Dear Vin,

firstly: The water fill should have had a reason, as such choice of fluid often is done for environments under explosion hazards or fire hazards. So then, which was the reason for your plants layout decision to use water? There might be regulations to that!

secondly: In general, one of the base features why to take on a fluid coupling is the inherent overload protection, which you have lost due to higher (what exactly?) fluid viscosity (* see below). You may find that on the OEM's info or at least on the oil can the mechanics used when changing the fill. However, you may now be constantly overloading the motor and rising the overall stress level within your mechanical drive system (shafts, bearings etc.). This should be thoroughly assessed, if not beforehand, then at least now.

thirdly: Usually a fluid coupling possess a safety feature called the melting screw or some other device limiting the pressure / temperature of the fluid within the coupling and blowing off the overhot fluid / setting off an alarm to the control. You say: "change of media without change in the coupling". With such a major change as to use oil instead of water, please check the correct functionality of your couplings safety device.

Regards

R.

(* edit of 5.1.: However, the argument of Mr. Blenkhorn remains in my opinion valid. The torque transfer equation of fluid couplings says that torque is indirect proportional to the density of the fluid.) ■