Gas tank leaking all of a sudden

Hi everybody,
My fuel pump was replaced just before I bought my XJ, and it was done by the owner. In doing so, he forgot to hook up the sensor for the fuel gauge. I have not fixed this, so I have to go off of mileage to know when it is time to fill up. I always try to fill my tank so I know I can get my hefty 190 or so miles without running out. Well, yesterday, I was topping off my tank and I noticed that I had put more than 20 gallons in. I looked and there was a puddle of gas under the tank (none had spilled back out of the gas nozzle). Well, I had to be at work in 10 minutes, so I drove it to work. I left at the end of the day and noticed a very large puddle of gas underneath the tank. Great!
I drove it home (about 3 miles) and parked it on the other side of the parking lot where no one else parks. It leaked a little and then stopped this afternoon.
What should I look for? Did I do anything really wrong to my XJ's tank? It looked like it was either coming from the round plug where the hose comes out of the tank to feed gas to the engine, or the seam of the tank just below the round plug.
Any info you can give about fixing this would be very much appreciated.
Best regards,
Dave

Rust.

Rev

he might of forgot to hook up the vent line for the tank along with the gage

i would first check the hoses and such.. but sometimes dropping an older tank and reinstalling it will stress a weak/rusty spot... but i doudt thats it unless he knocked a hole in the tank.. probably the vent hose...
mike

Another possibility if the fuel pump was replaced is that the big O-ring on the sender was distorted, or damaged. You're supposed to get a new O-ring, but not everyone does, and it's pretty tricky to get the sender in with the tank in place. I've had many tanks rust out, and usually it starts with a little sepage. I've never had it open up that fast.

After I replaced my the fuel pump, I had a big time leak. Turned out the clamping ring that holds the fuel pump and tubing assembly in the tank was rusted pretty bad, and when tapped in to place, did not compress the big 0 ring seal enough to make a seal. Got a new clamping ring for about $5 from a dealer and that solved it.

Ditto on the Fuel Pump O-Ring. I replaced mine about 3 times and it still leaks. Make sure it's seated right or it'll leak. My fuel pump just died on me 2 days ago, so I'm gonna drop the whole tank to make sure the O-ring is seated properly. I'm tired of laying on my back. Good luck.

June said:

Ditto on the Fuel Pump O-Ring. I replaced mine about 3 times and it still leaks. Make sure it's seated right or it'll leak. My fuel pump just died on me 2 days ago, so I'm gonna drop the whole tank to make sure the O-ring is seated properly. I'm tired of laying on my back. Good luck.

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I did it in situ on my stepson's 93. Never again. It took numerous tries to get the pump seated right, and numerous more tries to get the clamping ring on, with the o-ring in place, and there was very little room to work. When it was all done I still wasn't sure for a while whether it was right until he'd run through a couple of tanks of gas without either running out at a quarter tank or springing a leak at 3/4. I'd much prefer to do it off the car, even though it's heavy and I'd undoubtedly have to fabricate new hanger bolts for the ones that always shear off.

Is the tank draining completely?If it is then I would say there is a leak somewhere on or around the bottom of the tank.
If not all of the gas is leaking out then I would say it was the seal also.

No, it doesn't empty completely. It appears to be leaking from the O-ring or the seam in the tank just below it. I plan to remove the enitre tanks and try to do it right. I'll get a new O-ring and take it easy with the bolts. I hope I don't break them.