Thermostat valve helps engine to quickly attain the optimum working temperature during cold starts. That is after cold starts, this valve restricts the flow of water inside the engine that makes it quickly attain the optimum temperature.
In winters, the valve will obviously open late since engine will need more time to attain certain temperature while in summer, the valve will open quick. Although removal in summer wont harm the engine that much, usually mechanics remove it, which in any case is not good for the engine.
Regarding the fan speed, it seems that the mechanic has either introduced a relay for the fan, or just bypassed the in-built resistance that allow the fan to revolve in 2 stages- low speed and high speed. Better remove any alterations made to the fan and use only desired fuse location somewhere near to battery, if required.
Before turning the automatic mode 'ON', get the Coolant Temperature Sensor analysed for any problem and replace if necessary.