How do you know when to change the oil and oil filter on your lawn tractor? Why should you care? The fact is the engine oil in your lawn tractor is critical to keeping it going. Not enough oil? You could ruin your engine. John Deere recommends you check your oil level before each use and to change your oil once a season. That’s about every 50 hours of lawn tractor use. Here are step-by-step instructions on how to change the oil and oil filter in your D100 Series Lawn Tractor. For specific information and more details check your Operator’s Manual.