fuel tank question

[SteveO_71]

I plan on replacing my current tank and have been looking at new ones and I have a related question. One hole on top if for the fill pipe, the fuel sender is on the bottom but what is the other hole on the top? Do all 71's use that hole?

View attachment 29360

Thanks!

 

[Chris Womack]

Yes, all have it -- fuel tank vent hose. Here is a related link with additional information from this website.

http://www.7173mustangs.com/thread-73-gas-tank-fuel-vapor-separator

 

[72HCODE]

That is the fuel vapor vent, on top of the tank is a vent that connects via a soft hose then hardline through the transmission tunnel to the firewall. On the right side of the engine bay is the fuel charcoal canister. The canister then connects to air cleaner base. When the engine is running there is a slight negative pressure that feeds through the canister back to the fuel tank.

This sucks vapor and moisture out of the tank and prevents a full vaccum from forming inside the tank causing an implosion. The 71-73 cars uses a sealed gas cap for emmisions. If you didn't vent the tank then it would implode as the fuel was sucked out.

On your original tank top will be the vent, remember to transfer all hardware from the old tank to the new one as the vent is not reproduced. It uses the same rubber oring as the sender unit.