Fun one here.

About two months ago, I noticed that my gas gauge was stuck at 3/4 full. I suspected the sending unit because disconnecting the probe made the gauge immediately register empty and turned the low fuel warning light on. I found a used replacement sending unit and swapped it out with the tank at about 1/4 capacity. Lo and behold, the gauge now read 1/4 full and it seemed I'd found a simple fix for the issue.

…Until I topped off the tank. Fuel literally spilled from the sending unit's threaded seal with the tank, which is positioned about ~1 gallon below the top of the tank in terms of overall position (see attached photo). It all flowed through the gap at the bottom of the unit, which is highlighted by the yellow ellipse in the photo. I'll leave the calculation of approx. how much gasoline ended up on my floor pan and ultimately drained through to the garage floor as an exercise for the reader.

So, the easy conclusion is: I'm an idiot and I stripped the threads on the unit or the tank itself installing this, or forgot a second gasket. Thing is, the unit, which is a long metal cylinder with a float contained within, can only fit in the tank one specific way; it has virtually no play once inserted. And the unit I bought had a single collar gasket, which I put into place before threading it home.

Anyone replaced this unit and had no issue whatsoever? My short-term fix is to only fill the tank ~3/4 full. My long-term fix is to confess my DIY sins and repent with a proper reinstallation. Can you save me?

 

Buy part 999 707 115 40 O-ring (44 mm i.d. x 4 mm thick). It goes under the sender unit and seals the fuel tank.

 

That sounds suspiciously like the o-ring that came with the sending unit, and that's already installed. Should there be a second one on the outside? If not, I guess I'll double check my o-ring installation status; maybe it slipped or was misaligned all along.