Jeep Wrangler Gas Tank Conversion

From 1991-1995, Chrysler offered two different sized gas tanks for the Jeep Wrangler. One was a 15-gallon and the other a 20-gallon however, these two tanks were not different in size at all. The difference in some was a plastic vent hose that extended down into the tank which tricked the gas pumps and prevented more than 15 gallons of fuel being filled into them. By shortening this hose, the tank can hold the 20 gallons of fuel it was originally made to carry. This entire conversion process is about a 60-90 minute job and can be performed without removing the gas tank from your Jeep.

Put the Jeep on a jack stand.
Begin by raising the left rear of the the vehicle on a jackstand and removing the wheel.

Remove the plastic panel in the rear corner.
This is held in place by four plastic rivets. Three of them are visible in the picture. The fourth one is not hard to find. Remove the rivets by securing the outer portion in place while prying the center outward 0.25"-0.5" with a small screwdriver. The rivets will remove as whole pieces. Don't damage them because they're needed for reassembly.

Disconnect the fill vent hose from the tank.
This is done by removing the hose clamp and pulling the hose off the fill vent neck. You may need to pry it, but it's only held on with a hose clamp.

Remove the inner plastic fuel vent neck liner.
Inside the neck of the fuel vent hose, you can see a tube which lines the inside. This liner tube is made of hard plastic. It's about 9.75" long and reaches about 7" into the tank. Gas can not be filled beyond the bottom of this tube. Shortening it will raise the fill level of gas that will fit into the tank.

To remove it, you will need to pry it away from the sides with a small screwdriver and grab it with any small tool that offers a STRONG grip. A needle-nose vise grip is recommended (see next photo) because this tube is crammed in there TIGHT. In fact, removing this tube was the hardest task on this project. Some people removed this tube in sections by pulling out 3", then cutting it off, and pulling another 3" until the tube was completely removed.

After the liner tube is fully removed, you must have at least one piece of it that is 3" long to be reinserted.

Cut a 2.5" section from the liner tube.
The fuel vent neck on the tank must have a section of the liner tube pressed back inside to maintain pressure applied when tightening the hose clamp (during re-assembly). Cut a 2.25"-2.5" section and fit it back into the fill vent neck. You'll need a hammer or something heavy to pound it in.

Do not to use a metal hammer should you be unlucky enough to strike any steel parts on the vehicle and cause a spark near all the gas fumes. When pounding the liner tube back in place, leave about 0.125" protrude beyond the fill vent neck in case there's ever any reason to pull it back out in the future.

Reassemble everything in the reverse order.
Use the hose clamp to attach the fill vent hose to the fill vent neck, four rivets to reattach the plastic cover on the rear panel, and five lug nuts to mount the removed wheel.

Final notes.
Unless you've installed a sending unit for a 20 gallon tank, the fuel gauge in the dashboard will be inaccurate. Some people that have done this conversion claimed the gauge won't begin to show movement until there is 15 gallons in the tank. Others didn't show movement until 10-12 gallons remain in the tank and when the gauge reads 1/2, the tank was near empty. There could be a number of reasons for this, but if you want a true reading, then it will likely be necessary to install a 20-gallon tank sending unit.