Which fuel line should you open when bleeding and priming a diesel fuel system?

When bleeding and priming a diesel fuel system, it is important to open the fuel line at the highest point. This is because air tends to rise to the top of a system, and by opening the highest point, you allow any trapped air to escape more easily. This ensures that the fuel can flow freely without any air pockets, which can cause starting problems or affect the performance of the diesel engine.

Opening the line at the highest point assists in ensuring that all air is purged from the system, allowing for efficient and reliable operation. Other considerations, such as the accessibility or length of the fuel line, do not directly affect the ability to effectively bleed the system of air. Therefore, focusing on the positioning of the line is crucial for achieving proper fuel flow and maintaining engine functionality.