Mysterious O'Ring in Gas Tank

[John B.]

The title pretty much says it all. I pulled the tank out of my 535i yesterday to fix some rust issues. Removed the pump cover with float & pump attached & drained the tank. Laying next to the plastic pump housing mounted to the tank floor I found an olive green o"ring that measures about 26mm id/33mm od. Nothing like this shows up in the parts fiche & I can't see anywhere it would fit. Any ideas??

[John B.]

Looks like I've stumped the panel as they used to say on the old quiz shows. Good, now I won't worry about it. Tank is degreased & fume free so I'll sandblast it tomorrow. After making a few repairs I'm going to etch the bare metal & seal the outside with a couple coats of Mastercoat Rust Sealer Chassis Paints, Rust Paints & Chemical Resistant Floor Coatings (http://www.masterseriescoatings.com/index/) . This stuff hardens up like rock & can also be used to seal the inside of the tank. Mine's still clean inside after 23 years so I'll leave it alone.

[genphreak]

It's a plastic tank, right?

The o-ring sounds a similar size for the pump-pickup pipe on some pumps (but I've never seen one have an o-ring there myself). Sounds more like an AC pipe o-ring tho...

I certainly wouldn't worry about it too much.

[John B.]

If it was plastic I wouldn't be sandblasting it & repairing rust damage. Our old 95 525iT tank was also metal. Which models had plastic tanks?

[genphreak]

Doh! You did say that... lol

My '95 euro touring has a plastic tank and batter under the back seat (where's yours?).

In Aus we get mostly euro production as ours are all RHD. Most of the euro e34s I've seen have plastic tanks (from '87-'95). I've an '90 525i M50B25 (RHD from Japan) that has a steel one though- it has the battery under the hood to balance the extra weight (I think).

[ScottyWM]

On my old '93 E34, there was an o-ring about that size that would occasionally become displaced from the gas filler area. It was right below the small metal 'flap' that you stick the gas pump nozzle down into. When I would remove the nozzle, it would sometimes get caught in the flap. It seemed (in my mind) to be a seal for that flap. A long screwdriver would reposition it. I think I might have even posted here about it with a picture many years ago.

[John B.]

My '95 euro touring has a plastic tank and batter under the back seat (where's yours?).

Battery is under the passenger side of the rear seat but the gas tank sits under the trunk floor. Can you actually access the gas tank by lifting up the rear seat cushion???

[John B.]

On my old '93 E34, there was an o-ring about that size that would occasionally become displaced from the gas filler area. It was right below the small metal 'flap' that you stick the gas pump nozzle down into.

I believe we may have a winner! Looks like it would fit under the flange & be held in place by the spring loaded flap. It also looks like it would fall into the tank the first time I filled up so I think I'll leave it out as the flap seals tightly as it is.

[genphreak]

I believe we may have a winner! Looks like it would fit under the flange & be held in place by the spring loaded flap. It also looks like it would fall into the tank the first time I filled up so I think I'll leave it out as the flap seals tightly as it is. On ya ScottyWM!

I'll have to find one of those o-rings on a car that has it, never seen one before.

The flap and ring is fitted to unleaded cars in some markets only, and is either there to prevent fuel slopping up the spout under pressure when cornering, or to ensure positive gas pressure is routed through the engine emissions recirculation system. I left my cap loose once on a car without the unleaded fuel filler (Japanese production unleaded M50), and it proved the fuel sure slops out without it :-)

Maybe they all end up in the tank or ripped out- will have to see...

[Bill R.]

Hi John,
I'm sure that that is it also. On my 535 the inside of the tank had gotten rusted from sitting with a half tank of 10% ethanol gas in it for about 9 months or longer... It was easier and cheaper for me to get a replacement tank from a local junkyard and it was spotless inside, i think i paid 35 without the pump and sending unit

[John B.]

My tank was nice & clean on the inside after running nothing but E10 since 2004. Several of the vent connections up behind the rear wheel had rusted off & the tank rusted through right below where the vent hose attaches on top. All cleaned up with new fittings brazed on, the hole closed up & several coats of that Mastercraft rust sealer so it shouldn't happen again. Had it out today for a nice drive!