Answer to: oil changes on riding lawn mowersUnder normal residential use every 50 hours of operation. Drain oil when hot and be careful not to burn yourself with the hot oil. Add new approved oil slowly to the full mark on the dipstick or the bottom of the threads on the oil plug on an older engine. Always dispose of used oil properly. It contains nasty stuff. You can bring it to any place that does oil changes or the local Walmart. They will take it for free!