Where is the sensor for regulating the temperature R

There is no electronic coolant temp regulator. That is what the thermostat is for as it regulates the flow of coolant between the engine and radiator by opening and closing based on coolant temp. It is mechanical in operation and operates independently of everything else. If it is faulty and is stuck closed or partly closed you will get an overheat condition.

If you still have an overheating problem after what has been done then it could be due to one of these factors if all else is ok...

1. Air remaining in the cooling system retarding coolant flow. It is imperative that all air is bled from the cooling system or you will get an overheat condition cause by air blocks. If you still see bubbles appearing in the coolant this is an indication that there is still air in the system or you may have the issue described in 3. Manufacturer procedures need to be followed for effective air bleeding of the cooling system after radiator coolant has been changed.

2. A partial blockage in the radiator or in the engine retarding coolant flow due to a build up of debris.

3. Combustion gasses leaking into the cooling system via a failed head gasket will cause an overheat condition. This will show up as bubbles in the coolant when the engine is running and can be checked by doing a leak down test on each cylinder. You might also have some coolant escaping into the cylinders and white exhaust emissions can be an indication of this. If you have been running the engine in an overheated condition this can very easily cause a head gasket to fail and a cylinder head to warp or even crack.