Treating Wood With Used Motor Oil

by Synthetic Oil | Last Updated: May 7, 2022

Changed your car’s engine oil and find yourself wondering what to do with all that used oil? If you have some wood fence posts in need of treatment, that used oil may come in handy. Used motor oil can protect your wooden fences, furniture, and decking. Naturally, a few questions arise when it comes to treating wood with used motor oil, including can and should you do it.

Time to get to the bottom of this.

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Can You Use Motor Oil To Preserve Wood?

Yes, you can definitely use motor oil to preserve wood. Oil has been used for centuries to preserve a variety of objects, but it wasn’t until the early 1900s that farmers started using old engine oil to protect their fences and barns from weathering.

Due to the chemical composition of oil, it does not rot wood but stabilizes it. Since oil tends to repel water, once it has soaked into the pores of a surface like wood, it keeps water from getting in and causing rot. In other words, oil makes wood stronger. Oil also keeps certain insects at bay.

Of course, there are some downsides to treating wood with used motor oil that will be discussed a little later.

Does Motor Oil Rot Wood?

Let’s first bust a myth. Oil does not rot wood. For as long as you need it, the oil will stay with whatever wood it is applied to because oil doesn’t dry. This is part of the reason motor oil is used to preserve wood—not disintegrate it.

The upside to using motor oil on wood? You get to keep your fences and decking around for longer. Plus, an oil stain looks great—nice and golden brown. The bad side? Oil never dries.

Perhaps that’s where the idea that oil rots wood came from. Since oil remains a little wet and sticky, dust and grime end up caking whatever wood has been treated with oil. Over time, your prettily stained fence is going to end up looking rundown. But at that point, your car may need another oil change!

How Long Does It Take For Engine Oil to Soak Into Wood?

Did you paint a wood bench with oil and expect it to be dry in the morning? Think again! Oil may take a day, week, year, or an interminable amount of time to soak into the wood. The kind of wood used, as well as the thickness, can prevent the outside from feeling dry to the touch. Drier wood draws in oil much faster than wood that has been previously treated.

Also, if you use a very thin layer of used motor oil, the wood dries faster than if you slather it on thick.

Did you mix used engine oil with diesel? That makes the mixture thinner, so it will soak more quickly than straight motor oil.

The Drawbacks of Used Engine Oil on Wood

Do you remember those drawbacks that were mentioned earlier? Choosing used motor oil is a good option for those who want to recycle old engine oil and live in a less humid climate. But that doesn’t mean there aren’t things to consider:

• Smell. Let’s face it. Oil kind of stinks. Even if you go with a 50/50 engine oil and diesel mix, the stink of motor oil is always going to linger. That means you might want to avoid using engine oil on your wooden outdoor furniture or any interior applications.
• Flammability. While motor oil is not flammable like gasoline is flammable, it does pose a risk. Arid climates increase the chance of spontaneous combustion. This is true for linseed oil, too. Plus, when oil does start to go a little dry, it tends to release toxins.
• Toxicity. Oil may never cure or dry completely (especially somewhere humid), meaning that there is always a chance that oil is going to seep from the wood into the ground. Outside, this means a contaminated lawn.

For these reasons above, you never want to treat your furniture or flooring with used motor oil. Only use safe materials, like tung oil and mineral oil, or specially formulated wood stains for that.

How to Treat Wood and Fence Posts With Used Motor Oil

So you have decided that you want to stain your fence with used engine oil. It’s going to be a bit of a messy job (and also a potentially dangerous one). The first thing you need to do is prepare the area where you will be working. Never handle motor oil without gloves and goggles, either. A safety mask to filter out fumes is also recommended.

Next, follow these steps:

Filter The Oil

While this isn’t necessary, you may want to filter any particles or pollutants out of the oil. In order to filter dirt and sludge from the motor oil, put some cloth inside a funnel. Pour the oil down the funnel and into a clean reservoir. If you plan on painting the fence, the filtered oil can go right into the paint tin and bucket.

Mix The Motor Oil With Diesel

Yes, you can put engine oil directly on your wooden fence. It doesn’t mean it is a good idea. Applying used engine oil without mixing in diesel means two things: It will take longer to soak in, and the oil may run off during the next rain, becoming an environmental issue. The best ratio is 50/50, so a 1:1 mixture between oil and diesel.

Pour the diesel into the oil then shake up the mixture to blend it thoroughly. Adding diesel thins out the oil a little, making it easier to apply and soak in. You can also pour this blend into a spray bottle for quick application.

Paint or Spray Your Fence

The last step is to either paint or spray down the fence. Painting your fence with oil can take a long while, but it does ensure that each layer on the fence is even. However, if you want to get this project done as fast as possible, spray paint the fence with used motor oil instead.

Final Thoughts

Can you treat wood with used motor oil? You can, and there are benefits to it. However, you need to be careful how you apply it. Make sure you are using a 50/50 mix between oil and diesel. Also, due to the nature of engine oil, you should probably only treat wooden fences and posts with it instead of anything you will be sitting or walking on!