Tractors use regular motor oil for engines or oil marketed by engine and equipment manufacturers for their products. The surrounding air temperature determines the viscosity and type of oil used in tractor engines, since they thicken in cooler environments and thin out in higher temperatures.
The Society of Automotive Engineers rates engine oil viscosity. SAE 30 petroleum motor oil is ideal for small engines in warmer climates, while a thinner mix or a multi-grade engine oil with dual viscosity of 10W-30 is ideal for colder regions. 10W defines the oil's viscosity at 0 degrees Fahrenheit, while 30 stands for the viscosity at the engine's operating temperatures.