The small engines that run lawn mowers need their oil changed just like car engines. Most mower engines need their oil changed every 20-50 hours of operation.
A mower's owner's manual will indicate how often to perform oil changes on the mower. At the very least, an oil change should be done annually with other seasonal tune-up maintenance.
This article explains the steps for changing oil in most mowers. Changing mower oil is very simple and can take as little as five minutes.
Step 1: Prepare for the Oil Change
1. Warm up the engine
Warming up the mower engine will speed up the oil change because the oil will flow more freely. It will also be a little easier to get all of the old oil out of the engine.
2. Clean around the oil fill area.
Use an air compressor or a clean towel to clean up around the oil fill area
3. Prepare an oil pan to catch the oil.
You'll need an oil pan or something similar to catch the oil from the mower. Position the pan on the side of the mower towards which you will tip it to drain the oil.