What Oil Weight to Use in a Riding Mower

Viscosity

• Oil viscosity is rated by a number that is determined by how well the oil operates at extreme temperatures. Oil weight is determined by the temperature in which you will operate your mower. The lower the number in front of the "W," the faster the oil flows on start-up in colder temperatures. That means that your engine spends less time operating without oil between the parts, thus reducing wear and tear. Multi-viscosity oils are able to work well at a higher temperature range because they are able to adjust their flow speed accordingly.

Outside Temperature

• Pick the oil weight based on the outside temperature in which you will operate your riding mower. Synthetic 5W-30 oil can be used for all temperature ranges. If you are operating the mower at 6 degrees and above, you need conventional 10W-30 oil. If operating when temperatures are 40 degrees and below, such as when using a snow plow attachment, use 5W-30 weight. If you plan to use your mower only in warmer temperatures of 46 degrees and above, use SAE 30.

Synthetic Oil

• It’s acceptable to use synthetic oil in your riding mower engine instead of conventional oil. Synthetic oil doesn’t burn up as quickly during use, so you won’t have to replace it as often during regular engine oil checks. Synthetic oil does cost considerably more -- up to three times as much -- but it’s also environmentally friendly. You can also leave synthetic oil in your mower longer during the off season. However, synthetic oil is not as good at coating your mower’s moving engine parts as conventional oil is.

Conventional Oil

• There are some challenges when using conventional oil in your mower. If your mower tips over and conventional oil enters the combustion chamber or exhaust area, it emits smoke that pollutes the ambient air. Conventional oil also burns up over time, which means that you will need to refill or change the oil more often than with synthetic oil. However, conventional oil is relatively inexpensive and adapts well to lubricating mower engine parts.