You forgot to change the engine oil in your lawn mower. Now you want to know what damage can happen to your engine. I have seen many failed lawn mower engines due to running dirty oil in my years as an outdoor power equipment service manager.

There are many people who are under the misconception they don’t need to change the engine oil in their lawn mower. This is so not the case. The oil in the engine does more than people think.

If you don’t change the oil in your lawn mower, the oil becomes very dirty and breaks down. The oil loses its cooling agents and detergents which can cause significant damage to your engine.

People often don’t think about putting money into their mower until the mower doesn’t start or encounter other engine problems. Give your mower a little bit of attention once or twice a year and you will be surprised how long that mower can last you.

engine damage is likely if you skip oil changes

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating.Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

What Does Engine Oil Do in a Lawn Mower?

The average lawn mower’s small engine only holds about 3/4 to 1 quart of oil. This engine oil is usually an SAE30 weight oil. That little amount of oil has a lot of work to do in such a small space.

Remember, it’s only getting cooled by the air revolving around the engine. That means if it’s 80 degrees outside, your oil is already going to be that warm.

Oil will break down over time. All the cooling agents and detergents in the oil will eventually disappear or break down. The ingredients in our oils are designed to do a lot of things:

  • Acts as a cooling agent that keeps the internal parts of your engine cool while it is building heat from friction
  • Acts as a buffer between moving parts. These moving parts build heat in the engine.
  • Acts as a cleaner. It keeps carbon and broken down oil from clogging up oil passages in the internal routes of the engine. If these routes get plugged oil cannot get through which can damage the engine.

What Happens When I Don’t Follow Manufacturer’s Oil Change Guidelines?

Most small engine manufacturers say engine oil should be changed every 25 to 50 hours of use. The hourly interval depends on the capacity of the engine and how hard it gets used.

Sometimes when you use the mower harder and longer than normal the temperature of the engine will rise considerably. Running oil in an engine to higher-than-normal temperatures is when weak oil has a chance to fail.

When the oil in your engine gets overheated it becomes black and thick in consistency. This thick black oil bakes onto the internal parts of the engine. Oil can no longer flow over and around these parts as easily as it was designed to.

Taking time to change your engine oil regularly will ensure your engine lasts more than a couple of years. The price of a quart of oil is a pretty inexpensive insurance policy. Think about all it does to protect the engine and its components.

Should You Replace the Engine or Replace the Lawn Mower?

Remember, if you don’t change your engine oil you could end up with the expense of replacing the engine. The engine is the main component of your lawn mower. If it fails, you need to consider a couple of options before making an additional investment in your mower.

Should you replace the engine or replace the lawn mower? You will want to take the expense of a new engine and the life span of the mower into account when deciding to make a significant engine purchase.

An engine can be replaced in a lawn mower without too much trouble with the installation. The cost will be the biggest factor you will want to consider before purchasing a new engine.

A replacement engine will cost anywhere from $200.00 up to $2,700.00 depending on the manufacturer and horsepower.

Replacement engines can be purchased online or from your local engine dealer. Engines can look similar when shopping on the internet, but it may not be the correct engine you need. Make sure you have your model and spec number to purchase a compatible engine.

You will also need these same numbers if you want to order parts for your engine. If you are unsure whether you are selecting the right engine online, you may want to purchase from an engine dealer.

The knowledgeable staff at the dealership will be able to assist you in finding an engine that will fit. You should consider, in addition to cost, the condition of your mower.

Are you going to have to put a lot of money into the frame, shell, or deck of the lawn mower anytime soon? It may be more cost-efficient to purchase a new mower rather than put additional investment into an old mower.

Why am I Always Adding Engine Oil to My Mower Each Time I Mow?

It’s always good to check the level of your engine oil before you mow. If you find yourself always adding oil to your engine before you go out and mow that’s not always a drastically bad thing, but it’s also not a good thing. You need to find out why you always have to put oil in your engine.

You may be adding oil to your engine each time you mow because you have an oil leak, your engine is burning oil or your engine is using oil. You need to identify which one of these scenarios applies to your engine oil loss.

  • Oil Leak – Look over the engine area to find signs of an engine oil leak. Once you find the cause of the leak, replace the gaskets from which the oil is coming leaking. You will also want to inspect your filter if your mower uses one. Make sure your oil filter is sealing properly.
  • Burning Oil – Check for a plugged air filter. A plugged air filter will cause oil to burn from the engine making the engine work harder. You can clean the air filter or replace it is very dirty and unable to be cleaned.
  • Using Oil – An engine can be using oil due to overheating while in use. It can also be an indication of a valve or ring problem. You need to take your mower to a repair center for an engine diagnosis.

Items Needed for an Engine Oil Change

Selecting the Correct Engine Oil

Make sure you select the correct engine oil before your oil change. Most gas-powered small engines will use SAE30 oil with the exception of Kohler engines.

Kohler engines will need a 10W-30 due to the hydraulic lifter inside the engine. Most engines take 3/4 of a quart and up to 2 quarts for larger engines.

Oil Collection Container

Find an item to collect the oil in. A drain pan is best. If you don’t have a drain pan, find a container that has a large enough capacity to hold the used oil and will not leak all over the floor.

Also, make sure you have a closed container for the used oil to take to a recycling center.

You can use empty oil containers. Do not use milk or soda containers. Never dispose of engine oil in the landfill, in your drain, or on your property.


You will need to get the correct size socket or wrench to remove the oil plug. Some plugs are square while others will be a hex plug in varying sizes. A funnel will make adding new oil a lot easier. You will also need a filter wrench if your engine uses a filter.


If your engine is a better type of engine, it will have an oil filter on it. Find a compatible filter for your engine. Refer to your owner’s manual for OEM filters.

If you choose to use an aftermarket filter, there are several websites available to cross reference the OEM filter part number to an aftermarket part number. I always use an OEM filter on my lawn mower engine.

If you choose to use an aftermarket filter, my customers have had good results using this brand.

Other Helpful Supplies

Cardboard or newspaper is useful to keep oil from getting on your work surface. It is also good to have rubber gloves and rags on hand.

Details on How to Change Engine Oil in a Lawn Mower

For more in-depth information on changing engine oil in a lawn mower, refer to one of the information topics:

How to Change Oil in a Push Mower in 8 Easy Steps

How to Service a Riding Lawn Mower: Step-By-Step

How to Change Oil in a Zero Turn Mower

My top items to keep on hand to service & troubleshoot your lawn mower

Socket & Allen Wrench Set – Tool set needed to service & troubleshoot your mower problemsCarburetor Cleaner – Clean clogs & buildup in fuel system
Multimeter – To check voltage, continuity & current to identify electrical problemsFuel Stabilizer – Stabilize & clean your fuel to minimize fuel system buildup
12-Volt Battery Charger – Battery/trickle charger to start your mower & slowly charge your batteryFilter Wrench – Helps loosen your filter
Oil Drain Pan – To collect oil with spout to place in containers for disposalBattery Powered Inflator – Keep your lawn mower tires inflated to prevent uneven cutting or steering issues

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