The radiator cooling fan on J model coaches is designed to operate in two stages. From the time a cold engine is started until it reaches operating temperature, the clutch operates in "Slip" mode. In this stage, the fan blades turn, but at a slower speed than the engine. If the engine begins to run hotter than normal operating temperature, the clutch will shift into the second stage, or "Direct" mode. In this stage the fan clutch "locks" the hub and pulley together, causing the fan to operate faster (roughly the same speed as the engine). Listed below are the temperatures that shift the clutch to each stage:
|Engine Temp Rising||Slip to Direct||205°F (96°C)|
|Engine Temp Dropping||Direct to Slip||190°F (88°C)|
The clutch system is designed to operate in Slip mode about 85% of the time the coach is driven. This results in optimal fuel economy, and minimizes fan noise while the engine is operating. The temperature gauge on the dash will also display this variation in temperature. It is normal for the temperature gauge to continuously fluctuate between 180°F to 205°F.
Attached to the back of the clutch is an air line. Air pressure supplied through this line shifts the clutch to Direct mode. See Figure 1.
If you experience engine overheat problems and the clutch doesn't shift into Direct mode, the fan can be locked in the Direct mode to enable the coach to be driven to a service facility. This is accomplished by bolting the clutch pulley to the hub. Below is the procedure for doing this.
If you need further assistance, contact the MCI Customer Support Center at (800) 241-2947.
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