What Are Penetrating Fluids And How Do They Work?

Penetrating fluids or penetrants are chemicals comprising of solvents and lubricants designed to free up frozen fixtures.

Nuts and bolts that refuse to budge are every mechanic’s nightmare. It is not uncommon for them to resort to extreme measures to unlock frozen fasteners. Such means include brute force, long arm leverage and sometimes even heat from flame torches.


It is not always possible to free up frozen fixtures by mechanical means without incurring the risk of permanent damage to the components (Photo Credit : Audio und werbung/Shutterstock)

However, these methods are often fraught with risk of causing irreversible damage to the fasteners.

However, it is possible to use certain chemicals that make the process of releasing them easy. These chemicals are known as penetrating oils. Read on to know more, as we will teach you how to make some at home, rather inexpensively!

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What causes nuts and bolts to freeze?


Environmental conditions that promote rusting usually cause seizures or freezing of mechanical fastenings and linkages (Photo Credit : Roman023_photography/Shutterstock)

The manufacturing process of nuts and bolts involves stabilising the exposed metal surfaces to prevent corrosion due to oxidation. When they are tightened, the friction causes the anti-corrosive surface films to wear off. This promotes oxidation which combined with environmental conditions, dust and microscopic debris causes them to seize over time.
Seizing is not restricted to nuts and bolts but other fasteners such as rivets, chain links etc. too.

What is a penetrating fluid?

Penetrating fluids present a viable chemical solution to the problem of frozen linkages and fasteners without having to employ extreme physical means. They are low viscosity fluids composed of a solvent and a lubricant which are engineered to tackle seized fasteners. Let us take a detailed look at how they work.


A penetrating fluid enables motion between seized moving parts by dissolving the rust and debris in the mating surfaces and mobilising it by lubrication (Photo Credit : Aleksey Kurguzov/Shutterstock)

1. The solvent is used to dilute the lubricant, making it thinner and thus more penetrable. This improves the reach of the lubricant, especially in deep seated areas.
2. As the solvent dissolves the debris, the lubricant further frees up the rust, making unlock easier.
3. Penetrating fluids have hydrophobic properties. They leave a thin, moisture repellent layer on the exposed surfaces of the fasteners. This enables them to inhibit further corrosion.

Various types of penetrating fluids

Penetrating fluids have to be engineered differently to be useful in various situations. This can be achieved by changing the nature of lubricants based on the application.

1. Friction based applications

These are the most common applications of penetrating fluids. Friction can be static, such as in nut – bolt and rivet systems, or dynamic such as in chain linkage or even machining operations. Penetrants used in such applications usually contain petroleum based oils that have been diluted by means of solvents like acetone or kerosene. They are usually supplemented by additives to prevent oxidation.


Petroleum based lubricants are used in static and dynamic friction applications. A rusty bicycle chain is a good example of dynamic friction (Photo Credit : twenty20)

2. High temperature applications

Amongst the most commonly used oils in penetrating fluids, direct petroleum derivatives are the most common. However, their low flash point, or the ability to ignite when mixed in air at a given temperature makes them unsuited to high temperature applications.
The best oils suited to such applications are composed of chemically synthesised polymers such as poly-glycols, esters and diesters. Their high flash points make them ideal for such applications.

3. Electrical applications

high-voltage-electric-sub-station_t20_KAm440 (1)

Synthetic lubricants are used in areas such as high voltage transmission lines where the risk of electrical fires is high (Photo Credit : twenty20)

Oils with low dielectric strength or the ability to allow passage of electricity without changing chemical composition are not suited for such applications. Therefore, silicone based oils that exhibit high dielectric strength and water resistance are employed in electrical applications.

Can penetrating fluids be used as lubricants?

Penetrating fluids are often mistaken to be the whole of any given function they are essaying. That is to say, people often use them as a replacement for lubricants or corrosion inhibitor. However, it is important to note that penetrants have these properties as more of a stop gap arrangement rather than a permanent solution.

The solvent used in penetrants is usually volatile, leaving behind a thin film of lubrication which will usually wear out more quickly than a dedicated lubricant such as oil or grease. Similarly, they cannot be used as prolonged corrosion inhibitors. However, inclusion of special additives can enhance a desirable property in the penetrating fluid.

Make your own

For those amongst us with a mechanical bent of mind or love for handyman skills, penetrating fluid can be made at home. Since some chemicals involved in the process are corrosive, it is important to use protective gear like eyewear, respiratory masks and gloves.


Acetone, vegetable oil (optional), automatic transmission fluid (available in most hardware and auto parts stores)


Pump action oil can


1. Clean and dry the metal oil can thoroughly. Acetone chews away into plastic and hence it is recommended to use metal canisters.
2. Take equal parts acetone and automatic transmission fluid and fill them in the oil can. If transmission fluid is not available, vegetable oil can also be used.
3. Seal the can and shake it vigorously.
Acetone is a very potent solvent whereas the oils serve as lubricants while preventing moisture ingress in areas that are prone to rusting.

view-of-metal-clamp-coated-covered-with-wood-chips-dust-sawdust-in-a-workshop-garage-used-to-grip_t20_jL1voN (1)

Acetone eats away into plastic, thus metal oil cans are desirable (Photo Credit : twenty20)

While the downside of the home made product is the slight inconvenience arising from the pumping action, it is often observed to have more penetrability compared to store bought products. // research paper on recipe and penetrability of home made penetrating fluid

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About the Author

Prashant is a mechanical engineer and MBA from NMIMS University, Mumbai. An auto-fanatic with an insatiable need for speed, he is constantly on the look out for new technology in the field of automobiles. When he is not working, he loves to read, blog about cars, test the latest rides on the market and wash his own vehicles.

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