Can anyone identify this?

[Wishno87]

I found this on the passenger side rear fender-well by the gas filler. Its an 86. Does anyone know what this is? Seems to have something to do with the gas tank but not sure.

[mikeedler]

its the vapor/ expansion tank.

[Wishno87]

So fuel overflows into this?

[Jean]

Fuel vapor/gas.

[techterr]

Yes, fuel will overflow into this.. especially if you over fill the gas tank. It's main purpose was to collect fumes from the gas tank and filler pipe when the car was parked, so they wouldn't be released into the atmosphere... epa stuff, then the charcol canister in your engine compartment would suck up the fumes, then when you had started the engine, the little vacum valve valve under your throttle body would open and this would suck the fumes out of the charcol canister and burn them... If your vacum hose going to the charcol canister is off, or the valve isn't working correctly, that expansion tank can fill up.. Usually it's just from people topping off there tank too much.. Here is a diagram on real oem

http://www.realoem.com/bmw/showparts.do?model=1254&mospid=47308&btnr=16_0107&hg=16&fg=10

[Wishno87]

Cool thanks for the explanation.

[Van Westervelt]

Nooooob. ;) Just joshin ya Joshy.

[txtorquemade]

Anyone ever really change these out? The charcol filter I mean.

[e30devo]

Anyone ever really change these out? The charcol filter I mean.

its not a filter. it just absorbes fumes for emissions reasons, but when the car is running a correctly operating system should vent those fumes into the intake stream to be burned with the air/fuel mixture. usually the valve only opens at cruise speeds as to not effect drivability.