Mercedes-Benz ML550 Gas cap won't click or tighten Inspection at your home or office.

Common reasons for this to happen:

There are four reasons why a gas cap won’t click or tighten:

• Damaged gas cap: A damaged gas cap is far and away the most common culprit for a gas cap that won’t click or tighten. Gas caps with damaged threading won’t be able to lock tightly into the gas tank. Sometimes you can see a crack or break in the gas cap, but often the damage is not visible. Certain makes and models have notoriously finicky gas caps, and some have even resulted in recalls.

• Damaged gas tank threading: The gas cap is part of a two-piece equation. There’s the gas cap, with the outward threading, and the top of the gas tank, with the track for the threading. If this track for the threading becomes damaged, the threading has nowhere to lock into, and the gas cap won’t click or tighten.

• Dirty cap or tank: Everyone has accidentally tried to screw on the lid to a jar when something was caught in the threading. It simply won’t work. A gas cap is no different; if there’s debris in the threading of the gas cap, or in the track of the tank, the cap won’t screw on correctly.

• Broken spring load: Many gas caps are spring loaded. These gas caps rely on a spring that holds the cap in place when it is locked in. If this spring breaks or is damaged in any way, there will be no pressure holding the cap in place.