I used to believe using one “right” oil in my gas powered pressure washer was a big deal. I spent my first several years of pressure washer ownership fervently adhering to this idea.
Then I talked to my neighbor, Bill. In his 70s at the time, Bill owned the same pressure washer for more than a quarter-century.
He proudly informed me he topped off his washer with whatever grade of motor oil he had handy — sometimes 10w-30, sometimes 0w-30, sometimes synthetic and sometimes petroleum-based. Then he fired up his pressure washer to show me, and it purred like a kitten.
I was floored. Bill’s approach made me realize I needed to do more research on pressure washer oil, and which type works best. Here’s what I discovered.
Does Pressure Washer Oil Type Matter?
Yes, but probably not as much as you think.
Like all internal-combustion engine machines, gas-powered pressure washers rely on oil to cool and lubricate internal engine parts. They also use a different kind of oil to cool and lubricate the built-in pumps that pressurize water.
Using the wrong oil in either place could damage your machine, or even cause it to fail. So what kind of oil is wrong? To answer that, you need to understand the different characteristics of motor oil, and the importance of each in pressure washers.
Not important: mineral vs. synthetic oil
Most engine oil is mineral or synthetic. (There are also hybrids, but we’ll keep things simple here.) Mineral-based motor oil is refined from petroleum, while synthetic oil is produced chemically in a factory.
The biggest difference between the two? Synthetic oil has fewer impurities. Some folks believe this matters for pressure washers because most models lack built-in oil filters to collect debris and impurities.
Some people think that without a filter, impurities could easily destroy or severely damage a pressure washer. That’s why many people go with synthetic oil in a pressure washer’s engine and pump.
The truth is, your pressure washer will run just fine on synthetic and non-synthetic motor oil. I’ve used both in mine with zero issues over the last decade. My dad put non-synthetic oil in his for nearly 25 years, and it’s always run great.
Moderately important: oil viscosity
If you’ve shopped for motor oil, you’ve probably noticed numbers stamped on the sides of the jugs. These refer to the grade and viscosity of the oil.
Oil viscosity matters. Different machines have different viscosity requirements, based on their design and the typical temperature range where it’s used. Generally speaking, SAE 5w-30 or SAE 10w-30 are good grades for pressure washers, but checking your owner’s manual will tell you for sure.
Very important: non-detergent pump oil
Engine oil is one thing, and pressure washer pump oil is another. When filling your pump with oil, it’s crucial to use non-detergent motor oil to keep things from clogging internally.
Detergent additives can cause the pump to malfunction over time. Never put regular motor oil into your pressure washer pump. Make sure it’s labelled as “non-detergent” oil of the grade recommended in your owner’s manual.
Very important: the right category of oil
Although there’s some flexibility, your pressure washer will be ruined if you make a serious enough oil-related mistake.
Never put two-cycle engine oil into a pressure washer. This type is meant to be mixed with gas, and won’t cool and lubricate your pressure washer engine properly. Also, never use diesel engine oil. It lacks the right properties to do the job.
What Oil Does My Pressure Washer Use?
For the best answer, consult the owner’s manual. You could certainly take an educated guess, and chances are your machine would work fine. But why not trust the experts who designed your washer?
I always check the manual. If I can’t find it, I scour the internet for an online version. I almost always find one.
If for some reason you can’t find any manufacturer recommendations, go with SAE 10w-30 in the engine and SAE 30 non-detergent oil in the pump.
Best Pressure Washer Oils
Non-synthetic oil
I’ve had excellent luck with this 10w-30 oil in pressure washers and other machines.
Synthetic oil
Amazon’s own brand produces my go-to synthetic oil. Just keep in mind that synthetic or non-synthetic won’t make any noticeable difference in how your pressure washer runs.
Non-detergent oil
This is the pump oil I’ve used in my pressure washer for the past 10 years. It works great and has never given me any problems.
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