The primary function of the fuel cap is to seal the fuel tank, preventing fuel from spilling and protecting it from contaminants such as dirt, dust, and water.

Many modern excavators, including Caterpillar models, have fuel systems designed to maintain a certain level of pressure. The fuel cap helps regulate this pressure, ensuring optimal fuel delivery to the engine.

The fuel cap is designed to prevent unauthorized access to the fuel tank, reducing the risk of theft or tampering. It also helps prevent fuel evaporation, which can be a safety hazard.

Some fuel caps are equipped with a venting mechanism that allows air to enter the tank as fuel is consumed. This prevents a vacuum from forming, which could impede fuel flow to the engine.