Been doing a lot of work to the Jeep and suddenly there’s a new sound. With the Jeep on a lift and fuel sloshing back and forth in the tank I can hear a fairly loud rattling noise that just started. It sounds like something broke loose and is floating around in there banging up against the inside of the tank. Everything works fine otherwise. Any ideas?

Well, if it's in the tank.I guess you gotta drop the tank and see what it is. Can't be good right?

Yep, gotta drop the tank, take a look.

Yeah

Darn it! I was hoping someone would say that this was common and nothing to worry about.

I mean you can tell yourself that. And if its running fine and your fuel gauge is working... give it a try... But I would just yank the tank off and find out.

If you haven't had it out in long while, I would be prepared with new filler neck hoses, clamps, and pending the condition of the support straps I would have those ready too. That way you can do it all at once and no extra trips to the parts store or delays waiting for the parts. If the fuel pump is from '98 and still working fine, I would stick with it - those OEM parts are better made than todays aftermarket. But if you need to replace the pump in the future, with the new straps and filler neck hoses - it will be super easy and go by quick.

Let us know what you find in the tank!

I’m not going to say it’s normal but mine has been doing it for as long as I’ve owned it. 6-7 years.
i can shake the xj and hear it. But it runs fine and it never caused a issue.

let us know what you find if you drop it

Unless you have a locking gas cap it's always possible someone decided to mess with you and dump something down the fuel filler. It happens

An older guy I know once told me about his buddies pranking him with a few ball bearings dropped in his tank. He said you would hear them clack every time you stopped the car and take off again.

This is a fairly new car for me. I bought it as a non running project. This is the first time I've filled the tank to the top which I assume is why I never heard the noise before. It's going to be a while until I've used up enough fuel to make the tank easy enough to drop.

You mentioned the tank is full - in that case, I expect this is normal.

There's a rollover protection valve in the tank - IIRC it's basically a ball valve that blocks the fill pipe if you roll over, stopping gas from leaking.

When the tank is full, that ball rattles as fuel tries to slosh up the fill pipe.
It's a funny noise, and my '98 has done it for the last 20 years when the tank is 90%+ full.

This is more than likely the explanation.

My 1998 does it when it’s not full. Everything works so I never took time to drop the tank.

God bless you

My '98 had a clunking noise from the fuel tank when the tank was mostly full. I assumed it was the float for the fuel level sensor rocking around with the fuel motion. I recently changed the fuel pump because the fuel level sensor quit working.

Examination of the float assembly in the old pump showed it could move side to side and hit against the fuel pump housing. The new fuel pump's design did not allow the side to side movement of the float. There is no clunk/rattle with the new fuel pump. I can hear a whine of the new pump if I am standing near the back of the Jeep while the engine is idling.

In my case the clunking/rattling was benign. I ignored it for 50K miles.