Fuel Filler Cap: Description and Operation

Fuel Tank Pressure/Vacuum Filler Cap:

PURPOSE
Provides slight pressure on the fuel reducing the evaporation rate and vacuum relief functions that allows the tank to vent.

OPERATION
Under normal operating conditions, the fill cap operates as a check valve preventing vapors from escaping the tank through the cap. Fuel system vacuum relief is provided after approximately -3.4 kPa (-0.5 psi) is reached inside the tank. Pressure relief is provided when pressure inside the tank builds up approximately 11.1-14.4 kPa (1.6-2.1 psi).

CONSTRUCTION
The threaded screw-on design cap incorporates an integral pressure-vacuum relief valve.

The fuel tank filler cap is a threaded screw-on with a pre-vent feature that allows the fuel tank to vent for the first three-quarter turn before unthreading.

The fuel tank filler cap is fitted with a torque-limiting ratchet to prevent difficulty in removal. When installing the fuel tank filler cap, continue to turn clockwise until ratchet mechanism gives off three or more loud clicks.

Fuel tank filler caps are attached to the vehicle with a tether using the fuel tank filler pipe-to-housing screw.