4 stroke outboard engines need their oil changed. Unlike your old previous 2 stroke engines with an oil and petrol mixture, these newer 4 strokes need new oil at regular intervals. If you have a small outboard, say up to 4 horse power, then you should change the oil every 50 hours of running. For larger outboards you could go to 100 hours of running before changing the oil. If you don’t record how many hours your outboard has run, then change the oil at least once every year! New oil is needed by your outboard because the old oil degrades during engine use as it heats up and due to wear between the metals it collects metallic impurities and carbon from the combustion residue. Thats when it turns black! So change it and this will keep your outboard running longer and better efficient!