Depending on the tractor model, you can use SAE 20w-50 engine oil in the hydrostatic transmission. Other types of oil are also available, and their use can influence how frequently you need to replace the lubricant and filters. For better and more in-depth information, read the user's manual. Note: If your Husqvarna tractor has maintenance-free transmissions, it won't need routine oil changes unless mentioned in the owner's manual.