If you don’t have a thermometer, here are a couple of tricks for determining when your oil is hot enough to fry in. jfood describes the old-time method of dipping the handle of a wooden spoon or a wooden chopstick into the oil, and several hounds confirm that this does indeed work. When the oil is hot enough, it will bubble rapidly around the wood.
And Channa shares this simple method for checking oil temperature: Put a popcorn kernel in the oil as it heats. The popcorn will pop when the oil is between 350°F and 365°F, the perfect temperature for deep frying.
Board Link: Testing if oil is hot enough