Vented Vs Non Vented Fuel Cap

The vented gas cap has a one way release valve that is pressure activated.

Vented vs non vented fuel cap.

Vented caps only vent one way into the tank to allow air in as the fuel is used to prevent a vacuum from occurring. If your tank has a vent then you will need a non vented cap. Gas caps have not been vented since the introduction of evaporative emission controls smog control on cars many years ago. The non emissions caps freely vent the tank to the atmosphere which can waste gas through evaporation.

Both styles of caps provide vacuum relief. If that tube is not present then you need a vented gas cap. Look at the front of tank at the axle for a u shaped metal vent tube about one inch in diameter. Gasoline systems have been running non vented caps for quite a while due to the emissions requirements.

All modern vehicles use a non vented cap. Gas fireplaces come in two configurations. The vented gas cap is designed to vent small amounts of air into the car gas tank line. A non vented cap is just that no venting at all and will not let air in or out so unless you have an eec tank or other vent setup elsewhere you ll have some issues.

Using a non vented cap on a car from the 1960 s that required a vented cap can cause the car to run for a while until the fuel system draws a vacuum in the gas tank. In these systems the tank incorporates a third vent line that is routed to a cannister inside the engine compartment that is designed to capture and recycle gases formed in the fuel system. Ventless logs do not put off these emissions so no chimney or flue is needed and the heat is more likely to stay in your space.