What Happens When A Lawnmower Runs Out Of Oil?




Lawn Mowing engine without oil PV

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Why does a mower need oil?

Oil is the something that you take for granted in your mower and never give a second thought until it runs out. I have seen the damage it can do when you run a mower without oil.

So what happens when a lawnmower runs out of oil? Oil is the lifeblood of an engine. It lubricates the moving pasts and reduces friction, therefore, keeping the heat under control. If an engine runs out of oil it will cause friction inside the engine, causing it to overheat and fusing the pistons and stoping (seizing) the engine. This can also cause irreversible damage to the engine.

Most lawnmowers will start without oil (some newer models won’t) and if you realise and shut it off quickly enough you may be ok. Just top up the oil to the correct height and try again. If the mower starts that is a good sign. Do listen out for any unusual noises though like engine knocks. If that happens your engine will need repairs. If the mower sounds alright then you may have just got away with it. 

How do I know if my engine is seized? 

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The easiest way to tell is to pull the starter cord. If you can pull it out then the engine is turning over and the mower is not seized. This is not foolproof though as sometimes the engine if the engine is hot, it will not seize until it cools down.

Another method is to check it to try and turn the blade. (take the spark plug out first). If it turns then the engine is not seized. If you can’t move it then your engine has seized.

how long can a lawnmower run without oil?

A domestic lawnmower will seize quicker as it sits for a while between uses where gravity helps the oil to settle in the sump but regardless of whether you are using a domestic or commercial mower you would be lucky to get five minutes before the machine seizes.

If you are really lucky (and paying attention) you may hear a knocking noise coming from the engine and shut it down before it seizes. Even this does not always work as I have had workers shut machines down within a few minutes but once the engine cools down the engine seizes anyway. 

Will lawn mower smoke if low on oil?

No, this is a misconception. A mower smokes if it has too much oil, not too little. The smoke is caused because the excess oil is being burnt off so low oil equals no smoke. 

Will my lawnmower shut off automatically if it is low on oil?

If your mower has a low oil switch it will, but these switches are not that common.

A low oil switch monitors the pressure inside the engine and shuts the engine down if it falls below a certain level. Then all you need to do is top up the oil and the engine will start. Some newer mowers have a low oil switch which will automatically engage if the mower runs low however it is not a good idea to rely on this. 

Relying on a low oil switch is a bit like only putting oil in your car only when the oil light comes on. It may sound like a good idea but you really don’t want to rely on it. 

Will an engine start without oil? 

Some newer engines are designed not to start if they have no oil but most engines are not. A standard lawnmower will start without oil but will not run for long. You are a lot more likely to hear a knocking noise coming from the engine immediately after starting. This will give you a 30-second window to shut it off without causing irreversible damage. 

How do I know how much oil is in my machine? 

If you have a four-stroke, the easiest way is to use the dipstick. It is better to do this when the engine is cold as it makes it easier to read the dipstick. Do make sure that your machine is level before checking the oil otherwise you may get a false reading. 

What do I do if my lawnmower engine has too much oil?

This is an easy fix. All you need to do is take remove the oil cap and tip the excess oil out of the mower. Do make sure that have removed the dipstick and you tip that side towards the ground and not the side with the air filter. Tipping the filter side will cause the oil to run into your filter and cause damage. 

This collection at my local mower shop contains a few sezied engines.

How do I check if my two-stroke fuel has oil in it?

If you have a two-stroke the is no real way of telling if the already oil in the petrol or not. You could try tipping it in a glass container. If it has oil it will form a darker layer on the bottom if left overnight. 

If you have a two-stroke and you have too much oil it causes smoke and you will need to replace the fuel. There is no real way to figure out how much oil is mixed with the petrol in the machine.

Can you fix a seized lawnmower engine?

You may be able to get a seized engine fixed. It really depends on how long the engine ran without oil. In the case which I talked about earlier in which the engine was turned off before seizing but was found to have seized anyway when it cooled down, it may be recoverable.

When an engine runs without oil it creates friction which in turn overheats the engine. If the engine got to the point where it starts fusing inside (which is the most common scenario) it is unrecoverable.

If the engine did not get to that stage you may be able to disassemble the motor and methodically lubricate the moving parts and get the engine running again. 

In the last thirty years, I have dealt with over a dozen seized engines and from memory around three of them were recoverable. Not the best odds in the world but it still allows some room for hope. 

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