roller bearing start to get hot on summer

[181273]

I got an roller bearing on a hydro vertical generator, that is lubricated with oil, and refregerated into a exchanger oil/air, the air used for refrigeration is taken from the plant... that means that in summer the heat inside of the plant is highest than 40º C.... we are thinking into the use of a new exchange, but in this time water/oil, taking the water from the income of the turbine, cause in this way will use the pressure of the water to make force the water to go inside of exchanger... but I don´t know exactly how to calculate the heat to disipate into de exchanger... we use viscosity 100 on the oil, and we got about 50 litres on a temperature of 60ºC and this is the temperature we got on the oil for lubrication... and the bearing temperature trips... I´ll like to know the formulations to calculate the exchange and the heat to disipate.
thank for your attention and sorry for my english