Vented Vs Non Vented Fuel Cap

Look at the front of tank at the axle for a u shaped metal vent tube about one inch in diameter.

Vented vs non vented fuel cap.

The vented gas cap has a one way release valve that is pressure activated. All modern vehicles use a non vented cap. 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. 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.

The non emissions caps freely vent the tank to the atmosphere which can waste gas through evaporation. If your tank has a vent then you will need a non vented cap. 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. When the pressure reaches a certain point defined by so many pounds per square inch the valve opens by a very small amount relieving some of the pressure.

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. Gasoline systems have been running non vented caps for quite a while due to the emissions requirements. Both styles of caps provide vacuum relief. Emissions gas caps have a built in pressure relief valve that will only vent to the atmosphere if the pressure gets too high.

Vented gas logs produce carbon monoxide emissions so your fireplace must have a chimney or flue. Vented caps only vent one way into the tank to allow air in as the fuel is used to prevent a vacuum from occurring. The vented gas cap is designed to vent small amounts of air into the car gas tank line.