Here is a necessary rule to abide by when using oil in a frying pan or wok. Cold oil, cold pan. You see if you put cold oil into a hot pan… you will never know how hot the pan is or when the oil is ready to cook. Your pan may be so hot that your oil smokes immediately.
But, if you put cold oil into a cold pan… then turn on your heat, add a few bits of whatever you are cooking (garlic, onions, etc.) and then, when it starts to make noise and sizzle… The oil is ready!
This way it never gets too hot or reaches and unhealthy smoking point. If your oil does smoke, it can make your food taste off-putting. The smoking point marks the beginning of both flavor and nutritional degradation. So try it next time you are making a stir-fry… cold oil, cold pan!