WD-40 Explained: What’s Really Inside and When to Use It

Where WD-40 Should and Shouldn’t Be Used

Quick Summary

WD-40 is one of the most misunderstood products in the garage. While it can be useful in some applications, it’s often ineffective in others. WD-40 excels at water displacement, light cleaning, and short-term lubrication, but it is often used as a rust penetrant when it isn’t really formulated for that job. Understanding what’s in WD-40, where it shines, and where it falls short will save you time, broken bolts, and frustration.

WD-40 Ingredients Revealed: What’s Actually Inside the Iconic Spray

As someone who’s worked with lubricants, solvents, and penetrating oils most of my career, I get asked one question more than almost any other: what’s in WD-40? The blue can has been around so long that people assume it’s some kind of mechanical miracle fluid. In reality, WD-40 works well precisely because it’s simple, not because it’s magical.

The original WD-40 formula—short for Water Displacement, 40th attempt—was designed to prevent corrosion on missile components. That purpose still explains almost everything about what’s in WD-40 and how it behaves today.

Despite the secrecy around the exact formula, publicly available Material Safety Data Sheets make it clear that WD-40 is just a blend of light solvents and light oils. It’s designed to expel moisture, dissolve grime, and leave behind a thin protective film. That combination is useful—but it also explains why WD-40 is such a poor rust penetrant compared to products designed specifically for frozen fasteners.

No silicone. No Teflon. No graphite. No water.

• Aliphatic Hydrocarbons (e.g., decane, nonane, isoparaffins) ~45–50%—  Solvent base that helps dissolve grime, oils, and rust-scale; penetrates tight spaces.
These account for nearly half of WD-40’s volume. They’re light, low-viscosity solvents that dissolve oils, greases, and mild corrosion. They also evaporate quickly, which is part of why WD-40 doesn’t linger on surfaces.
• Petroleum Base Oils (e.g., mineral oil, light lubricating oil) ~15–25%— These are the real lubricating agents in WD-40, but they’re very light—think of them more like 3-in-1 oil than motor oil. They’re good for freeing up a sticky hinge or preventing flash rust, but they’re not meant for high-load or high-speed applications.
• Hydrotreated Heavy Naphtha (Petroleum) ~25–35%— This is a refined solvent that’s less toxic than untreated naphtha. It helps dissolve residues and displace water. If you spray WD-40 on a wet bolt, it’s this ingredient that helps push the water out.
• Carbon Dioxide (CO₂) <5%— WD-40 used to use flammable hydrocarbon propellants, but today it uses CO₂. It’s safer and non-flammable, making the spray easier to use in enclosed spaces or around ignition sources.
• Fragrance and Dye Trace amounts— Added for scent and distinctive appearance (light amber color).

NOTE: These ranges are approximate and can vary slightly by region due to local regulations. For example, European and U.S. SDSs show similar but not identical chemical identifiers.

Where WD-40 Works Exceptionally Well

I use WD-40 all the time—but only where it makes sense. It’s excellent for displacing moisture in wet ignition components, electrical connectors, and light-duty mechanisms. If you’ve ever dried out a soaked distributor cap or freed up a sticky latch, you’ve seen WD-40 at its best.

It’s also a great cleaner. The solvent-heavy nature of WD-40 makes it effective at removing grease, adhesive residue, road tar, and light surface oxidation. For short-term corrosion prevention after washing tools or parts, WD-40 does exactly what it was designed to do.

Where WD-40 Should NOT Be Used

This is where experience matters. WD-40 is not a long-term lubricant. I don’t use it on door hinges that need lasting lubrication, on bearings, or on high-load sliding surfaces. Once the solvents evaporate, the remaining oil film is simply too thin.

More importantly, WD-40 is not a real rust penetrant. This is where people get into trouble. Spraying WD-40 on a severely rusted bolt might make it look wet, but it lacks the chemical agents that actively attack rust. True rust penetrants use acids, esters, or chelating agents to break the bond between oxidized metal surfaces. WD-40 does not.

Why WD-40 Is a Poor Rust Penetrant

I’ve tested this countless times. Compared to a dedicated rust penetrant, WD-40 simply doesn’t perform. The solvents in WD-40 evaporate too quickly, and the oil left behind doesn’t creep deeply enough under heavy corrosion.

That doesn’t mean WD-40 is useless on rusty parts—it can help displace moisture and clean surface grime—but it shouldn’t be your first choice when dealing with seized fasteners. If you’re trying to break loose a frozen suspension bolt or exhaust fastener, reach for a real rust penetrant, not WD-40.

Understanding what’s in WD-40 explains exactly why it behaves this way. It was never engineered to dissolve rust at a molecular level.

The Bottom Line From the Shop Floor

After decades of real-world use, here’s my honest take: WD-40 is an outstanding water displacer, cleaner, and short-term protector. It earns a permanent place in my shop. But it’s not a substitute for a true lubricant, and it’s not a serious rust penetrant.

Once you understand what’s in WD-40, you stop misusing it—and you start getting better results by choosing the right product for the job.

What WD-40 Doesn’t Contain

There are a lot of myths floating around about what’s in WD-40. Let’s clear a few of them up:

• WD-40 does not contain silicone.
• It does not have PTFE (Teflon).
• It doesn’t contain graphite or molybdenum disulfide.
• It is not water-based.
• It contains no chlorinated solvents, which makes it safer for plastics and electronics.

When people ask what’s in WD-40, they’re sometimes surprised at how simple the answer is: it’s mostly light solvents and light oils. No magic, just chemistry.

©, 2025 Rick Muscoplat