Why should you never adjust the moldboard height when using a road grader?

Adjusting the moldboard height while operating a road grader is critical because it can significantly impact the machine's functionality and the quality of the grading work being performed. The correct choice focuses on the relationship between the heel of the moldboard and the main frame of the grader.

When the heel of the moldboard is under the main frame, this positioning can lead to the moldboard not functioning correctly. It can hinder the machine's ability to effectively cut and move material, resulting in poor grading performance. Maintaining the proper alignment and height of the moldboard ensures that it can operate efficiently and evenly, which is essential for achieving a smooth and level surface during grading operations.

While the other options mention potential issues related to moldboard weight, uneven grading, or increased fuel consumption, they do not directly address the specific operational mechanics involved. The emphasis on the heel being under the main frame captures a crucial aspect of grading dynamics that directly affects both the performance of the grader and the quality of the work being completed.