Gas cap issue

chope97

chope97

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I have a 71 2800 Bavaria i purchased a new cap a couple of years ago. This week I noticed when I take the cap loose a lot of pressure is released from the tank. Do I have the right cap? Are ther different caps for different years? Thanks for your help
 
chope97 said:
I have a 71 2800 Bavaria i purchased a new cap a couple of years ago. This week I noticed when I take the cap loose a lot of pressure is released from the tank. Do I have the right cap? Are ther different caps for different years? Thanks for your help
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there is no such a thing as a GAD cap

if you say pressure it might be the coolant reservoir cap, maybe you meant gas cap ? but there is NO pressure as the cap should be vented AND additionally the filling neck has a hose to vent the fuel reservoir naturally, very strange

any reservoir holding fuel will experience expansion with temperature changes, this is why it must be vented on high areas

did someone changed the neck ?


FYI, fuel presure in a CS after the pump will be 0,2 bar during normal fucntion, and after stoping engine will increase up to 0,4bar due to fuel thermal expansion and then slowly reduced back to zero
 
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@deQuincey , the OP meant "Gas" cap. I think.

@chope97 ; There is a tank vent on EU e9 models running a small rubber tube of the fuel filler neck, inside the trunk, around the tank to just behind the licenseplate where it exists through the floor with a plastic plug.

I'm not sure about E3 nor (later) US specific polution restrictions though.
 
eriknetherlands said:
@deQuincey , the OP meant "Gas" cap. I think.

@chope97 ; There is a tank vent on EU e9 models running a small rubber tube of the fuel filler neck, inside the trunk, around the tank to just behind the licenseplate where it exists through the floor with a plastic plug.

I'm not sure about E3 nor (later) US specific polution restrictions though.
Click to expand...

i mentioned it, there is a metal hose coming out the neck
but in nay case the cap should be vented

ps. i do have a vented extra cap that i can part with
 
For fuel tank venting....
This is the set-up the US cars have of your model....
There should be a small tube running from the fuel filler to the expansion tank and then off to the carbs up front (if memory is correct)

For non-USA cars... the vent out from the expansion tank does not go to the carbs, but just exits the tank and goes down through the trunk floor... See...

Most folks I know (from 2002 through to E3 and E9) run the Euro set up. As long as the tank is not plugged and the lines are open - should not have any pressure in the fuel tank to speak of....

Good luck....
 
lip277 said:
There should be a small tube running from the fuel filler to the expansion tank and then off to the carbs up front (if memory is correct)
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True dat...but first the line from the expansion tank goes to the charcoal canister under the battery tray then out of that to the base of the air cleaner.

I don't see any need for a vented gas cap with this set up. In fact, the fuel filler is so low that I would think. gas would dribble out of a vented cap with a full tank and under acceleration. In addition, a vented cap defeats the purpose of the factory closed ventilation system. I suspect your vent system (expansion tank, etc) is plugged. (BTW, the wooosh you hear may also be air ENTERING the fuel tank when you remove the cap. If this is the case, the fuel will not feed at some point with the vacuum created in the tank as fuel is consumed).
 
thanks for your reply, charcoal canister long gone. No line from there to weber carbs with small filters. Can I use another canister from a different car that may still work? I may have a canister on my parts car (74) but will it still work after all these years? I also have a 73, I noticed a line input on the bottom of the stock air filter housing is this for the fuel vapor input from the canister. My 73 has stock air cleaner but no connection to the canister. I need to check under the battery on that car to see if the canister is there. I am starting to smell gas vapor in the 71 so I will check the vapor line and rear plastic tank
 
The purpose of the canister is to hold gasoline vapors when the car is not running. When the car runs, a small amount of intake air is drawn through the canister pulling the stored vaports into the engine. The system is not closed and will not allow vacuum to build up in your gas tank because there is a connection from gas tank filler neck to the canister and from the canister to the air cleaner.

If your 71 has Webers with small filters, there is no easy way to duplicate the stock mechanism. Said another way, there is not much point in installing a charcoal canister without a mechanism to draw vapors through the canister and into the engine.

Its likely that someone plugged the line from the fuel tank to the canister when the canister was removed. This then seals the system and allows a vacuum to build up in the gas tank. That rush of air you heard was air entering the gas tank because of this vacuum. Best solution is probably to go with the European setup, which is a small hose from the gas tank filler neck thru the trunk floor (see Kevin's post above). This is what I've done with my car (with Weber carbs and a missing canister).
 
My US spec'd 70 2800CS never had a charcoal canister. I had a heated discussion about it during a smog check one time before it reached the California smog check 'not required' date for the 70 model cars. There is a line that comes from the plastic accumulator in the trunk that goes directly to the stock air breather. The rubber line got crimped one time and the gas tank did build up pressure. It didn't take me long to find the problem and get it fixed.
 
Dick Steinkamp said:
True dat...but first the line from the expansion tank goes to the charcoal canister under the battery tray then out of that to the base of the air cleaner.

I don't see any need for a vented gas cap with this set up. In fact, the fuel filler is so low that I would think. gas would dribble out of a vented cap with a full tank and under acceleration. In addition, a vented cap defeats the purpose of the factory closed ventilation system. I suspect your vent system (expansion tank, etc) is plugged. (BTW, the wooosh you hear may also be air ENTERING the fuel tank when you remove the cap. If this is the case, the fuel will not feed at some point with the vacuum created in the tank as fuel is consumed).
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given the configuration, that has a venting hose “a” and venting hole “b”

doubt much that you can have fuel dribble out of vented cap
Earlier venting hose could do

22027C93-5A29-4928-B0E5-4B326F53168F.jpeg
 
All E3s had non vented gas caps.

Luftdicht (airtight) is stamped on the inside of all original caps...

IMG_7412.jpg


All E3s had either the US vapor recovery system or the Europe vent system pictured by Kevin in post #5. Neither used a vented cap in addition to the tank venting system. If the venting system is blocked, a vented cap would be an alternative way to vent the tank as long as it does not dribble gas out the vent hole under acceleration or introduce fuel vapors into the trunk and/or cabin.
 
On a side note - many (most?) of the 2002's I am familiar with (at least for cars who have been worked on a bit that I saw from the mid 1980's through to today) have run the vent line straight from the fill tube down through the trunk to the outside. No other hardware. Not saying that that is what you should do - but that is common way to vent the tanks in cars that I have seen. I did that in my 2002. I was worried about smelling gas in my garage, but didn't. Now... my Mustang - that was a sniffer!!!! LOL
 
Dick Steinkamp said:
All E3s had non vented gas caps.

Luftdicht (airtight) is stamped on the inside of all original caps...

View attachment 187050

All E3s had either the US vapor recovery system or the Europe vent system pictured by Kevin in post #5. Neither used a vented cap in addition to the tank venting system. If the venting system is blocked, a vented cap would be an alternative way to vent the tank as long as it does not dribble gas out the vent hole under acceleration or introduce fuel vapors into the trunk and/or cabin.
Click to expand...

it is extremely difficult to say, and more difficult to believe, when someone says "all is/were..."
i would rather prefer to say "all the dogs that i know of are red"
it handles better the possible exceptions

said that, ehem, ....all the E3s and E9s that i have seen in my life have the vented cap and say "mit lüftung"

...maybe they were original,...maybe not
 
Hello,
alle european E9 must have a gas cap without venting (luftdicht, ohne Belüftung) because you would have gas fumes inside the trunk if the rubber booth behind the gas flap may not be airthight anymore (and you would use an not airtight gas cap). The venting of the E9 tank is done by a small tube running from the metal filler neck inside the car to a hole in the middle of the car/top of the trunk floor
European E3 must have a gas cap with venting (mit Belüftung) because the filler neck was not inside the trunk. The fuel tank was vented by the vented cap (mit Belüftung)
With help from the german E9 forum
Hope this helps Ulrich
 
I'm sure my Euro E3 has a label next to the cap stating that a vented (yellow ?) cap must be fitted (from memory). I'll take a photo when I'm back home.
 
my e9, has a beluftet cap, no fuel fumes in the car, nothing, no, nicht

1722689190911.png



i promise i will not start a religion,...
not saying this is correct, right, the thing to do

i say, this is in my car and it works

no fuel spills
 
Walloth sells unvented OEM BMW for our e9.

But it’s not specifically for e9..
 

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