Which of the following is NOT a cause for fan clutch replacement?

The correct answer is that a fan stopping within two seconds after shutdown is not a cause for fan clutch replacement. This phenomenon can be considered typical behavior for a thermal or viscous fan clutch, which is designed to disengage as the engine cooling requirement diminishes. When the engine is turned off, the fan may stop spinning rapidly due to the absence of the drive force provided by the engine, which can cause it to coast for a short time before coming to a stop. Therefore, a quick stop after shutdown is not indicative of a malfunction that would necessitate replacement.

In contrast, the other options identify behaviors or conditions that suggest potential issues with the fan clutch requiring inspection or replacement. For example, an oil film on the back of the clutch can indicate a leak that may impair its operation, while a lack of viscous drag means that the fan may not engage properly. Additionally, if the fan speed does not increase as the engine temperature rises, it suggests that the fan clutch is not functioning correctly and may need to be replaced. Each of these conditions directly points to a failure in the fan clutch's ability to regulate fan speed in response to engine temperature changes.