General maintenance of tractors and agricultural equipment will include an oil change and the question will arise as to which grade or type of oil to use in the engine. The answer to that varies with several factors, including the engine used, the fuel used in the engine, the operational hours of the engine, and most significantly, the ambient temperatures in which the tractor is to operate in.

Engine motor oil lubricants offer several functions in an engine, including lubrication, engine cooling, removal of impurities in the engine, a sealer of small microscopic holes in seals and gaskets, and as an inhibitor of corrosion by preventing rust from forming on the internal engine components. To perform these functions efficiently, appropriate oils must be chosen based on the engine application and the other functions mentioned above.

The first selection factor is the engine fuel itself. Diesel engines are manufactured to higher compression rations and will need better protection that gasoline engines. Thus, the oil chosen must be specially manufactured for gas or diesel engines.

The ambient temperature is one the most significant factors in oil selection.

For above zero Celsius (32 degrees Fahrenheit, the single (mono) grade SAE 40 oil can be used for temperatures between 10 degrees C (50 degrees F) to 50 degrees C (122 degrees F). The straight SAE 30 can be used between 0 degrees C (32 degrees F) to 40 degrees C (104 degrees F). The single grade SAE 10W winter motor oil can be used between -25 degrees C (-13 degrees F) to 10 degrees C (50 degrees F).

The multi grade oils have a large variation of temperature applications, with the largest variation oil being the SAE 0W-40 multi grade oil, which can be used in temperatures -40 degrees C (-40 degrees F) to 50 degrees C (122 degrees F). Like the SAE 0W-40, the SAE 15W-40 and SAE 10W-40 can both operate to a maximum of 50 degrees C (122 degrees F), however, the minimum temperature of the SAE 14W-40 is approximately -18 degrees C (-2 degrees F), and the SAE 10W-40 minimum is -25 degrees C (-13 degrees F).

The SAE 10W-30 has the same minimum temperature of the SAE 10W-40; however, a maximum ambient temperature of 40 degrees C (104 degrees F) can be reached with no negative effects.

The SAER 5W-30 has the same maximum as the SAE 10W-30, but is designed for a slightly lower temperature of -30 degrees C (-22 degrees F).

Machines operating in temperature below -40 degrees C (-40 degrees F) will need to use oil that’s typically called "Arctic Oil" which has been specifically manufactured for such low temperature applications.