Engine oil does more than lubricating the engine. It performs the function of protecting from wear, removes contaminants from the engine, acid build-up prevention, protecting the turbos, etc. For this, factors like the mixture and the thickness/thinness of the oil play an important role. 

Usually, the engine oil needs replacement after every 5,000 - 15,000 kilometers. Or you can look for the following signs:

• Noisy engine
• The smell of the oil inside the car
• More smoke from the exhaust
• More fuel consumption
• Dark-colored oil

If the above signs are visible, it's time to replace the engine oil. But before choosing the oil, make sure that it is suitable for the engine of your vehicle.