Fuel filler cap

[mcknight77]

Vented or un-vented?

What should they be?

Jim

 

[blubuckaroo]

I believe all Broncos came with vent systems and sealed caps. You can eliminate the system and replace the caps with vented.

 

[mcknight77]

That's what I thought, Blu. But my system is pressurizing and blowing fuel out of the filler neck when I take my cap off.

 

[blubuckaroo]

Your vent system is either plugged up or capped off.

 

[Broncobowsher]

Early were vented caps.
Later were non-vented caps. Venting was done via the charcoal canister to capture the vapors and burn them in the engine.

 

[broncnaz]

Actually later model caps are considered to be the vented type as they allow air in only. So they have a one way vent. Nonvented caps allow air in and out. So really no vent at all.
If you dont have a charcoal canister setup then then the nonvented is supposed to be the one to use.
For many years I've used the vented type on my setup as I dont run the charcaol canister. About the only time I have issues is if I fill up the tank on a hot day and dont drive it enough to get the level down then it will leak out the cap but otherwise its fine.
Of course unless your having driveability issues the pressure in the tank shouldnt hurt just dont pull the cap off when the tank is fairly full.

 

[blubuckaroo]

Actually later model caps are considered to be the vented type as they allow air in only. So they have a one way vent. Nonvented caps allow air in and out. So really no vent at all.
If you dont have a charcoal canister setup then then the nonvented is supposed to be the one to use.
For many years I've used the vented type on my setup as I dont run the charcaol canister. About the only time I have issues is if I fill up the tank on a hot day and dont drive it enough to get the level down then it will leak out the cap but otherwise its fine.
Of course unless your having driveability issues the pressure in the tank shouldnt hurt just dont pull the cap off when the tank is fairly full.

Oh! Ok. That's why the check valve. Thanks!

 

[broncnaz]

Many of the newer caps are supposed to have pressure relief valves but I have no idea how much pressure it takes to go to relief. That is mostly incase of a wreck where the fuel tank gets smashed.

 

[Broncobowsher]

Many of the newer caps are supposed to have pressure relief valves but I have no idea how much pressure it takes to go to relief. That is mostly incase of a wreck where the fuel tank gets smashed.

As fast as stuff gets crunched in a crash, no fuel cap could ever vent fast enough. If the cap flew off and the filler neck had no restrictions it still could not vent fast enough.

Yes, the modern gas cap does have a pressure relief, but it is a stage 2 in case primary venting (through the charcoal canister) fails. Venting out the gas cap on new cars is a no-no. That is venting hydrocarbons into the air. not good.

 

[SDlivin]

Interestingly enough I have tried several of the 'venting' gas caps, and it appears they never actually do anything because every time I pop the cap off it releases pressure/vacuum.

 

[mcknight77]

I'll check the venting to the charcoal canister.

I'll also remember to burn a bit out of both tanks when I fill up.

Thanks for the help.

 

[broncnaz]

As fast as stuff gets crunched in a crash, no fuel cap could ever vent fast enough. If the cap flew off and the filler neck had no restrictions it still could not vent fast enough.

Yes, the modern gas cap does have a pressure relief, but it is a stage 2 in case primary venting (through the charcoal canister) fails. Venting out the gas cap on new cars is a no-no. That is venting hydrocarbons into the air. not good.

Well thats there claim dont know if it actually works or not. Id also have my doubts about it working fast enough. I think the concept is to try and relieve any pressure build up hopefully preventing actual fuel leakage which is more harmful that a little vapor.