Gas gauge is seriously off

ZMachado

New Member
Joined
Nov 21, 2020
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6
Location
Los Banos, CA 93635
Backstory on my Jeep before I get into the meat and potatoes of my situation: bought my TJ 1 year ago. 2006 Wrangler X, 6 cylinder, 4-speed auto. Came with a 3.5” lift on 33s that were mud tires. Fast forward to now, it’s a year later and I’ve been researching possibilities about why my fuel gauge seems off. I always fill up at 1/4 tank, and when I do so it’s usually about 11 gallons. I know TJs came with 19 gallon tanks, but at 1/4 tank it seems I should be filling up more than 11 gallons. How do I tell if my gas tank is not 19 gallons? Or do I just have a super bad fuel gauge?
 
When the gauge hits the red you still have four or so gallons of fuel left. 4+11+4=19
That's quite a large reserve.... I just wonder if that 4 gallons is accessible once your gauge hits the red....
Although with 15+ year old vehicles there is probably quite a lot of junk residing on the bottom of the tank.
 
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That's quite a large reserve.... I just wonder if that 4 gallons is accessible once your gauge hits the red....
It is. The gauge doesn't control the fuel pump.
Although with 15+ year old vehicles there is probably quite a lot of junk residing on the bottom of the tank.
I guess that it depends on the vehicle's history. My tank was surprisingly clean when I fixed the valve.
 
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It is. The gauge doesn't control the fuel pump.
I understand the gauge doesn't control the fuel pump, but the point I was trying to make is IF the fuel pump pickup is close enough to the bottom of the tank to actually avail of the remaining fuel....
The most fuel that I have added when filling the tank with the Low Fuel indicator illuminated is 13 gallons.
 
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Maybe drive it to empty with a gas can in it to get you to the station. then fill up when you know exactly how much you put in it from the can
 
Maybe drive it to empty with a gas can in it to get you to the station. then fill up when you know exactly how much you put in it from the can.
Thanks for the recommendations, but I am not curious enough to know how much fuel can be added once the fuel pump loses suction to risk drawing in sludge into the fuel pump and injectors from the bottom of this 21 yr old tank.
 
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I understand the gauge doesn't control the fuel pump, but the point I was trying to make is IF the fuel pump pickup is close enough to the bottom of the tank to actually avail of the remaining fuel....
The most fuel that I have added when filling the tank with the Low Fuel indicator illuminated is 13 gallons.
The fuel pick up isn't close to the bottom of the tank, it is exactly at the bottom of the tank in that small sump. I'd be astounded if you have more junk in the bottom of the tank than you can wipe out with a couple of paper towels.

The low fuel light trips when there is roughly 4-5 gallons in the tank. You can easily prove me wrong by carrying a small gas can and driving until you run out of fuel and then filling it up all the way. ;)
 
Thanks for the recommendations, but I am not curious enough to know how much fuel can be added once the fuel pump loses suction to risk drawing in sludge into the fuel pump and injectors from the bottom of this 21 yr old tank.
If it was going to draw in sludge, it would already be doing it since the filter sock is the absolute lowest point in the tank. That said, if something loses suction, how does it suck in sludge?
 
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I've read on the internet, so it must be true, that the reason for the conservative reserve it to keep the fuel pump submerged for cooling. This seems reasonable to me. I've had several vehicles with a 4-5 gallon reserve, and occasionally driven the vehicle long after the gas gauge registered empty. My fuel pump did not die. YMMV.
 
I've read on the internet, so it must be true, that the reason for the conservative reserve it to keep the fuel pump submerged for cooling. This seems reasonable to me. I've had several vehicles with a 4-5 gallon reserve, and occasionally driven the vehicle long after the gas gauge registered empty. My fuel pump did not die. YMMV.
The internet yet again is full of poo. The pump sits in a canister that gets filled when the tank is above a certain level. Barring that, there is a check valve that lets fuel into the canister to the same level as the fuel in the tank. Even if you run it completely out of fuel, the pump is still sitting in a canister full or relatively full of fuel depending on how much you can slosh out. That and 5 gallons would not submerge the pump due to the size of the tank and how high 5 gallons would bring the level to.
 
If it runs out & "loses suction" cycle the key on & of several times to re-prime. This isn't rocket surgery. haven't you ever run out of gas before? It doesn't render the vehicle dead
 
My fuel gauge is hilarious. It takes about 20 miles for it to go from full to 1/2. When I first got it I pulled over shortly after I filled it up because I assumed I was dumping fuel.

Then it hangs out at 1/2 for about 100-ish miles where it promptly drops & triggers the low fuel light. Hangs out there for another 50 miles or so before I fill it up.
 
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2004 owner’s manual:

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When my warning light comes on, I have about 5 gallons left. I’m not sure why the manual claims 2.