The type of oil a generator uses varies by manufacturer and model, but Kohler recommends Mobil 1 5W30 synthetic oil for its generators. Generac recommends using SAE 30 at temperatures above 40 degrees Fahrenheit, 10W30 at temperatures between 10 and 40 degrees Fahrenheit and synthetic oil at lower temperatures.
In order to determine the correct oil for his particular unit, the owner should check the operating manual the supplier provides with the system. Before starting the generator, the owner should always check the oil level, and fill until it reads full on the dipstick. For generators that do not have dipsticks, the owner removes the cap and adds oil unit it just begins to drip onto the ground.