Vented fuel cap

[Mark B]

Hi All,
Does anyone know where I can buy a vented fuel cap for a 70 Challenger please? I filled up a week ago, pressure must have built up in the tank and it’s leaked out and damaged the paint and stripe below. Having to get the paint sorted now.
Thanks,
Mark.
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[RobTwin]

Ouch! That's a bummer
It's a right pain on our b-bods having the cap low down behind the licence plate, with the filler neck almost horizontal as fuel often spills out when filling up and can easily leak out when full if the seal in the cap isn't great, but at least it just spills out onto the ground without damaging any of the shiny stuff

[Matt]

Not so fast !

If your car left the factory with an unvented cap (which I think it probably did ? ) , it was for a good reason.

Check rubber sealing ring under cap is in good condition.

Check fuel tank and filler neck vent lines first for blockages ?


Neck vent here should release any excess fuel / pressure as long as
a) it's not blocked
b) the cap seals properly

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I've just been repairing one of my unvented B-body gas caps this morning with a sheet of nitrile rubber off ebay. I must have stolen the original seal off the cap years ago to use on something else.

Rubber thickness I used was 2mm and it squeezed nicely into the gap in the riveted assembly, using lubricant. A centre hole of about 22mm is good. I'll have to check if the cap seats properly now, but it's looking promising.

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Cheers

Matt

[Matt]

Original style unvented gas caps are available from RockAuto, as are locking ones (which are allegedly vented).

[Mark B]

Thanks for the information. The rubber seal around the cap is in good condition so the vent must be blocked.

I found this on the subject on E bodies forum.
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[Matt]

Ooh .

I may do some more research as ‘why does it work this way’ stuff like this interests me.

Is yours a flip-top gas cap, out of interest ?

[Mark B]

The outside cap is a flip top and the inside is the standard twist and open.

I’ve bought a new none vented inner filler cap see if it’s the seal.

[kma176]

I've been having an Email conversation with Stant about my 71'Satellitte they tell me mine should be vented and pressure relief ?? The new one I have was vented but not pressure relief but was the correct part number that should be !! As a temp measure I've removed the valve from the cap so it breathes both ways - I filled the tank to the brim today, drove 20 miles no pressure build up and no leakage !

[Mark B]

Interesting. Was there a strong smell of fuel in the garage after the drive?

[kma176]

No smell at all since removing the valve - I also blocked off the breathers as the Vapour tank had sprung a leak after pressurising pretty high and wasn't being used correctly anyway.
Mine had 4x breather tubes from the tank (one for each corner)they went to the vapour tank then a 5th one went from the Vapour tank to the engine crankcase breather system I think via a charcoal filter.They seem to have changed the design of this system a lot around this time also depending on which State !
I removed the valve from my cap rather than drilling a hole in it as the fuel still would have more of a journey to spill out of the cap !

All that said I'm still not sure how your breather system should work!!!