How many gallons are in the tank when the dash "LOW FUEL" light comes on?

[Larry N.]

Larry, is the 'unusable' amount there to collect water that can be drained off? Regards Steven

No. It's the shape of the tank vs the fuel pickup point. Aircraft fuel tanks have drain valves at the low point, and you drain a small amount each time during preflight to check if there is any water- if so, you MUST get it out of there or risk an engine stoppage in flight, rather less than desirable.

 

[Tulecreeper]

On my 2019 RAM the fuel light icon comes on a little below 100m range remaining. Then around 30m remaining I get "Low Fuel" enunciation. At about 10 miles the range goes blank. I have put more than 26 gallons in the 26 gallon tank.

I've also put more than 18 gallons in my 18 gallon Jeep tank. Missed the exit on my fuel stop at night and the next gas was more than 30 miles away.

Similar thing happened on my MH. First thing happened was the genny quit. I thought, "I should be good to get through Atlanta (heading north) and fuel at the first truck stop. I was mentally calculating remaining gallons and mpg but I was using the wrong total gallons. I am sure I pulled into the pump on fumes.

I normally don't do that. I figure at 1/3 tank I am "on reserve" and need to fill at the next suitable station.

This is true unless you let your 25 year old kid routinely use your truck. I always get it back near empty no matter how much it starts with.

Unless I am going cross country I never put more than 10 gallons in any more. Then he "has" to fuel it - LOL..

My old man told me, "You can use the car/truck as much as you want, but if I ever get in it and find less gas than when I got out of it you won't use it again."

I ran out of gas one time. Luckily, I was a block from a gas station so I was able to put it in neutral and coast in. Unluckily, I didn't have any money on me. I had to call a friend to come to the station and lend me enough money to get enough gas to get home where I got money from my room and went back to another station and filled up. Then I had to go pay the friend back. Lesson...and embarrassment learned.

 

[Tulecreeper]

Pay attention to what your gauge reads when to begin to fill up, then mentally keep track of how much you put in and after a while you will know how many gallons you have remaining no matter where your gas gauge sits.

I had my last truck for 20+ years and I could tell within .5 gallons how much gas it would take solely based on where the needle was sitting. Used to amaze people sometimes. Pull into the station, look at the gauge and say, "Better get gas; going to need about 16 gallons." <5 minutes later> Pump: "Clunk" Them: "How much did you need?" Me: "15.89 gallons." "How did you know that?" <grin>

 

[Ex-Calif]

My old man told me, "You can use the car/truck as much as you want, but if I ever get in it and find less gas than when I got out of it you won't use it again."

That works for me until I want him to do something for me... I suck at setting boundaries - LOL...

My favorite pilot saying, "3 things that are useless to a pilot are the runway behind him, the altitude above him and the air in his gas tanks."

Due to stronger than forecast headwinds I almost ran out of gas on a cross country flight. I was pretty inexperienced and got focused on the flight plan vs. finding a suitable alternate as soon as I calculated it would be closer than it should be.

I think I put 30 gallons in what is supposed to be 32 total gallons of tank.

 

[Old_Crow]

Pay attention to what your gauge reads when to begin to fill up, then mentally keep track of how much you put in and after a while you will know how many gallons you have remaining no matter where your gas gauge sits.

I had my last truck for 20+ years and I could tell within .5 gallons how much gas it would take solely based on where the needle was sitting. Used to amaze people sometimes. Pull into the station, look at the gauge and say, "Better get gas; going to need about 16 gallons." <5 minutes later> Pump: "Clunk" Them: "How much did you need?" Me: "15.89 gallons." "How did you know that?" <grin>

I tend to start looking for gas once the needle is past the 1/2 mark. Usually end up filling at about 3/8 of a tank. I've gotten to where I can guess pretty accurately how much it'll take to fill my 75 gallon tank.
On the Jeep, it has the 19 gallon optional tank. When the light comes on, it'll take 15 to fill it.
On the bike, when I have to turn it to reserve, it'll take 4 gallons to fill it.

 

[Skookum]

While we're sharing anecdotal evidence, we estimate we have ~25 gallons left when our fuel light comes on. We have two 50-gallon saddle tanks for 100 gallons total capacity. The light comes on at around 1/8 tank remaining on the gauge.

Either the gauge is woefully off, or Freightliner does this for "severe service" use where the engine is using maximum fuel, like the equivalent of getting 3mpg if the vehicle is moving. Our average is about 8mpg or a little less. We just mentally calculate that we should have ~100 miles until we need to find fuel when the light comes on, worst case, leaving a good margin of safety. If we're only getting 3mpg, that would be 75 miles of reserve. at 8mpg we'd have 200 miles of reserve. It is a real pain if you run a diesel engine out of fuel, so we're usually filling up when the gauge is not quite down to 1/4 as we never want to be in that situation.

 

[Alan_Hepburn]

Our 2007 Bounder on the Workhorse W22 chassis has a 75 gallon fuel tank. When the Low Fuel light comes on it will take 60 gallons, so we've got a 15 gallon reserve. We try to never see that light - it's a lot more relaxing to drive on the top half of the tank.

 

[Ex-Calif]

The light comes on at around 1/8 tank remaining on the gauge.

Either the gauge is woefully off, or Freightliner does this for "severe service" use where the engine is using maximum fuel, like the equivalent of getting 3mpg if the vehicle is moving. Our average is about 8mpg or a little less.

It would be interesting to know the algorithm for my truck's computer. There is an mpg since last reset button and there is some sort of continuously computed number that goes into the remaining range calculation.

I have noticed that if I have been driving around town a lot and the avg. mpg is like 17 the full tank range can be as low as 450 miles or so immediately after a refill but if I immediately get on the freeway for a trip the range number starts climbing so that 20 miles later it might be closing in on 500 miles. It's kinda weird to watch the range increase as you burn fuel - LOL...

OTOH - If I have reset the average and done a long freeway leg (21.X mpg) the range is about 550 miles after refueling.

 

[Tulecreeper]

It would be interesting to know the algorithm for my truck's computer. There is an mpg since last reset button and there is some sort of continuously computed number that goes into the remaining range calculation.

I have noticed that if I have been driving around town a lot and the avg. mpg is like 17 the full tank range can be as low as 450 miles or so immediately after a refill but if I immediately get on the freeway for a trip the range number starts climbing so that 20 miles later it might be closing in on 500 miles. It's kinda weird to watch the range increase as you burn fuel - LOL...

OTOH - If I have reset the average and done a long freeway leg (21.X mpg) the range is about 550 miles after refueling.

My 2500 does the same thing. It's because we are getting better mileage at 60 MPH than we are at 35 MPH. I get 25 MPG at 60, but only 12 MPG at 35. I notice that my average MPG goes up the longer I stay at freeway speed, so of course my range will increase along with that.

It's been almost 2 months since I picked the truck up and my lifetime average MPG still hasn't hit 14.5 yet. It's because I spend most of my time at 40 MPH, or less, just putting around the backcountry here and only make a couple trips a month into "the city".

 

[Lou Schneider]

IMO, "Low Fuel" is just another idiot light catering to people who don't pay attention to the vehicle they're operating. "Hey dummy, it's time to look at your gas gauge!"

 

[Skookum]

It would be interesting to know the algorithm for my truck's computer. There is an mpg since last reset button and there is some sort of continuously computed number that goes into the remaining range calculation.

I have noticed that if I have been driving around town a lot and the avg. mpg is like 17 the full tank range can be as low as 450 miles or so immediately after a refill but if I immediately get on the freeway for a trip the range number starts climbing so that 20 miles later it might be closing in on 500 miles. It's kinda weird to watch the range increase as you burn fuel - LOL...

OTOH - If I have reset the average and done a long freeway leg (21.X mpg) the range is about 550 miles after refueling.

It's an interesting split. I believe the "low fuel" lights are based on the resistance reading from the fuel sending unit and the light comes on at the exact same point every time, i.e. "You have 3 gallons left! Use them fast, or use them slow, but you've been warned!" The light might come on and go off a few times based on the changing uphill/downhill slope of the road.

The range estimates in the dash display are calculated using various data from the ECM. It's interesting how many miles can still be driven even when "Distance Until Empty" is 0 miles. Speaking from experience as a passenger, of course

 

[Larry N.]

have noticed that if I have been driving around town a lot and the avg. mpg is like 17 the full tank range can be as low as 450 miles or so immediately after a refill but if I immediately get on the freeway for a trip the range number starts climbing so that 20 miles later it might be closing in on 500 miles. It's kinda weird to watch the range increase as you burn fuel - LOL...

As you are pulling out of the station, you are idling and/or running in a low gear, with some acceleration, thus the mileage is lousy, but as you get in a higher hear and settle in to a steady speed the mileage improves dramatically.

The scangauge on my F-150 has an"average" mpg and an "instantaneous" mpg, and it's interesting to watch how they change (gph, too). The built-in gauge with the truck computer is also an average since last reset. The "computer" tracks the last 400 or 500 miles as a base for the average, so when you reset the gauge it starts at idle, which is zero mpg, and gets better rapidly from there. Essentially the same with the mpg "window" on my Ventana -- it climbs rapidly -- but the more miles in the "base" the more slowly it changes.

 

[NCSU Dad]

#1 - Note to self when adding a locking gas cap to RV immediately put the gas cap keys on the ignition key rings.

After the gas cap key fiasco where I had to drive home to get the cap key the tank took 51.2 gallons after letting the nozzle click off a second time. So that left me with 3.8 gallons remaining in the 55-gallon tank with the gauge needle right next to the "E" line marker. That's no accurate indication of gallons remaining when the low fuel light came on since I had driven 30-40 miles with the light on. I'd estimate maybe 7-8 gallons in the tank when the low fuel light came on.

I do not normally drive with so little gas in the tank. I was running the tank down to get as much 1 year old gas out of the tank before filling with fresh.

Thanks again for the replies!

 

[TheBar]

Any modern vehicle needs to be kept above 1/4 or the fuel pump in the tank gets overheated and can cause failure.

 

[garyb1st]

Our Pace has a 75 gallon tank. I've never seen a low fuel light. But then I've never added more than about 55 gallons at one time. The needle stays on the full mark until I've used about 10 to 12 gallons. Depending on conditions that could be 60 to 80 miles of driving. Not sure but maybe that's also the way it works when it hits the Empty mark. Most days we don't drive more than 250 to 300 miles and we'll fill up in the morning before hooking up the toad. We have the typical quarter tank generator cut off level and while I've never tried, that's one way you could tell. I have a greater concern for what's at the bottom of the tank than actually running out so I don't let it get too low.

 

[Ray-IN]

That works for me until I want him to do something for me... I suck at setting boundaries - LOL...

My favorite pilot saying, "3 things that are useless to a pilot are the runway behind him, the altitude above him and the air in his gas tanks."

Due to stronger than forecast headwinds I almost ran out of gas on a cross country flight. I was pretty inexperienced and got focused on the flight plan vs. finding a suitable alternate as soon as I calculated it would be closer than it should be.

I think I put 30 gallons in what is supposed to be 32 total gallons of tank.

No rest areas nearby?

 

[Ray-IN]

Our Pace has a 75 gallon tank. I've never seen a low fuel light. But then I've never added more than about 55 gallons at one time. The needle stays on the full mark until I've used about 10 to 12 gallons. Depending on conditions that could be 60 to 80 miles of driving. Not sure but maybe that's also the way it works when it hits the Empty mark. Most days we don't drive more than 250 to 300 miles and we'll fill up in the morning before hooking up the toad. We have the typical quarter tank generator cut off level and while I've never tried, that's one way you could tell. I have a greater concern for what's at the bottom of the tank than actually running out so I don't let it get too low.

Your pickup tube isn't near the tank bottom?

 

[Ex-Calif]

Thanks to everyone for mansplaining that if you press on the long board harder your mpg goes down - LOL...

I reckon Skookum is right that the low fuel light is based on the float level in the tank.

The remaining range is based on whatever the current algorithm is calculating. The RAM has a graphical bar for instantaneous mileage. I didn't like it at first as I am a digital guy but it does show "better" how the foot is related to the MPG.

I does make me accelerate slower most of the time. I also know if I bury my foot, the truck leaps and the instantaneous pretty much goes off scale low - Gotta love a big block hemi - LOL...

 

[Onyrlef]

Isn’t this kind of like how much water will a container hold or how long is a rope?

 

[whiteva]

Airplanes and hwy vehicles get very silent as the last of the fuel is used. Of course then the real noise begins as the passengers/DW start to holler "what did YOU DO"

"Running on fumes is very hard on the sphincter ."