Using the correct type of oil is essential for maintaining the performance and longevity of a push mower engine. Push mowers are typically powered by small, air-cooled engines that require specific lubrication to handle high operating temperatures. Understanding these oil requirements is the first step in proper maintenance.
The Standard Oil for Most Mowers
Most push mowers use a four-stroke engine, which requires a separate oil reservoir in the crankcase for lubrication. For warm-weather operation, the traditional and most common oil specified by manufacturers is SAE 30 motor oil. This is a single-grade oil, meaning its viscosity is rated for a specific temperature range.
A common alternative is 10W-30 oil, a multi-grade formulation that offers a wider operating temperature range. Small engine oils are often formulated differently than automotive oils to account for the higher operating temperatures of air-cooled engines, frequently containing specialized additives. Always consult the owner’s manual for the correct oil type and API service category for your specific engine.
Matching Oil Viscosity to Temperature
The numbers on an oil label, such as SAE 30 or 10W-30, refer to the oil’s viscosity, which is its resistance to flow. Single-grade oils like SAE 30 are recommended when the ambient temperature is consistently above 40°F (4°C), as this oil maintains a stable viscosity at high summer temperatures.
Multi-grade oils, such as 10W-30, perform across a broader temperature spectrum. The “W” stands for “Winter,” and the first number (10W) indicates the oil’s viscosity when cold, allowing easier flow during cooler starts. The second number (30) indicates the viscosity at the engine’s operating temperature. Using 10W-30 is often recommended for year-round use or in fluctuating climates, providing better lubrication during cold starts.
The Two-Stroke Engine Exception
A small number of older or specialized push mowers use a two-stroke engine. These engines do not have a separate oil sump or crankcase. Instead, the oil must be mixed directly with the gasoline before it is added to the fuel tank.
Using the wrong oil or failing to mix it with the fuel will cause immediate engine failure. The required oil is a specific 2-stroke engine oil, often labeled with a TC or TC-W3 rating. It must be mixed at a precise fuel-to-oil ratio specified by the manufacturer. This oil-fuel mixture lubricates the engine’s internal components as it burns, ensuring proper function and preventing damage.
When and How to Perform an Oil Change
Maintaining the oil level and quality is important for the air-cooled engine’s health. The oil should be changed at least once per mowing season or every 50 hours of operation, whichever occurs first. For a brand-new engine, an initial oil change is recommended after the first five hours of use to remove metallic debris from the break-in period.
Before every use, check the oil level by removing the dipstick, wiping it clean, re-inserting it fully, and verifying the level against the “full” mark. To perform a change, run the engine briefly to warm the oil, which helps it drain more completely.
Turn the engine off and disconnect the spark plug wire for safety. The old oil can be drained by tipping the mower on its side with the spark plug facing up or by removing a drain plug. After refilling the engine with the correct new oil, the used oil must be taken to a recycling center for disposal.