Diesel engines require their own type of fuel. Due to their high compression combustion, they use a diesel fuel oil. This fuel is available in three grades, depending on the temperature. Since oil gets thicker in cold weather, diesel fuel number one is used when temperatures drop below twenty degrees. For twenty degrees or higher, diesel fuel number two is used. And in temperate winter climates, a mixture of both called winterized number two is offered. Gasoline is rated by it's octane level. Likewise, diesel fuel is rated by cetane level. High cetane numbers allow for easier starts and smoother operating. Number one and two fuels have a cetane level rating of forty, however, most manufacturers recommend a rating of at least 45. Unlike gasoline octane ratings, diesel cetane ratings are not displayed as often or as prominently. It often requires visiting various diesel fuel stations to find fuel that produces the best results.