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The "Front-Line" Perspective
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Hey guys, I've got a question that I can't find an answer for:

In a Ram 1500 with the 121L Tank (larger tank option) what is the "reserve", or to put simply - when the gas light comes on, and the range to empty becomes "low" what is the standard for the amount of gasoline remaining in our trucks?

Thank you,

Rob
 

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Typically, the low fuel light comes on in most cars with 1/8 tank left. For my 1992 Dakota with optional 22-gallon tank, I find that it comes on when I have 4 gallons left. Your mileage may vary.
 
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Virginia Gentleman
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I have a 2006 1500 with the standard 26 gallon tank (US gallons). Low fuel light on the dash comes on with about 2-2.5 gallons left at about the 1/16 mark on the gauge. The "low fuel" indicator on the overhead when the avg mpg is displayed doesn't display until there's about 1-1.5 gallons left in the tank. Either way, you'd better be looking for fuel. The closest I came to empty was when I put 25.5 gallons in. That was cutting it too close for comfort. I try to never go below 1/8 tank.
 

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It's a good idea not to go below 1/4 tank routinely, because the fuel pump relies on the fuel surrounding it to cool it. There is correlation between constantly running the tank near empty and early fuel pump failure.
 

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Virginia Gentleman
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Depends on how you define "early pump failure". My Ram's original pump failed with 229K miles on the odometer earlier this year and I am the original owner. Replaced it with a Carter. That's the longest I've gone on a fuel pump. My '92 Acclaim's pump failed at about 145K miles.

On a normal week, it usually gets down to somewhere between 1/8-1/4. I rarely go below 1/8.
 

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There is no absolute standard. It varies by a gallon or two from truck to truck.
 
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Got parts?
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It's a good idea not to go below 1/4 tank routinely, because the fuel pump relies on the fuel surrounding it to cool it.
Bob, when I recently replaced the pump/sending unit assembly, the interior of the original one was just about full with gas, even though the rest of the tank was just about empty. Perhaps they're designed so that fuel is constantly surrounding the pump, which is inside of the assembly, unless and until the tank is completely empty (or down to pints rather than gallons remaining). I think your advice is sound, but the design may help protect the pump, except in cases of extreme negligence.

Regarding the OP, on my '92 Dakota, before I replaced the assembly, the warning light came on with about 2 to 2.5 gallons left (approximately 8 to 10 liters). The junkyard assembly I replaced it with is designed differently, with a larger pick-up filter on bottom; the light now comes on with about 4 to 5 gallons left. So when the light comes on might depend on the supplier who makes the assembly.
 

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KOG
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The certain way to know is to carry a 5 gallon (20L) fuel can with you and run it until it quits, noting the distance you could travel after the low fuel light came on. Then put in the can and proceed to the nearest filling station. Another technique is to note the size of the tank, and see how much fuel it takes to refill it immediately after the low fuel light comes on. Not quite as accurate as you're never sure exactly how much usable fuel a tank holds until you run it out. After having several pumps on minivans fail at 180-200,000 miles I've started replacing them at 150K to avoid being stranded in the road.
 

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Bob, when I recently replaced the pump/sending unit assembly, the interior of the original one was just about full with gas, even though the rest of the tank was just about empty. Perhaps they're designed so that fuel is constantly surrounding the pump, which is inside of the assembly, unless and until the tank is completely empty (or down to pints rather than gallons remaining). I think your advice is sound, but the design may help protect the pump, except in cases of extreme negligence.

Regarding the OP, on my '92 Dakota, before I replaced the assembly, the warning light came on with about 2 to 2.5 gallons left (approximately 8 to 10 liters). The junkyard assembly I replaced it with is designed differently, with a larger pick-up filter on bottom; the light now comes on with about 4 to 5 gallons left. So when the light comes on might depend on the supplier who makes the assembly.
Mine is the factory original and comes on at 4 gallons left.
 

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I noticed that the messages of miles to empty went from displaying the miles remaining to just saying low fuel around 40 miles. I think my 2012 Challenger was the first to do that. The older ones just kept showing fewer and fewer miles until they hit 0 (not that I did that often but occasionally I did).

So my guess is somewhere around when DTE hits 40-45 miles you get the low fuel warning. This is a different function than the old style low fuel light and appears more precise (i.e.: based on calculated miles left and average economy rather than a set amount of gas in the tank).
 
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Virginia Gentleman
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I noticed that the messages of miles to empty went from displaying the miles remaining to just saying low fuel around 40 miles. I think my 2012 Challenger was the first to do that. The older ones just kept showing fewer and fewer miles until they hit 0 (not that I did that often but occasionally I did).

So my guess is somewhere around when DTE hits 40-45 miles you get the low fuel warning. This is a different function than the old style low fuel light and appears more precise (i.e.: based on calculated miles left and average economy rather than a set amount of gas in the tank).
Our Journey does the same. I don't believe the Ram does. The one time I did run it to almost empty (~0.5 gallons left) the DTE was displaying less than 10 miles. I'll have to check the DTE the next time the low fuel light comes on (if I ever let it get that low).
 

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KOG
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The 09 T&C does the same of just displaying "low fuel", no mileage display. You have to guess how many miles you have left. Usually low fuel comes on when the display hits about 30 miles remaining and you really have about 50.
 

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Hey guys, I've got a question that I can't find an answer for:

In a Ram 1500 with the 121L Tank (larger tank option) what is the "reserve", or to put simply - when the gas light comes on, and the range to empty becomes "low" what is the standard for the amount of gasoline remaining in our trucks?

Thank you,

Rob
The fuel level gauge aren't very accurate, they just don't have the time on the assembly line to calibrate the fuel level gauge, they are built to be reasonably accurate without calibration, so they vary quite a bit from vehicle to vehicle.

The whole system is just designed to be accurate enough to prevent you from running out of gas.

The "low" fuel light should come on at 1/8th of the fuel level, meaning now is the time to find gas.

If you really want to know how much fuel is left in your tank in your vehicle, since it can vary by several gallons from vehicle to vehicle, when the low fuel light comes on, fill up the tank, subtract the amount of fuel required to fill the tank from the tank capacity for your fuel tank, that will give you the quantity your low fuel light goes off in your vehicle. (another vehicle it could go off as much as several gallons different than yours).

Keep in mind;
The tank capacity does NOT include the filler neck, as much as a gallon of fuel can fit in the filler neck from the refueling port to the tank. So when you fill the tank, don't keep topping it off till the fuel level is to the very edge of the refuel port, you'll add a gallon into the calculations.

You're engine will fuel starve and stall before you've drained every drop of fuel out of the tank, at some point, while there is still fuel in the tank the pick-up will start to suck in air with the fuel and cause the engine to start to run awful, cause its fuel starved, eventually it will suck more air than fuel and the engine will NOT run, but you might still find some fuel in the bottom of the tank.

Most newer vehicles, with the fuel pump in the tank, have a reservoir in the fuel pump assembly, i.e. a small tank inside your tank. It sucks up fuel from the main tank and puts in the reservoir and the fuel pump pumps fuel out of the reservoir to the engine. This keeps you from running out of gas on a hill, where the fuel might slosh to one side of the tank and uncover the pick-up from the fuel. i.e. the motor can run a few minutes on the gas in reservoir if the fuel sloshes to one side of the tank and can't be sucked up by the pump. Eventually the fuel has to slosh back and cover the pick-up to refill that reservoir or the engine will stall from fuel starvation.
 

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Virginia Gentleman
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Along with what Rick has posted, I suppose you could install a fuel pressure gauge. When the gauge twitches (or shows a significant pressure drop) that would indicate the tank is just about empty. Most hi level race cars (NASCAR in particular) don't rely on fuel gauges (too much variance). They have a fuel pressure gauge. If they are trying to stretch a fuel run as far as they can, the driver may wait until he sees the fuel pressure gauge twitch or drop pressure. That's a good indication they are just about out of fuel.
 

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As stated before, while the low fuel light may be triggered by an amount of fuel (usually 1/8th) remaining in the tank, Distance To Empty (DTE) is a calculated number that will dynamically changed based on estimated gallons left and past observed gas mileage. So if you're driving in exclusively town, the DTE displayed will be less than if the exclusively on the highway. Likewise the DTE switching from a displayed mileage to LOW will happen with more gas in the tank if you're only driving in town vs. driving on the highway.
 

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Most of my vehicles, the low fuel light was pretty darn close, it was 1/8th of the capacity of the tank. So a twenty gallon tank, I knew when the light went off, I had 2.5gal left in the tank; if it was a 12.5gal tank, I had a little more than 1.5gal left. I did this with my subtraction method of refueling the moment the light went off. I also didn't keep topping off to get an even dollar amount, once the pump auto-shut off, I noted the gallons added before it auto-shut off.*

My '95 Cherokee and '02 Caravan read lower than actual quantity, again the calibrations or rough since there is no final calibration after install, so they seem to bias toward reading lower than actual quantity, i.e. less likely for owners to run out of gas, which is a better result. Both vehicles had twenty gallons tanks and actual quantity was closer to a quarter than an 1/8th. So I had a good 5gal left in the tank when the low fuel light went off, and more like the low fuel light quantity when the fuel gauge pegged at the bottom.

When I replaced the fuel pump on my '95 Cherokee (it was old enough that the fuel pump doesn't come as one whole assembly with the level indicator). I recalibrated the fuel level sender on it while the assembly was out of the gas tank. I simply held the assembly next to the tank roughly in the position it would sit when mounted in the tank, moved the float full up and down and could tell, just like the gauge would show, that it hit the top limit before the top of the tank and never hit the bottom limit, hitting the bottom of the tank first. I bent the rod to the float a little so that it limits of the float where the same as the top/bottom of the tank, again biased a bit toward reading lower than actual quantity. Sure enough, a much more accurate fuel level gauge resulted, that still bottomed out on the gauge before actually running out of gas, but the low fuel light went off pretty close to 2.5gal left in the tank.

I've hadn't have to pull the fuel pump on the Caravan, my kids drove it as their H.S. car, and surprise, surprise, when I check the car the gauge is always pegged on "E" and when I ask if they are going to put gas in it, they always say, "Awww, you can go another 60 miles when the gauge hits "E", I still have plenty of time before having to add gas."

*At least for me, I've observed that the gas pump will auto shut off when the foaming gas hits it. For the most part, when the tank fills the foam is forced up the filler neck and hits the pump tip to auto-shut it off. So if you stop at that moment, you've got pretty close to a full tank with very little in the filler neck. When you wait a moment, and pump another 20cents, repeat several times, what you're doing is waiting for the foam to settle to add fuel to the filler neck and fill to the top of the filler neck.

I saw a Jerk raise holy hell with the gas station owner, cause his pump showed that he filled his vehicle with more gasoline than the tank could hold. He admitted he came in on fumes with the vehicle bucking from fuel starvation. But the vehicle owner was insisting the gas station owner was ripping him off, by mis-calibrating his pumps to show more gas than is actually pumped out. I intervened and explained about the filler neck being able to hold up to a gallon and would explain perfectly the mismatch on the pump numbers. The gas station owner even brought out the calibration jug and pumped out 5 gallons into the jug and it game out right on the line down to the 1/10th of an once. The guy still said we didn't know what we were talking about and he was still ripping him off. What an ^(&*()&*)(, cause I know the word filter would ding me!
 

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KOG
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Bottom line on all of this: unless you have calibrated the gauge in that individual vehicle you really don't know how far it will go after "E" or "low fuel".
 

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Yes, but you can have a better idea if you're just a bit observant about your vehicle.

I already explained how you can figure out pretty close what quantity is left in the tank when the low fuel light goes off.
You can do the same when the gauge hits "E" as well, to learn that amount.
You can observe your fuel economy based off different conditions.
Assume when your down to a half-gallon left in the tank, you might fuel starve and stall anyway.

So you can do some quick math in your head and know when you're likely to run out of gas when you hit the warnings.
That is what a computer does when you have a Distance Till Empty (DTE) display, and when the margin of error for the different variables becomes to great an effect, it just displays "Low Fuel", so owner's don't make warranty claims or file class action lawsuits cause you ran out gas in the woods 2 miles before the DTE display said you would. Once you hit the point of its anyone's guess, plus 25 mile or more margin to cover the manufacturers butt for liability, it just says "Low Fuel" meaning it could be any minute you run out of gas.
 
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