Lawn mower engines are tougher on oil than most people realize. They’re often air-cooled, meaning they run hot; they’re exposed to dirt, moisture and other contaminants; and many don’t include an oil filter. Adding to the challenge, most push mowers barely use a quart of oil, meaning a small volume of oil is responsible for delivering big protection. Suffice it to say, it pays to maintain your mower for long life. Here’s how to change oil in a lawn mower.
This example uses a typical push lawn mower with a 3.75-hp motor, but the steps will apply to most push and riding mowers.
Step-by-Step: How to Change Oil in a Lawn Mower
Tools you’ll need:
- Ratchet with 3/8″ extension and socket to remove drain plug
- Latex gloves
- Drain pan
- Clean rag
- New motor oil of the correct viscosity
- New oil filter (if equipped)
1) Prepare the mower
Start and idle the mower for a couple minutes. This helps loosen contaminants that have settled in the engine and warms the oil so it flows better. Only run the lawn mower enough to warm the engine to the touch; running it too long will heat the oil so much it may burn your hands when you pull the drain plug.
I like to elevate the mower to ease drain-plug access. Tip the handle down to elevate the front end, set it down on an overturned bucket, and lift the back end and rest it on another bucket.
2) Drain the oil
The next step when changing oil in a lawn mower is to drain the oil. Position a drain pan beneath the drain plug and remove the plug. Wear latex gloves to prevent getting oil all over yourself.
On many mowers, you’ll need a 3/8″-drive extension to remove the plug. Others may require a socket of a particular size. On some mowers, there is no drain plug and you need to remove the dipstick and turn the mower over to drain the oil from the dipstick tube. You can also use a fluid extraction pump in these cases.
3) Remove the oil filter (if equipped)
Few push mowers use an oil filter, but most riding mowers do. Unthread the oil filter and drain it in the drain pan. Wipe the dirty oil off the engine mount and thread on a new filter. Apply a thin layer of clean oil to the oil-filter gasket to help prevent it from sticking to the engine mount, complicating removal next time you change oil.
4) Add new motor oil
Once the old oil is completely drained, wipe the drain plug clean, reinstall it and snug it down without over-tightening. Then add the new motor oil.
Check your owner’s manual for the correct oil volume. Most push lawn mowers don’t even take a full quart. I like to eyeball the amount of oil in the drain pan and add about the same volume. Install the dipstick, ensuring it’s completely seated, and remove it to check the oil level. Continue to add oil until the correct level registers on the dipstick.
How often should I change oil in my lawn mower?
Check your owner’s manual for the recommended oil-change interval. Many manufacturers recommend changing oil every 50 hours, or seasonally.
It’s a good idea to change oil prior to storage. Engine operation creates acids and other combustion byproducts that can damage the engine if allowed to sit all winter. Drain the old oil to remove contaminants so clean, fresh oil is sitting in the engine during storage. It also means your mower will be ready to go in the spring.
Which motor oil should I use?
Make sure to use the correct viscosity of oil. Most lawn mowers require 10W-30 motor oil. However, some may call for 5W-30, 10W-40 or even 15W-50 in some zero-turn mowers. Check the owner’s manual for that information. Some mowers may have the viscosity stamped on the oil-filler cap.
It’s also a good idea to use an oil specifically formulated for small engines. As said earlier, small engines are tougher on oil than most people think. “Small” doesn’t mean “simple” when it comes to mower operation.
Air-cooled mowers can run hotter than your car engine. Throw in some airborne dirt, wet grass clippings, leaves, moisture and other contaminants, and you have a recipe for oil degradation and engine wear.
We recommend AMSOIL Synthetic Small-Engine Oil, which is a commercial-grade formulation that fights wear, helps prevent deposits and provides long service life to ensure your lawn mower runs great and lasts for years.