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Gas tank wont fill up all the way.

ZJeepX

ZJeepX

NAXJA Forum User
Location
San Clemente, CA
My tank will only fill up about 17 gallons. Any ideas of why?
Im sure its a 20 gallon tank but I have only gotten it to fill up all the way once like a year ago. I didnt do anything special that one time I just got lucky haha.
 
mines like that, but a rock or two and a stump helped me a little
 
The tank in the XJ is sold as a 20 gal tank. However, the internal vent in the tank causes the pump nozle to shut off before the tank is full. There is (should be) an air space between the top of the tank and the gas in it to allow for expansion on hot days. This is to prevent the fuel from spilling on the ground on those tripple digit summer days.

I too seldom get more than 17 gallons in my tank even when the gas light is on.
 
Unless you run out of gas, or drain it, how do you know that you don't have 3 gallons in it before you start filling? Mine takes 17 gal when the light comes on, but I just thought it still had 3 gal in it. Sounds normal to me. Should be able to drive about 50 miles more before you're walking.
 
techno1154 said:
The tank in the XJ is sold as a 20 gal tank. However, the internal vent in the tank causes the pump nozle to shut off before the tank is full. There is (should be) an air space between the top of the tank and the gas in it to allow for expansion on hot days. This is to prevent the fuel from spilling on the ground on those tripple digit summer days.

I too seldom get more than 17 gallons in my tank even when the gas light is on.
Click to expand...

nice answer very much the same thing I have experienced in the 4 xj's I have owned
 
No problems getting 20gal in all three of my rigs.
 
My 98 really annoys me, it'll only take 14 gallons when the light is on and it gurgles for 2 or 3 days after I fill it up. I think it also has some sort of goofy electric pump on the evaporative system. It's an ex-gov vehicle, so maybe it has some special configuration
 
RCP Phx said:
No problems getting 20gal in all three of my rigs.
Click to expand...

I highly advise not running around on fumes. Not to mention condensation in the tank, it is bad for the in-tank pump to have air passing through it when the last fuel sloshes around the pick-up. The fuel pump is rated and tested pumping fuel. Pumping air causes them to "over-rev" and can cause bearing damage to the pump. The Ford pickup trucks have an issue on this because most of them for the last 20 years have 2 gas tanks. People run the first tank to empty and switch to the 2nd tank. THis causes a high rate of pump failure. I try not to run below 1/4 tank to prevent this.
 
Maybe that is the case but my gauge has never gone to full except that one time. I should have explained better sorry. It always stays right above 3/4 tank when i fill up all the way. So I figured 17 gallons would be right above 3/4 tank. Always thought the gauge was working right. Maybe my gauge is just broken.
 
I am not sure of this or not. But I do believe I heard that depending on the year of the XJ, the filler neck location on the tank is in two different locations. Depending on the height it will either fill all the way up to 20 (if the neck is at the top of the tank, or only to around 17-18 ( when the neck is located down the side of the tank).
 
xjboy said:
I am not sure of this or not. But I do believe I heard that depending on the year of the XJ, the filler neck location on the tank is in two different locations. Depending on the height it will either fill all the way up to 20 (if the neck is at the top of the tank, or only to around 17-18 ( when the neck is located down the side of the tank).
Click to expand...


Interesting. :)

On my XJ, the fill tube is about 3" above the bottom and the vent tube is about 3" below the top of the tank.
 
FWIW, I've never gotten more than about 18 gal in my 88. That included filling up the neck as well.

The pump inlet does not go to the bottom of the tank. There's also a vent line inside. If you search, you may find the posts that cover changing the vent tube to raise it a bit and get a bit more fuel into it.
 
Don't know what year you are driving, but the 1990 Electrical Service Manual says the resistance of the fuel sending unit should be 1 ohm at empty, 44 ohm at 1/2, and 88 ohm when full.

If the sending unit is good, then your guage needs calibration.

Also, anybody have a 13.5 gallon tank? The 1984-2001 Haynes manual says the 13.5 gallon is standard and the 20 gallon is an option. Might just be an error.
 
MJ's came with 13.5 Gallon tanks. Long beds came with 13 gal. tanks, shortbeds came with 18 gal. tanks. I have a long bed and have never gotten more than 14 gallons in it, including the filler neck.
 
I usually try to fill up no later than when I get down to 1/4 tank remaining. From there it takes around 12 gallons til the pump clicks off. I did drive around with the fuel light on long enough to make me nervous once (I have NO idea how far it will go once light comes on). That is the most I've ever put in the tank in a single fill and it took just shy of 14 gallons. There are no dents or anything on the tank. I'm pretty sure that it wont take 18 or 20. Any other tank options besides 13.5/18/20?
 
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