A fuel cap for an automobile is made of metal or plastic. It secures the entry to the fuel tank. Most fuel caps have threads, which are fixed to the tank pipe with matching threads. A rubber gasket at the top gets compressed when the cap is fixed and stops the leakage of fuel. The gas cap has air vents to allow the air to enter into the tank to maintain pressure. Generally, gas caps can be used as a closure for the fuel tank. On newer cars, the emission control has an engine light, which turns on when there is a leakage. If the seal is damaged or the cap cannot properly seal the tank, the lights will glow continuously. When you have problems you think might be associated with your fuel cap, try these troubleshooting tips.
Step 1 - Find the Problem
If you think your gas cap might be faulty, check that it is screwed on properly. Cleaning the cap and greasing the gasket may also help create a reliable seal. Next, check the gasket for excessive wear or find a replacement.
Step 2 - Find the Specs for the Replacement Gasket
Check your car manual to find specs for the fuel tank cap and its gasket and check with supply store to get the right type of cap gasket for your car. Select a suitable gas cap gasket. Do not try to substitute it with another type, even if it looks similar.
If cleaning or replacing the gasket doesn’t do the trick, there might be an issue with the cap itself. You may be able to repair your old cap. However, it will depend on the design and make of your vehicle.
Step 3 - Locate the Orientation Mark on the Cap
Find the orientation marks on the top of the cap. It is a white dot on the edge of the cap. Before disassembling the cap, mark on the bottom side of the cap using a marker that will be visible.
Step 4 - Remove the Bottom Part
Unroll the edge of the bottom part of the gas cap with a pair of needle nose pliers to separate it from the cap. The cap has three portions: the top, the middle, and the bottom.
Step 5 - Disassemble the Cap
Disassemble the gas cap parts. Make a sketch or take a few pictures before removing the parts and mark them for easy re-assembly. The inside portion will disassemble into numerous parts to reveal the valve and spring etc. There are O-rings also. These parts cannot be purchased separately.
Step 6 - Observe Any Dirt or Corrosion
Open the parts. You may find a lot of orange sticky fuel residues on the parts. Wash them with lacquer thinner to remove the residue.
Step 7 - Reassemble
Dry the parts after cleaning and washing. Reassemble the cap inside portion. Insert the top and the bottom portions. Keep pressure on the lower part when rolling its edge over the top to properly position the o-rings. Replace the gasket if it is cut, squeezed, or damaged.
Step 8 - Grease the Gasket
The gasket becomes hard with time. Many times, the old gasket can work by applying some lubricating grease on its face. However, it will work only for a short time. Put the cap on the fuel tank. If it still doesn’t work, you may have to purchase a factory-made gas cap or there could be a different problem with your emission system.