Q&A

 Master

Gas caps have not been vented since the introduction of evaporative emission controls/SMOG control on cars many years ago. All modern vehicles use 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. Your Catera should have a gas cap designed for that car. Stant and other aftermarket companies male them and are carried by most car parts stores.

A vehicle is equipped with a vented gas cap. Technician A says if a non-vented cap is installed in this vehicle, the gas tank could be collapse. Technician B says that if a non-vented cap is installed the vehicle could be starved for fuel at high speeds. Who is right?
answer: Both technician A and B are correct. The gas cap is an integral part of the design of the fuel and emission control system, and calibrated for the application. Internal fuel tank pressures can be affected by the use of an improper cap, or a cap that is faulty.
(Ref: this info is copy from a book).