At what temperature should the transmission level be checked?

The correct answer is checking the transmission level at operating temperature while running because this is the procedure most manufacturers recommend for accurately determining the proper transmission fluid level. When the transmission is at its operating temperature, the fluid expands, which can affect the level reading. A reading taken when the transmission is cold could lead to an inaccurate assessment, as the fluid would not have expanded to its operational volume.

Checking the transmission at operating temperature ensures that the fluid is in the same condition it would be during normal driving, allowing for a reliable measurement. This procedure helps ensure that there is neither an overfill nor underfill of the transmission fluid, both of which can lead to performance issues and potential damage to the transmission.

The options regarding cold checks, room temperature, and after cooling do not provide the necessary accuracy because they do not account for the fluid expansion that occurs when the system is running. Therefore, they are not typically used as standard practices for checking transmission fluid levels.