Gas Leak from Top of tank?

My '96 XJ has a gas leak coming from the top of the tank. When I fill it up it leaks, especially if sloshed around on bumpy or steep roads or if parked on uneven ground. As the tank gets lower it's not a problem.

Where could it be leaking from the top? My FP is mounted on the side and is not the culprit. Previous owner said he replaced the tank in 2019 right before I bought it and it doesn't look old or rusted.

It's common for the sender/pick-up assembly o-ring to fail.

So on mine the fuel pump and sending unit are all one assembly and install on the side of the tank (I just replaced both last winter) and I verified that's not where the leak is coming from. I could see it dripping down from somewhere on the very top of the tank. I know some 96 models had a different fuel pump and sending unit that mounted on top. Is that what you are referring to or am I missing something?

You have rollover valves in the top of the tank. Perhaps one of them is leaking.

Look up a fuel tank on Rockauto and you'll see the picture with the holes.

I failed a CA smog test (evap) due to the rubber gaskets around the vent lines drying out. It never leaked fuel, but was bad enough to fail the pressure leak down test. When I pulled the tank, however, you could see staining where is was leaking.



Note that those gasket and the valves are extremely hard to come by,. My XJ is a 1995, so same tank as your '96.


David Bricker / SYR

I had the same problem with my '96, but it was because a P.O. had drilled holes in the top of the tank. Probably done with Tek screws, attempting to mount stereo equipment in the back. They had "repaired" the holes with Bondo. It may have worked for them for the short term, but it didn't work for me.

It's common for these to rust around the seam and stop leaking once you have less than half a tank. The skid plate and seam combine to trap damp dust and rust it out.

I don't think it's the seam since I watched it leaking from the very top of the tank but that's good to know.

So I guess I'll probably just replace the tank? I'm going to have to drop it to diagnose and if it's something that I can't readily fix I don't want to have to do it twice.

Thanks for the responses everyone, I'm update once I figure out where the leak is.

If you are dropping the tank, consider the vent mod.

UPDATE:

A few nights ago I pulled the Jeep into the garage and started reaching up on top of the tank. I reached up and could feel the tank vent valve that is above and to the left of the fuel pump (on the passenger side) and I could feel that the rubber grommet was basically disentegrated and several pieces of rubber came loose just from feeling around with my hand. Im pretty certain that's my problem so I ordered a new Fuel Tank Vent Valve & Grommet Kit. Will update this again when I replace it and see what I find.

Anak, is the vent mod you are suggesting the one for increasing fuel tank capacity?

Yes, its definitely something to think about!
http://gojeep.willyshotrod.com/HowtoFuelTank.htm

Yes.

Note that the OEM tank has a slightly different diameter vent tube than do the Chicom replacement tanks.

Also note that if you have large hands you may need to find a helper who can reach inside.

PO of my Jeep replaced fuel tank so it's likely the cheapest replacement tank. Here is the description of the valve/grommet kit I bought on Amazon. I'm hoping it's the right one since it says it's aftermarket not OEM?

Aftermarket Fuel Tank Rollover Valve & Grommet

Replace part number:5360058 911-060,contains 1 x grommet, 1 x fuel tank vent valve

Compatible with Jeep Wrangler (YJ) (1987-1995); Jeep Cherokee (XJ) (1984-1996); Jeep Comanche (MJ) (1986-1992); Jeep Grand Cherokee (ZJ) (1993-1996)

Package includes 1 x fuel tank vent valve grommet, 1 x fuel tank vent valve
It's an aftermarket replacement part,Not OEM one
Durable plastic construction,offering long service life
Fuel tank vent valve is designed to relieve pressure from your gas tank
This direct-fit replacements also prevent gas from spilling out of your tank in the event of an accident
Product information
Manufacturer ‎BOLEWIN
Brand ‎BOLEWIN
Item Weight ‎2.39 ounces
Package Dimensions ‎4.13 x 4.02 x 2.64 inches
Manufacturer Part Number ‎5360058
Additional Information
ASIN: B0B6NWQJD9

The description sounds right.

You will have to let us know if the actual product is any good or not.

UPDATE:

I finally got around to fixing my leaking fuel tank and once I dropped the tank it was very clear why it would leak from the top. The old vent seals were toast and the Previous owner had just globbed a bunch of RTV all around the two tank vent valves instead of fixing correctly. He used so much RTV that I could barely see the vent valves. That quick fix had failed badly so I removed both of the vent valves and used a razor blade to scrape off the excess to make a clean surface for the new grommet seals and vent valves. I did not have to reach inside the tank at all to install the new seals and vents, I just installed the seals on the tank first and stuck the vent valves down through to seat them.

Here are the correct grommet seals and vent valves for the 1996 XJ with the side-of-tank mounted Fuel Pump that has 2 vent valves on the top of the fuel tank.

Dorman Vent/Rollover Valve 911-060
Dorman Grommet Seal 926-820

It's a pain in the rear that they don't sell these vent valves WITH the grommet seals because they were hard to track down individually.

* The first vent valve I bought on Amazon was NOT a correct fit for my Jeep (See my link in post #13).

Thanks for everyone's input and I hope this info helps someone with the same issue someday.

Well Done Sir!!

Thank you for the part numbers.

That should make someone's life easier down the road.