Leak at top of fuel tank

[diezelraccoon]

So my shop wanted $600 just in labor to drop and reinstall fuel tank. It has a leak at the top and only leaks when you fill it up. Once you top it off it starts to leak a bunch of gas dripping off the frame for about 5 minutes then it stops.

Decided I am going to do it myself. My question is what potential possibilities could it be where it’s leaking at top of tank? I am thinking some type of seal around fuel pump, or possibly around the filler hose.

 

[swathdiver]

So my shop wanted $600 just in labor to drop and reinstall fuel tank. It has a leak at the top and only leaks when you fill it up. Once you top it off it starts to leak a bunch of gas dripping off the frame for about 5 minutes then it stops.

Decided I am going to do it myself. My question is what potential possibilities could it be where it’s leaking at top of tank? I am thinking some type of seal around fuel pump, or possibly around the filler hose.

Could be a line or vent line but probably a rotten fitting. So you want to be prepared to replace the entire fuel pump unit along with the lock ring and gasket and maybe even the hoses that attach to it. Before you being, check the straps that hold the tank and their bolts, maybe spray some oil on them to get them ready to be loosened up, if very rusty, you might just get replacements ordered up. Depends on how long you want the truck down for.

When I don't want my truck down for more than a day in such situations, I buy everything I can think of and replace all or most of it to get the rig back driving as quickly as possible.

 

[89Suburban]

So my shop wanted $600 just in labor to drop and reinstall fuel tank. It has a leak at the top and only leaks when you fill it up. Once you top it off it starts to leak a bunch of gas dripping off the frame for about 5 minutes then it stops.

Decided I am going to do it myself. My question is what potential possibilities could it be where it’s leaking at top of tank? I am thinking some type of seal around fuel pump, or possibly around the filler hose.

Never heard of an o-ring failing on the fuel pump mount. If it is coming from that area most likely the the top of the fuel pump housing or the lines that come out of it it have rusted and developed pin hole leaks. Where the pump is mounted the tank is sunk down like a dish bowl shape. Any rainwater that gets up there just sits until it evaporates. Same goes for any fuel leakage. I would think if you had a leak at the fuel pump itself you would smell gas all the time but necessarily see it leaking down unless it is a bad leak.

Filler hose you just got to go under there and follow and look for leaks.

I suggest getting the rear of the vehicle up on ramps with a worklight and camera and start looking around those areas and taking pics. That is helpful for areas you can't see. Especially above the tank is very difficult to see or even reach to do a "feel" test for wetness.

Here is what mine looked like:

 

[89Suburban]

I buy everything I can think of and replace all or most of it to get the rig back driving as quickly as possible.

Highly recommend this plan of action with the parts.

 

[Fless]

Year? Flex Fuel or gas only?

Depending on your year, the gas fuel pumps (sometimes called modules) are usually different from the flex fuel pumps, so be sure to buy the right one. Quality matters if you don't want to be doing this multiple times.

The tops of the fuel pumps can rot out and @89Suburban covered that. I've had the tank on my '04 down twice, the second time with a bad gasket on the fuel pump (not sure if that was installer error or defective part). The Flex pump gasket is not an o-ring, it's a fairly fat rubber gasket. If yours is Flex Fuel, ping me for some tips on which lines need to come off the tank as you drop it. Not all do.

You should be able to crawl under and check the filler hose for leaking; no need to drop the tank for that.

If you can get an endoscope camera in there to take a look to see the condition of everything, you'll be much better prepared.

You'll likely need:
1. a new pump
2. a new lock ring
3. a bolt kit for the tank straps - Dorman makes a pack (#55157) and maybe new straps, depending on the condition
4. possible evap and fuel lines

I would recommend watching this video; it's not your model or year, but yours will be similar. He shows some of the issues that are possible with the fuel and evap connectors. YMMV Got questions, let us know.

 

[rockola1971]

Not uncommon at all to end up with a leaking oring for the pump module. The typical cause is the lockring has rotted out (salt is the culprit here usually) or some knucklhead replaced the fuel pump module without replacing the oring on the module. Never ever reuse that large oring that seals the fuel pump module to the tank. Also when people overfill their tank and keep testing fate, that causes the oring to start leaking too.

 

[diezelraccoon]

Year? Flex Fuel or gas only?

Depending on your year, the gas fuel pumps (sometimes called modules) are usually different from the flex fuel pumps, so be sure to buy the right one. Quality matters if you don't want to be doing this multiple times.

The tops of the fuel pumps can rot out and @89Suburban covered that. I've had the tank on my '04 down twice, the second time with a bad gasket on the fuel pump (not sure if that was installer error or defective part). The Flex pump gasket is not an o-ring, it's a fairly fat rubber gasket. If yours is Flex Fuel, ping me for some tips on which lines need to come off the tank as you drop it. Not all do.

You should be able to crawl under and check the filler hose for leaking; no need to drop the tank for that.

If you can get an endoscope camera in there to take a look to see the condition of everything, you'll be much better prepared.

You'll likely need:
1. a new pump
2. a new lock ring
3. a bolt kit for the tank straps - Dorman makes a pack (#55157) and maybe new straps, depending on the condition
4. possible evap and fuel lines

I would recommend watching this video; it's not your model or year, but yours will be similar. He shows some of the issues that are possible with the fuel and evap connectors. YMMV Got questions, let us know.

03 Tahoe, it can use flex fuel but I don’t use that. It’s been a Texas truck it’s whole life.

 

[diezelraccoon]

Not uncommon at all to end up with a leaking oring for the pump module. The typical cause is the lockring has rotted out (salt is the culprit here usually) or some knucklhead replaced the fuel pump module without replacing the oring on the module. Never ever reuse that large oring that seals the fuel pump module to the tank. Also when people overfill their tank and keep testing fate, that causes the oring to start leaking too.

I don’t live in the rust belt, I live in Texas. This Tahoe was made in Texas, bought, and lived its whole life in Texas.