Description: The gas cap consists of a
plastic body with either threads (older caps) or lugs that locates
into the filler neck of the fuel tank. Quality caps incorporate
finely calibrated springs and valves. Caps may come in standard or
locking types that minimize the chances of tampering with the fuel
tank.
Purpose: The gas cap used to simply
cover the opening of the fuel tank filler neck, but eventually
strong safety and emissions initiatives pushed cap designs to
accomplish other tasks. The gas cap is now a major safety component
that prevents the flow of fuel back out of the tank filler when a
car is in an accident, including rollovers. This helps to reduce the
chances of fuel leaks and their associated dangers. The gas cap is
also an integral part of the onboard diagnostics system
(OBDII) and emissions control system, which are interrelated. The cap prevents the leakage
of fuel vapors from the filler neck, which can
be a major source of hydrocarbon emissions. A leaking or missing gas cap can result in the release of 30 gallons of fuel per year into the atmosphere.
Maintenance Tips/Suggestions: Always make sure your car's gas cap is
reinstalled properly after each fill-up. If you lose the cap,
replace it immediately for safety and emissions reasons. A loose gas
cap can cause your car's SERVICE ENGINE SOON or CHECK ENGINE light
to come on. If you find the cap loose, turn it to the right until it
"snaps". It may take several start-and-run cycles for the light to
reset. In areas with an emissions testing program, the gas cap may
be tested for its ability to hold pressure. If the
cap fails, it will need to be replaced. When you replace
your car's gas cap, make sure it's made by a reliable
manufacturer and that it's the right cap for that specific make
and model. Beware of "one size fits
all" caps and low-quality alternatives that may jeopardize your safety
and your car's emissions control system.
