Engine oil is translucent with a light tint. Over time, it gets darker and thicker. So, to check if it is time for you to get an oil change, you can do a basic dipstick test. The darker the dipstick is, the closer you are to your next oil change schedule. And if the dipstick is black, then it is time for you to change the oil. If the oil has turned brown or milky, then that is a bad sign. Usually, this happens when the coolant leaks into the crankcase of the engine. You can also use the smell of the engine oil to check how many more miles you have before the oil changes.