You might find these articles linked below by Keith Calver, on Mini coolant and oil temperature of interest.
"Maximum power is usually generated from A-series engines at 70 – 75 degrees C (160 to 170 degrees F). The main problem with this on a road car is the oil is unlikely to get hot enough for maximum performance – the results outlined previously. Another being that the heater (where needed) will be grossly inefficient. So, excluding race-cars, the optimum temperature to aim for is 85 to 90 degrees C (185 to 194 degrees F)."
Cooling - Controlling coolant temperature:-
"Optimum performance, for both economy and power, is achieved at temperatures around 100-107 degrees C (210-225 degrees F). Up to 120 degrees C (250 degrees F) is OK if a decent oil is used, but getting a little warm. Some engine builders believe oil should be kept around 80 degrees C (175 degrees F) to keep things ‘safe’. This simply is not high enough for best performance. The biggest problem is actually measuring the running temperature in a Mini. You need to assess the mean oil temperature measured in the gearbox (sump temperature). Extremely difficult to do considering there’s no ‘natural’ position to mount the sensor."
Lubrication - Temperature critical:-
Edited by mab01uk, 18 May 2020 - 01:18 PM.