Is there a way to tell what size it is? My gas gauge has never worked so I have just guessed based on mileage assuming I have the 13 gallon but every once in a while I fill up and get 14-15 gallons so maybe it's a 20? When the original owner bought it he special ordered it with a bunch of mismatched options( 5 speed with leather power mirrors manual windows and locks )
Thanks in advance!

 

The XJ gas tank is 20 US gallons

 

They only made the smaller tank in the early years.

 

You can get an additional 5 gallons in there by extending the vent tube.
The disadvantage is I get leakage around the access port gasket. (replaced gasket)
I found the mod by doing a search....

 

Awesome...thanks everyone ...very helpful info on long drives....I was just being safe with the 13 gallon assumption since the Haynes said there were two options but now I'll start going further and see what kind of mileage I can safely get on one tank. And have a new baseline

 

XJs all came with 20gal tanks. The difference is the earlier years had the pickup tube higher up.

 

To test my max mileage I just filled up a 5 gallon gas can and drove the jeep till it sputtered to a halt.

 

not a great idea considering the gas actually cools the fuel pump. You probably shortened it's life a bit.

 

With 200,000 miles on the fuel pump I think mines immortal. But i do have a backup in my garage.
I'm prepared.