Change your lawn mower's oil every 50 to 100 hours of use, or at least once a year

Most lawn mower engines need an oil change roughly every 50 to 100 hours of running time — that's typically once a season for a homeowner who mows weekly. Some mowers with smaller engines may need it more often; check your owner's manual for the exact interval. Dirty oil thickens, loses its ability to protect moving parts, and can cause the engine to overheat or seize.

The job takes about 15 minutes and requires only a few tools you likely already have: a wrench or socket that fits your drain plug, an oil filter wrench if your mower has a cartridge filter, a pan to catch old oil, and fresh oil in the grade your manual specifies. You do not need to be mechanically skilled — this is one of the easiest maintenance tasks a homeowner can do.

Key Takeaways

  • Run the engine for a few minutes before draining so the oil flows more easily, then turn it off and let it cool just enough to touch safely.
  • Locate the drain plug underneath the mower deck, position a pan beneath it, and unscrew it by hand or with a wrench to let old oil drain completely.
  • If your mower has an oil filter, unscrew it by hand, wipe the rubber gasket area on the engine clean, and hand-tighten a new filter until the gasket just touches, then turn it three-quarters of a turn more.
  • Refill with the exact oil type and amount listed in your owner's manual — overfilling or using the wrong grade will damage the engine.
  • Dispose of old oil at a recycling center, auto parts store, or municipal hazardous waste facility; never pour it down a drain or into the ground.

Warm the engine and locate the drain plug

Start the mower and let it run for two to three minutes. Warm oil flows faster and drains more completely than cold oil, which means less sludge stays behind in the engine. Turn off the engine and wait a minute or two — the oil will still be warm enough to flow freely, but cool enough that you can safely touch the mower without burning yourself.

Tip the mower on its side to access the underside of the deck. Check your manual first to see which side is safe; some mowers have the carburetor on one side, and tipping the wrong way can spill fuel into the engine. The drain plug is a bolt or nut on the lowest point of the engine block, usually with a washer underneath it. Position your drain pan directly below it before you loosen anything.

Drain the old oil completely

Use a wrench or socket to unscrew the drain plug, or simply turn it by hand if it is loose enough. Once it is free, carefully unscrew it the rest of the way and set it aside — do not drop it into the pan. Tilt the mower slightly if needed to help the oil flow toward the opening.

Let the oil drain for at least five minutes. You will see it slow to a drip, then stop. This is normal; small amounts of oil always remain in the engine. Once draining has slowed to nearly nothing, wipe the drain plug clean with a rag and set it aside. If the plug has a crush washer (a flat metal ring), replace it with a new one before reinstalling — a used washer will not seal properly and may leak.

Replace the oil filter if your mower has one

Not all lawn mowers have replaceable oil filters. Check your manual or look at the engine — if you see a cylindrical cartridge screwed onto the side or top of the engine block, your mower has a filter that needs changing. If you see only a spin-on filter (a can-shaped part), you will replace that. If you see neither, your mower uses an internal filter element that does not need regular replacement.

For a spin-on filter, use an oil filter wrench to unscrew it counterclockwise. Position your drain pan underneath because a little oil will spill. Once it is loose, unscrew it by hand and set it aside. Wipe the rubber gasket area on the engine block clean with a rag to remove any old oil or debris.

Take your new filter and apply a thin coat of fresh oil to the rubber gasket on top — this helps it seal properly and makes removal easier next time. Screw the new filter on by hand until the gasket just touches the engine, then turn it an additional three-quarters of a turn. Do not use a wrench; hand-tight is correct. Over-tightening will damage the gasket and cause leaks.

Refill with the correct oil type and amount

Open your owner's manual and find the oil specification — it will list a grade like SAE 30, 10W-30, or 5W-20, and the capacity in ounces or quarts. Using the wrong grade can damage the engine; thinner oil will not protect moving parts in hot weather, and thicker oil will not flow properly in cold weather. Buy oil labeled for small engines or lawn mowers, not automotive oil, unless your manual specifically allows it.

Remove the oil filler cap on top of the engine and set it aside. Pour in the oil slowly, stopping halfway through to check the level with the dipstick. Wipe the dipstick clean, reinsert it fully, then pull it out again to read the level. The oil should reach the full mark. Add more if needed, a little at a time, until it reaches full. Do not overfill — excess oil will foam, lose its cooling ability, and can damage seals.

Reinstall the filler cap and tighten it by hand. Wipe up any spilled oil with a rag. Set the mower back on all four wheels and let it sit for a minute before starting.

Run the engine and check for leaks

Start the mower and let it idle for a minute. Watch underneath for any oil dripping from the drain plug or filter. If you see a steady drip, turn off the engine immediately and tighten the drain plug or filter slightly. A few drops are normal as the new oil settles; a stream means something is not sealed.

Turn off the engine and wait two minutes for the oil to settle. Check the level one more time with the dipstick to make sure it is still at full. If it has dropped, add a small amount more. This is your baseline for future checks — you can now use this dipstick reading to monitor oil level between changes.

Dispose of old oil safely

Never pour old oil down a drain, into the ground, or into a storm sewer. Oil contaminates groundwater and harms aquatic life. Most auto parts stores that sell oil will take used oil for free, no questions asked. Municipal hazardous waste facilities also accept it, usually at no cost. Some recycling centers have dedicated oil collection bins.

Pour your used oil into a clean container with a tight lid — an old oil jug works perfectly — and transport it to your chosen disposal location. Keep it sealed during transport to prevent spills. Many places will also take used oil filters if you drain them first by letting them sit upside down in your drain pan for a few hours.

Frequently Asked Questions

How do I know if my mower needs an oil change?

Check the dipstick — if the oil level is low, top it off. If the oil on the dipstick looks black or very dark brown instead of amber or light brown, it is time for a change. Also check your manual for the recommended interval; most mowers need a change every 50 to 100 hours of use or once per season, whichever comes first.

Can I use automotive oil in my lawn mower?

Some mowers allow it, but most manufacturers recommend oil labeled for small engines. Small engine oil is formulated to handle the higher temperatures and speeds of mower engines. Check your manual before substituting. If it does not explicitly allow automotive oil, use small engine oil to avoid voiding your warranty.

What if I spill oil on the grass or driveway?

Soak up fresh spills immediately with rags or paper towels. For larger spills, spread cat litter or sand over the area to absorb the oil, let it sit for a few hours, then sweep it up. Do not hose it down — that spreads the oil and sends it into storm drains. Dispose of contaminated materials as hazardous waste.

Do I need to change the oil filter every time I change the oil?

Most manufacturers recommend changing the filter every other oil change, or at least once per season. Check your manual for the specific interval. If you are changing oil every 50 hours, you might change the filter every 100 hours. Some owners change both at the same time for simplicity.

Why is my mower leaking oil after an oil change?

The most common cause is an over-tightened drain plug or filter. If the drain plug is leaking, loosen it slightly — it should be snug but not cranked down hard. If the filter is leaking, loosen it a quarter turn. If you over-tightened the filter, you may have damaged the gasket and need a new one. Wipe the area clean and monitor for a few minutes to confirm the leak has stopped.