How Often To Change Your Lawn Mower Oil — And The Easiest Way To Do It

A gas-powered, 4-stroke lawn mower engine, like a car engine, needs maintenance. If you own a car, you know the drill: You need to take it in for an oil change every few thousand miles. But you may not be able to measure the interval between oil changes in miles for your mower. Instead, it's common to measure it in hours of run time. As a rule of thumb, you should change the oil in a push mower after 50 hours, and if you have a riding mower, you should change the oil after 50 to 100 hours. 

That means if your lawn maintenance routine involves cutting the grass every week and spending about two hours doing it, you should only need to change the oil approximately once per season. If your lawn is much larger or you use it to maintain other lawns, you may need to increase frequency. One exception to the 50 to 100-hour rule is if you buy a new lawn mower. For new models, you should change the oil after 5 hours of run time, because the engine tends to shed small bits of metal and debris while it's breaking in. Complete the next oil change after 25 hours, and then all following ones after 50 hours (or 100 hours if you have a riding mower).

While 2-stroke engines aren't as common, it should be noted that this oil change schedule does not apply to them. Unlike 4-strokes, 2-strokes combine gas and oil in a single reserve, making oil changes unnecessary. 

Before you change the oil in your mower, run the engine for about 3 to 5 minutes. This warms up the oil and makes it drain faster and more completely. After shutting off the engine, disconnect the spark plug so the engine can't start unexpectedly. Now you're ready to drain the old oil; perhaps the most straightforward method, you can just unscrew the drain plug at the base of the crankcase, letting the oil flow into a container for disposal. 

If your lawn mower doesn't have a drain plug, an easy, clean way to drain it is with an oil siphon. These manual-operated pumps place one tube in the oil tank and another in a vessel. As you pump, the oil is suctioned from the mower tank and into a disposal container. Without a siphon, you can still tilt the mower on its side and let the oil flow out of the dipstick opening. However, this can get messy if you consider the risk of leaking gas and excess oil as you lean it. 

Before you add or buy new oil, check the owner's manual for the recommended oil grade and required amount for your mower. Pour the oil directly into the dipstick opening, using the dipstick to check the level frequently, taking care not to overfill the crankcase. When you're done, replace the dipstick and dispose of the old oil.