If you are struggling to decide what oil to put in your lawn mower then the old adage is always to check the manual.
If you have lost the manual then you can check good old Google.
Sometimes though, there are some old-held beliefs that linger on for many years. We are going to tackle one of them today:
Can you use non-detergent oil in a lawn mower?
So let’s jump in…
Can You Use Non-Detergent Oil In A Lawn Mower?
You can, but you shouldn’t! Using a non-detergent oil in your mower will lead to sludge build up and the deterioration of the engine. Detergent based oils contain additives that keep the inside of the engine cleaner and stop oxidization. They are the recommended oil in pretty much every internal combustion engine for these reasons.
Non-Detergent Oil and Small Engines: Do They Go Together?
Non-detergent oil lubricates and cools the engine of a lawn mower. It doesn’t remove dirt and grime from the engine.
That is where there the difference lies between detergent oils and non-detergent oils.
Detergent oils, on the other hand, contain chemicals that will clean your engine whilst lubricating it.
They collect dirt and grit in the engine and break it down, so it doesn’t find its way into small parts of the engine to clog it up.
Another difference is that detergent-based oils also contain corrosion inhibitors that stop your engine from rusting over time.
Non-detergent oils don’t contain these additives.
So you might be getting the impression that non-detergent oils should not be used in lawn mowers, right?
Yep, you are dead right.
Let’s expand on what we have learned above, and explain in more detail why.
#1: Non-Detergent Oil is Ancient Technology
There once was a time when non-detergent oil was all you could buy.
Now I am going back a long time here, it was around the 1950s that detergent-based oil began to be developed and marketed widely.
But up until that point, you would have to make do with non-detergent oil.
Things have changed with regard to pretty much every type of small engine made in the last 30 years.
Whether they be splash lubed or pressure lubed, they will all recommend a modern detergent oil.
Non-detergent oils are a thing of the past.
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#2: Non-Detergent Oils Have No Additives
Non-detergent oils have a bit of anti-foamant and that is it.
They have no additives that will protect your engine, such as anti-wear, anti-rust and anti-oxidants.
Basically, all the things that detergent oil has that protect, clean and prolong the life of your engine, a non-detergent oil doesn’t have.
Your lawn mower might run fine with non-detergent oil in it, but it will not be doing the engine any good.
So What is Non-Detergent Lubricating Oil Used For?
After reading all of this you might wonder what non-detergent oil is actually used for!
Well it tends to be used in things like compressors and hydraulic pump applications.
Essentially it is good for non-combustion machines, and equipment that doesn’t want particulate floating around in the oil.
I think machining mills and lathes also tend to use non-detergent oil so the particulate can fall out.
It might also be useful on ancient machines that are very sludged up.
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In a case like this using non-detergent oil might have the benefit of stopping the old debris getting stirred up.
Aside from that save non-detergent oil for your workbench oil can, so it can be used as a general coating on your tools, a substitute for bar and chain oil and on hinges, locks and bicycle chains!
Essentially all combustion engines made in the past few decades will want modern detergent oil.
Should You Use Non-Detergent Oil in a Lawn Mower Without an Oil Filter?
There does seem to be an idea that non-detergent oils should be used in lawn mower engines without an oil filter.
The thinking behind it is that non-detergent oils will allow the dirt and grime to sit at the bottom of the engine, whereas detergent oils will stimulate it and stir it up so it is suspended in the oil that circulates around the machine.
This is another old wives’ tale.
You should still use a detergent oil regardless of whether your machine has an oil filter or not, in fact, it will be recommended by the manufacturer.
The truth is any small engine will have enough turbulence that anything suspended in the oil will be whipped up and circulated in the oil anyway.
But then on top of that, if you are using a non-detergent oil, you will be missing out on the additives a detergent-based oil has that protect and prolong the life of your mower’s engine.
It is a lose-lose situation!
Keep the particles suspended in the oil so they can be drained out when you next change the oil.
It is that simple.
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Final Thoughts
The bottom line is that non-detergent oils do not belong in the crankcase of any small engine.
Take a look at any kind of small combustion engine made in the past three decades, and see what type of oil is recommended.
Without fail the manufacturer will specify a detergent oil.
There is a reason for that.
Detergent oils keep the engine cleaner, stop gum and varnish deposits from forming, and make it last longer and perform better.
Non-detergent oils do not have any of the additives that do this.
If you use them your engine will see sludge build-up and it will rust and wear out much quicker.
You have been warned!