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OM 617 – Viscofan coupling, temperature-controlled (engine 617)

The Viscofan coupling is a maintenance-free, hydraulic coupling which operates independent of temperature as well as infinitely variable.

When the engine is started (cold start), the fan will initially run at higher speed until the oil has flown back from the working chamber (75) into the reservoir (74) (approx. 1-3 minutes). The fan coupling will then switch off. The fan speed in disconnected condition depends on engine speed, but a fan speed of approx. 21OO/min should not be exceeded.

This condition remains in force as long as the engine maintains its normal operating temperature.
If the coolant temperature increases as the result of a higher load or higher outside temperatures, the air which flows through the radiator and actuates bimetallic strip will become warmer. The bimetallic strip (69) changes its shape under the increasing heat and opens at approx. 73 c a valve by means of a control pin (68) and thereby the path of the oil from the reservoir (74) into the working chamber (75) so that the fan will be additionally engaged.

During this control operation, the coolant temperature is between 90 and 95c.
With the clutch engaged, the fan speed in lower speed range will increase approximately proportional with the increasing engine speed, but will not exceed 35001 min in upper speed range.

Checking connected temperature
Run engine at 4000-4500lmin. When a coolant temperature of 90 to 95cis attained, the fan speed
should increase by approx. 1 OOOImin., which can be clearly noticed accoustically.

A defective coupling cannot be repaired with workshop equipment, and a new coupling should be installed.

Transportation and storage
Temperature-controlled Viscofan couplings should be transported and stored vertically. For short periods e.g. during assembly – the coupling may rest on a flange, but never on front end.


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