► Choice of engine oil is based on the ambient temperature in the area, with considerations for your cooling system type.
• It's been in the 90°F+ range for the last 8 weeks here in Georgia, so I'm running 15W50 in my well broken-in, air-cooled V-twin mower. I'll go back to 10W30 when cooler autumn temps get here.
• If my mower was water-cooled, then the operating range of the oil would be controlled by the radiator's thermostat, not the heated air. So I'd be using 10W30 all year round.