Gas cap hiss?

[chris norman]

hi, I've just fitted a chrome gas cap to my '74 360 duster and have since noticed a big hiss when the gas cap is opened which wasn't there before! I refitted the old one for a trip out and checked when home and there was no hiss? I believe both caps are vented as that's what was ordered! Should there be vacuum/pressure there?

 

[67Dart273]

NO Mopar cap is "vented" in the normal sense. Up through some of '70, the tank was vented and the cap was sealed.

As Mopar (the feds) implimented the carbon canister venting, these caps changed, but they all were known as "pressure relief." If the tank builds either suction or pressure, the cap releases the pressure. The tank VENTS through the carbon canister system. Go to MyMopar and download a service manual for free, it will tell you in a combination of the fuel section and the emissions section how that venting works

Here is a diagram from one of my old posts on this

 

[chris norman]

Ok thanks, I don't see any canisters or such fitted to my car so maybe changed about over the years, but it didn't do it on the old cap so any have to just put that one back on

 

[diymirage]

why did you replace it?

if its just looks, you can swap the outsides and use the old internals with the new chrome and see what it does

 

[67Dart273]

Ok thanks, I don't see any canisters or such fitted to my car so maybe changed about over the years, but it didn't do it on the old cap so any have to just put that one back on

If the system was removed, I would MAKE ABSOLUTELY CERTAIN that your tank is actually vented. With that system removed, the old 1/4" line coming up front MUST be "up high" and "open" in the engine bay. You can plumb it into the air filter bonnet, but it must be "open" to flow.

 

[Treblig]

There's a snake in your tank???????LOL


SORRY>>>>
Treblig