Generators, including Onan generators, require a visual inspection for every eight to 10 hours of running time and additional maintenance at 100, 500 and 800 hours of running time. Maintenance schedules vary based on the type of generator used.
Oil and propane generators typically require replacing the air and fuel filters every 100 hours of running time, and the standard maintenance for diesel generators includes replacing the coolant, radiator cap and thermostat every one to two years. Gasoline generators are inspected annually to ensure the fuel lines aren't cracked or damaged. Most maintenance schedules include changing the oil and air filter after 100 to 150 hours of use, and the exhaust system, slip rings and brushes are inspected after 500 hours of use.