What Happens If A Lawn Mower Has No Oil? (Hint: It Isn’t Good…)

Oil can next to window

Many of us have heard the dreaded engine knock at one point or another, whether that be with a car or a mower.

If you haven’t I hope you never do!

It often signifies one thing, which we are going to explore in this blog post:

What happens if a lawn mower has no oil?

Let’s find out…

What Happens If A Lawn Mower Has No Oil?

The most common consequence of running a lawn mower without oil is a completely seized engine, that will not work again. Though on some occasions if a mower is run with oil for just a few seconds, you might be able to get it working again. Otherwise, the lack of oil will quickly increase friction, increase heat and increase wear on the engine, none of which are good.

Before we dive into the dangers of running a lawn mower without oil, it is important to understand the exact role of oil in an engine.

Whether your mower has a two-stroke or four-stroke engine, oil does largely the same job.

  • It lubricates the moving parts of the engine, so they can move smoothly and without friction.
  • The smooth operation of the engine means it stays cool.

And in a nutshell, that is it.

So the big question is…

What Happens If You Run a Lawn Mower Without Oil?

#1: Metals Parts of the Engine Will Rub Against Each Other

As you have probably guessed from our discussion above on the importance of oil, without anything to lubricate them the metal parts of an engine will rub up against each other.

Most significantly the piston rings will wear and warp and most likely fail.

But in general, with parts grinding against each other due to the lack of oil, small metal pieces of various parts of the engine will eventually break off.

These broken bits could clog other engine parts.

And the once smooth and perfectly shaped internal parts will become jagged, broken and abrasive. 

And as they continue to rub up against each other without oil, the damage in the engine will become more severe.

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#2: The Temperature in the Engine Will Increase

Temperature gauge

The lack of oil and increase in friction means one thing, the temperature inside the engine will increase rapidly.

Parts of the engine will likely being to melt and weld together.

#3: The Seals and Gaskets Will Melt

The excess heat will also cause the seals and the gaskets within the engine to melt.

These seals are what keeps the oil in the engine in the first place. As your engine gets lower in oil, the temperature will increase, the seals will degrade and any oil left will quickly escape from the engine.

#4: The Engine Will Seize

And this is what it results in.

A combination of all of these factors will lead to the engine seizing and the blades stopping spinning.

The damage is likely to be permanent and the result for you will most probably be a new lawn mower.

An engine can temporarily run without oil.

Sometimes there is enough residual oil left on the walls of the cylinder, or at the bottom of the crankshaft thanks to gravity, for it to start up.

But if you run any engine without oil, it will not last for long…

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Lawn Mower Low Oil Symptoms: What You Need to Be Aware Of

If you have got this far in the article, then you probably already have a good idea of what is a sign your mower is out of oil, but just in case you aren’t, these are some telltale things to look out for:

  • Noise
    If your engine makes a knocking or grinding noise when you turn it on, or whilst you are running it, then turn it off immediately. Irregular noises from your engine are a sign it needs its oil topping up.
  • Overheating
    As we have already established lack of oil means increased friction and increased heat. If you start to feel any abnormal heat coming from your mower turn it off immediately.
  • Smoke
    Smoke coming from anywhere or anything (apart from a fire!) is not a good sign! Smoke coming from your mower can actually signify either too much or too little oil, neither of which are good. Black smoke from the exhaust pipe usually means too little oil, whereas bright white or blue-colored smoke means too much oil. Either way stop mowing immediately.
  • Your Mower Stops Running
    If you get this far you may have gone past the point of no return already! If the engine seizes completely and the mower stops running check the oil level as that is often the cause. If it isn’t you may have another problem which could be less serious.

What Should You Do If You Accidentally Run Your Mower Without Oil?

The longer you run a lawn mower with no oil, the less likely you are to escape irreparable damage.

However, if it was literally just a few seconds, then all might not be lost.

Turn it off, wait for it to cool and then turn your mower on its side and try manually moving the blade. If the pistons move, even if it is a real effort, then you might be able to get it going again.

If they don’t unfortunately your mower is likely to be a write-off.

But if the piston does move, first of all add the correct amount of oil to the oil filter.

Then try adding some diesel or auto gearbox fluid via the spark plug hole as this is good for pistons that have seized through corrosion.

Leave it to soak for 24 hours.

Then try and start it with the plug out, as you don’t want any compression to impede movement.

Fingers crossed it works!

How to Check For Lower Oil in Your Lawn Mower

Rather than waiting for one of the symptoms of low oil in a lawn mower to present itself, it is far better to keep a regular check on the oil levels yourself.

For four-stroke engines simply remove the dipstick from the oil tank and check the oil level.

The dipstick will have two marks on it, one representing the low oil level and one representing the full level.

The best time to do this is when the engine is cold and the mower is on a level surface.

When you check the level of oil, it is worthwhile checking the color of the oil as well. 

It should be amber and free of debris. If, when you pull up the dipstick, you noticed debris stuck to it and the oil is black then an oil change is probably called for.

Don’t always assume a new mower will come with oil in it. It should do, but it isn’t a guarantee, so check before using your mower for the first time.

Checking the oil level in a two-stroke mower is not as easy, but you will need to add oil to the fuel itself to get it to run.

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How Often Should You Change the Oil in Your Lawn Mower?

If you have your lawn mower’s manual that will give you the most accurate timeline for changing the oil in your lawn mower. 

However, it is generally acknowledged that for walk-behind mowers, you should change the oil once per season or, at the most, for every 50 hours of use, whichever comes first.

For riding mowers, that figure is once a season or every 100 hours of use.

It is important to check your mower’s oil levels regularly regardless of this, however.

Final Thoughts

What Happens If A Lawn Mower Has No Oil infographic

Running a lawn mower without oil for anything more than a few seconds is often very damaging to the engine.

In all honesty, the likelihood is that the engine will have seized and you might need a new mower.

That said, in some instances, you can bring your mower back from the brink of death with a bit of luck and some tlc.

Check on your oil levels at regular intervals as it is much cheaper to buy a can of oil than it is a new lawn mower!

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