5W-30 Advantages
# A 5W-30 oil grade is useful in colder climates where temperatures are below 0 degrees Fahrenheit. It has a lower resistance at engine startup, allowing the engine to easily start in sub zero climates. These climates require that oil viscosity remain as thin as possible without giving up lubrication protection. Blaine Ballentine of Central Petroleum states that thinner oils exhibit less drag and wear on test engines run under normal conditions.

10W-30 Advantages
# A 10W-30 grade of oil is useful for year-round driving in moderate climates. Unlike 5W grades, an engine using 10W-30 oil can be operated at high speeds. This grade is specially formulated for modern engines which have tighter tolerances than engines prior to the 1980s. Tolerances are defined as an allowable amount of variation in the dimensions of a machine or part. Tighter tolerances have smaller degrees of variances. Blaine Ballentine argues that thicker oils, such as 10W-30, offer protection in severe driving conditions, such as driving on mountainous roads, towing trailers, in dusty conditions and at high RPMs. Thicker oil leaves a denser oil film coating on engine parts. Any abrasive contaminant which is equal to or larger than the oil film will cause engine wear. Thicker oil film can accommodate larger contaminants.