Most fuel pumps in modern vehicles are submerged in the fuel tank. When the tank is nearly empty, the pump is drawing fuel from only a small area at the bottom of the tank. This can lead to several issues:
* Increased Heat: The fuel pump works constantly to draw fuel, and with less fuel surrounding it, it can overheat. Overheating can reduce its efficiency and ability to deliver fuel properly to the engine.
* Vapor Lock (though less likely in modern systems): In very hot conditions, with low fuel levels, the fuel can vaporize, creating vapor bubbles in the fuel line. These bubbles disrupt the flow of liquid fuel to the engine, making starting difficult. While modern fuel injection systems are designed to mitigate this, it can still contribute to a difficult start.
* Straining the Pump: Drawing fuel from the bottom of the tank can put more strain on the pump, potentially leading to weaker delivery, especially if there's any sediment or debris at the bottom.
When the tank is more than half full, the fuel pump is surrounded by a significant amount of fuel, keeping it cooler and allowing it to operate more efficiently and powerfully. The fuel is also readily available, minimizing the strain on the pump. This leads to a more consistent and robust fuel delivery to the engine for easier starting.
