Save a Tank of Gas

Save a Tank of Gas Per Year

If you live in a state that has regular emission control testing, you may have noticed that part of the test procedure includes an inspection of the fuel cap for leaks. While this may seem a bit trivial, a leaking or missing fuel cap can allow up to 22 gallons of gasoline per year to evaporate into the atmosphere. This hits you in your wallet as well as in your lungs through the air you breathe. Everyone knows that gas isn’t getting any cheaper and that 22 gallons of unburned hydrocarbons per leaking fuel cap contribute greatly to our air pollution problem.


The Clean Air Act of 1990 mandates emissions testing in certain states and metropolitan areas that don’t comply with minimum clean air standards. The penalty for not complying with these standards is a loss of government funds for highway construction and maintenance. Part of the emissions test procedure is to check the fuel cap for leaks. In states where mandatory emissions tests are required, you can’t drive without a properly functioning fuel cap. If during the emissions test your fuel cap fails, you are required to purchase a replacement cap, then have your car re-tested. This not only wastes fuel, but also wastes your time searching out a replacement cap and getting back in line for re-testing.


Historically while automotive exhaust emissions has been the focal point of government emissions regulations, the fuel cap has, up until recently, been largely ignored.


In 1970, California passed legislation mandating that all light duty vehicles sold in the state be equipped with evaporative emission control systems. These systems included special fuel caps with two-way valves, a pressure valve to keep gasoline vapors in the fuel tank, and a vacuum valve to allow air into the tank as it emptied. This regulation was adopted nation-wide in 1971.


This method of controlling fuel vapors at the cap remained essentially unchanged until 1996 when a new level of government regulations took effect. These new standards resulted in emission control limits 50 times more stringent than those of the past. New on-board computers in automobiles are now checking the entire fuel system periodically for leaks. If one is discovered, the "Service Engine" or yellow MIL light will illuminate. The car owner has no choice but to take the car back to the dealer for repairs. Often times the solution is to simply to turn off the light and correctly install or replace the damaged or leaking fuel cap.


New emissions standards have also resulted in new fuel cap designs. Since the mid 70’s the plastic threaded fuel cap was the standard type of cap for most light duty vehicles. The emission related problem with this design was that it could be "partially" installed by the consumer. That is, many times the cap was threaded into the neck but not fully ratcheted to the proper torque as required to create a proper seal. This partial installation can create a leak path triggering the "service engine" light. New "quick-on" design caps have reduced this problem. These new caps snap-on after insertion in the neck. The consumer cannot install the cap half way. It is either on all the way or not installed at all. Ford, GM and Daimler Chrysler have each adopted their own quick-on type fuel cap designs.


So it does not matter whether your car is new or old or if your car is equipped with an on-board computer. If you want to do your part for cleaner air and save money, replace and correctly install your fuel cap. Then we can all breathe a little easier.

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