Wondering if plastic condensates like metal? Super easy experiment, even you can try this, take a metal cup and a plastic cup fill both with ice and water. Does condensation build on both cups? Spoiler alert. As you correctly noted, most plastics are decent insulators. The plastic cup will sweat less, but it will sweat. It's not just condensation on plastic, some fuel additives, MTBE in particular, are hygroscopic. Hygroscopic means: Readily attracts water from the surrounding environment. BTW, the fuel itself (with or without MTBE, in a plastic or metal tank) will condensate, also.

I know you have no idea if a fuel pump is immersed in fuel to keep it cool. Have you ever asked someone who has worked on the design of fuel systems, why fuel pumps are immersed in the fuel? Rhetorical question. Not only have I talk to somebody on the design of fuel systems I am an engineer and I have worked on the design of fuel systems. Cooling is one of the factors to keep the pump submerged in fuel, but not the most important and not the only reason.

Not only have I seen an exterior mounted fuel pump, I have two of them sitting on my bench, right next to an in-tank type. The external type fuel pumps are nearly the size of a beer can. The internal types aren't much bigger than a pill bottle. I'll let you speculate on why size matters...

 

I ran out at 17 miles. Hardy any warning.

 

When my fuel low chime comes on at 20 miles left, I look at miles in tank remaining and judge accordingly. I have managed to go for 6 miles with it on 0 the once though, and managed to get to a fuel station with my expectation it'll cut out at any moment and yet it didn't.

 

Just tested this in the Nevada desert with a huge trailer 😅; 50 miles to the nearest gas when the empty warning went off.

Found this post when the anxiety hit so though I’d post for posterity

2014 3.6: exactly 3 gallons

 

2016 Trailhawk, I drove very conservative for 26 miles after light went on and it went dead empty.

 

It seems like everybody has an estimate but it looks like I'm going to have to actually drive mine once the fuel light goes on hit the odometer and drive until it runs out with a spare can in the back because nobody apparently has done this and nobody knows exactly how many miles everyone says 20 to 50 30 to 60 2 gallons 3 gallons left somebody actually knows and speak up assumptions are like assholes everybody's got one

 

Good luck, 'dirtyredg' Let us know. What model do have, exactly?

 

The low fuel light goes off at 1/8th of a tank of fuel.
Considering, its a fuel "Level" gauge and not a fuel Quantity gauge, it is telling you the level of fuel in the tank, not the actual quantity.
It's not very accurate and not well calibrated.
And your mileage will vary drastically with the conditions and how you drive.

When the low fuel goes off on a WK2, you have roughly 3 gallons in the tank, and that could vary more than a little.
That is roughly 42 miles for me, perhaps farther on the highway.
The counter will just go to low fuel 25 miles because there are just to many variables to predict when you'll exactly run out of gas.

Low fuel light means find a gas station, that is all its good for....