Why should an engine be rotated counterclockwise for a compression test?

Rotating an engine counterclockwise during a compression test is crucial primarily because it helps eliminate the compression release system that might be engaged in certain engines. Many engines are designed with a compression release mechanism to ease the starting process by reducing the pressure in the cylinder during cranking. By rotating the engine counterclockwise, you ensure that the compression release system does not inadvertently activate, allowing for an accurate reading of the cylinder's compression.

This process ensures that the compression gauge reflects the true compression level within the cylinders without the interference that a release mechanism could cause, leading to a misleadingly low reading. Accuracy in compression testing is vital for diagnosing engine health, as it directly impacts the assessment of valve sealing and piston ring condition.

The other options, while they mention elements associated with engine operation, do not address the specific need for correct orientation during a compression test.