Importance of Oil Viscosity

first of all there is an operating temprature range for an oil where there is no or little change in viscosity..........

as viscosity decreases with increase in temprature the shear strength of oil reduces thats its importance in gear oil

Sorry abc - there will be change in viscosity of oil within the operating range too.

Though the amount of change (x45) for 50⁰C is a bit exaggeration (me think)

Usually as I remember, within operating range, every 20⁰C temperature rise the viscosity halves. So the 50⁰C drop (with the 220Cst at 40^oC) will cause only x5 to x6 viscosity ie around 1100 Cst and not the another zero.

The extra viscosity will have problem in oil circulation through the system and I am not sure about the design and lubrication system, but those who know have replied- the OEM)

What is your actual temperature of ambient range?

Also when the gearbox runs, in case of thicker oil, the losses make it quickly heat up and it warms up considerably, and it really doesn't matter if the gearbox is continuously running. However in lower duty gearboxes, the thick oil as mentioned above may create some problem in lubrication.

We normally put a small heater in the sump (along with heat tracers in case the line is long) to bring up the temperature to a comfortable zone before either the lubrication system (if it is external) or the gearbox is energised.

BTW: Please turn the caps lock off.