I know its an old thread. But to help others I am posting here.
Santro has got an ECT sensor Engine Coolant Temperature sensor having 4 wires connector which sends coolant temperature to speedometer gauge to show it on needle and also to the the ECU of car, the ECU reads this temperature and decides the fuel spray pattern, lean and rich fuel delivery, ignition timing and auto fan ON/OFF switching function, therefore ECT sensor is also called the MASTER SENSOR, its proper functioning ensures better fuel economy, smooth idling and efficient performance. The engine when first started in the morning while it is cold the ECT tells ECU that engine is cold so ECU keeps fan switched off, rich the air fuel mixture, signal the Idle control actuator to increase Idle, timing advance etc... Until the engine warms up. So NEVER EVER CONNECT FAN IN DIRECT MODE, And NEVER EVER COMPROMISE PROPER FUNCTIONING of the ECT sensor. Its really easy to check ECT sensor and its wiring at home. Just read santro manual or get info from internet. If ECT sensor is faulty and sending cold tempreture all the time then the fuel average will be worst as the ECU is pumping more petrol and FAN will not be switching ON so the engine will be OVERHEATING. For proper fuel efficient and improved petrol average ECT sensor accurate reading is very important. So try not to solve the overheating problems by desi jugarr methods because Your car ECU needs proper readings for efficient functionality.