The ideal is between 350-375ºF/176-190ºC. Too cold, you'll end up with a soggy, oil-laden mess. Too hot, and it may smoke and cause burned chicken on the outside and raw inside. If you don't have a thermometer, you can test the correct temperature by dipping the end of a wooden spoon or chopstick into the oil. When it starts to bubble around the wood steadily but not vigorously, the oil is ready.