Without an infrared thermometer, how can I discern the proper temperature?
The oil should be cooking at less than a simmer. You will see the oil slowly vacillating around the cooking vessel and there will be a small amount of bubbles moving around the oil that rise to the top. Stir occasionally. Keep below a simmer. DO NOT BOIL! If it appears that the oil is about to go beyond a simmer and head toward a boil, simply turn down the heat and continue to keep a watchful eye over your cooktop. As a rule of thumb I suggest setting your cooktop to medium-low. All cooktops are different and they all exhibit different ballistics. You must spend some time with your kitchen equipment and get to know it. Remember, cooking is an art, not an exact science.