Best Penetrating Oils: Loosen Jammed Bolts and Fight Rust
Loosen corroded bolts, stuck nuts, jammed pipes, rusted screws, and other stuck parts with our top picks for the best penetrating oil.
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BY Heather Fishel / LAST UPDATED ON October 15, 2021
If you’re tackling any kind of auto repair work, you’re bound to encounter a stubborn bolt, rusted fastener, or other types of jammed, unmoving parts and pieces. As your vehicle ages, critical components can become corroded or rusted — and that leaves them stuck in place, frustrating your attempts at repairs. Fortunately, there’s an easy solution to these frustrating encounters: penetrating oil.
With a bottle of penetrating oil, you can lubricate even the most stuck-in-place bolts and other kinds of fasteners. This handy oil will even prevent metal parts from sticking and corroding in place altogether, keeping them moving freely. With a penetrating oil in your garage tool kit, you’ll be ready — and better equipped — to deal with nuts, bolts, and any rusted parts. If you’re looking for the perfect penetrating oil to keep on hand, we’ve got a list of the best options available.
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Benefits of Penetrating Oil
- Lubrication. Most penetrating oils will offer temporary, if not long-lasting (some products have additives in their formula to increase the lubrication effect) lubrication to mechanical parts. The oil will help with reducing friction and will loosen frozen parts or tight bolts and nuts.
- Cleaning agents. Most penetrating oils can also be used as cleaning agents. They can effectively remove tars, greases, rust, and adhesives. The fluid will work as a solvent and will melt contaminants to a point where they are easy to remove using a tack cloth, a wipe, or a light abrasive.
- Corrosion-resistance. Penetrating oils are created to protect metal surfaces from corrosion. Corrosion is the biggest enemy of metals used in constructing mechanical parts. The oil has a formula that works by displacing moisture, which is a big part of the elements that cause rust and lead to corrosion.
- Noise reduction. Penetrating oils help to reduce rust and friction that often leads to squeaky door hinges, windshield wipers, a noisy suspension, screeching bike chain, and other noisy movable parts.
Types of Penetrating Oil
Water-Soluble or Emulsion Penetrating Oil
Water-soluble penetrating fluids have a high water content in their formula. They can also be diluted in water to get a concentration that’s lower than 10 percent. These oil types are best used for materials that can be damaged by highly-concentrated solvents with harsh chemicals in their formulation.
Synthetic or Semi-Synthetic Penetrating Oil
Synthetic penetrating oils are created from synthetic or semi-synthetic compounds such as polyglycol, silicone, diesters, esters, or a combination of water and synthetic fluids. These penetrating oils are more expensive than other products in this industry. However, synthetic oils are fire-resistant and great coolants.
The products under this type are made from base minerals and petroleum oils. The products do not need any dilution to be used and may contain other lubricants such as esters, fats, and vegetable oils. In some cases, the oils will also have other additives such as phosphorus, chlorine, and sulfur, and are great for machine parts lubrication.
WD-40 (Water Displacement-40) is a penetrating oil and water-displacing spray manufacturer based in San Diego, Calif. The company was founded in 1953 and has been providing penetrating fluids under the trademark name WD-40 since then. One of its best penetrating oils for seized bolts is the WD-40 Multi-Use Product.
Kano, officially known as Kano Laboratories, headquartered in Nashville, Tenn., is a company that focuses on producing specialty chemicals. The company boasts of selling its products to 480 of the Fortune 500 companies around the world. The Kano Kroil Penetrating Oil is one of the best rust penetrating sprays under the Kroil name and has been in the market since 1939.
B’laster Corporation is a company that manufactures and distributes B’laster lubricants, rust inhibitors, penetrants, and other specialty fluids for industrial and automotive industries. The company was founded in 1957 and is currently headquartered in Ohio. This company offers some of the best penetrating fluids for stuck bolts and the B'laster Penetrating Catalyst is one of them.
Best Penetrating Oil Pricing
- Under $20: This price level is for the basic-level penetrating oils that are mostly the water-soluble type. Most won’t have a long-lasting lubrication effect but expect to find some of the best rust penetrants in the market.
- $20 to $40: This mid-range price level holds a variety of high-end penetrants that offer both rust-preventive and water repulsion features, to subpar products with the least impressive features. The penetrants here could be either straight-oil or water-soluble products.
- $40 and up: You will find high-end products here. Some of these oils in this category are similar to the ones in the cheaper categories only that they are offered in packs or in larger cans. However, most are synthetic and semi-synthetic penetrating oils.
Lubricity and Viscosity
Lubricity refers to the ability of the oil to reduce wear and friction in moving parts. If you intend to use the product on mechanical parts, you should focus on penetrating oil with a longer-lasting lubricating action. Viscosity is the measure of internal friction of the fluid and ranges from thick to thin. A low viscosity product will penetrate tight spaces faster and will go deeper with only a few drops.
Penetrating oils vary pretty significantly in their temperature tolerance levels. Some of these oils are perfectly suited for high temperatures and a lot of heat; others are only able to handle a certain heat level. Before you choose any particular oil, check the temperature tolerance rating on the container or product description. If you need a high-heat product, a larger temperature tolerance is better. You’ll want to consider where you’re applying the oil too, as parts that generate a lot of heat will need a more stable, capable fluid.
In addition to temperature tolerance, you’ll also want to consider a penetrating oil’s product formulation — or the ingredients used to actually make the oil. While most penetrating oils share certain ingredients in common, different formulas can include different additions or omit critical ingredients. For example, some oils are specifically formulated to be safe on rubber and plastic parts. Others, however, might damage these more delicate materials if they come into contact with the oil. Think about where you’ll be using your penetrating oil most often to decide what kind of formulation you need.
Non-Foaming or Low Foam
There are two common options when you’re picking out a penetrating oil: foaming or non-foaming. Both are a great choice, but the one that’s best for you will depend on how, exactly, you plan to use your oil. Foaming penetrating oils aren’t suitable for coolant or grinding applications. However, non-foaming penetrating oils — or even low-foaming formulas — are perfect for these uses. If you’re unsure where and how you’ll be using the oil within your car, it’s best to opt for a non-foaming or low foam product, just in case.
- Quantity. When buying penetrating oil, make sure you look at the capacity of the products you are interested in and compare with others in the same price range. Always go for larger cans if you intend to use a lot of oil. Also, choose products with no expiration date if you are going for larger quantities.
- Convenience. A spray can that allows you to deliver a stream or a spray is the best option when it comes to convenience. Spray cans are easier to use and will deliver the oil faster and effectively. There are products that come with a straw for precision spraying.
- Environmental friendly. You should at least ensure that you buy penetrating oils made of eco-friendly ingredients. These products will not only play a part in conserving the environment, but they are also safe to use. Consider zero ozone-depleting compounds that are odorless.
- Additives. Penetrating oils can be formulated with a number of different additives — and each additive is meant to handle a particular issue or offer a specific benefit. Extra pressure additives, for example, help prevent wear and tear. Corrosion inhibitors can eliminate corrosion that’s already present or prevent future corrosion from forming. Double-check the penetrating oils you’re considering to find just the right additives for the problems you need to tackle.
- Flash Point. A penetrating oil’s flash point is the temperature at which the fluid itself evaporates into a flammable gas. Like temperature tolerance, flash point is critical because it can make certain oils more volatile and likely to combust. If you’re concerned about temperature, make sure to choose a penetrating oil that has a higher flashpoint so it’ll stay stable even in the face of scorching vehicle temperatures.
Best Penetrating Oils Reviews & Recommendations 2021
- If you are dealing with a stuck bolt that won’t come loose even after using the penetrant, use a heat gun to warm up the bolt and it will automatically expand. You can then wrench it out. However, make sure the penetrant has a high heat tolerance, or keep the heat at a moderate temperature. Do not ignite the bolt if you used a petroleum-based oil to loosen it.
- If you need to use the penetrating oil often, go for larger quantities. Most people do not realize that penetrating oil is available in large quantities because most brands only market smaller cans.
- If the penetrating oil container does not come with a precision straw, you can always get an aftermarket option. There are precision applicators sold separately and will help you deliver the oil in tight spaces. You can also convert a syringe and needle into a precision applicator.
Q: How long does it take for penetrating oil to take effect?
In most cases, you will have to wait for about 15 minutes for the oil to work effectively. It will, however, depend on the quality of oil and what it’s penetrating. Some penetrants will even need a whole hour and some wrenching to get the nuts loose. Using precision applicators can however reduce the action time.
Q: Does penetrating oil provide lubrication?
Yes. Most penetrating oil products provide some kind of lubrication. The problem is that the lubrication will not last long and you may have to use other lubricants. There are, however, penetrants with more lubrication properties than others.
Q: Are penetrating oil products flammable?
A good number of penetrating oil products have low flash points that lead to high flammability. This means that the products cannot be used on hot or fiery surfaces. However, there are some products that have high-temperature tolerance and can remain stable in high-temperatures surfaces like an engine.
Q: Can the penetrating oil be used on aluminum parts?
Unless specified, most penetrating oils will work well with all metals. You can effectively apply the oil on seized aluminum parts and get great results. It is always important to check on the instructions from the manufacturers to see on which surfaces the oil can or cannot be used.
We’ve chosen the B'laster BLP16-PB 12 oz. Penetrant as the best penetrating oil. It works on a variety of components and does not harden or lose its penetrating ability.
Our choice for the best value penetrating oil is the 3-IN-ONE 10038 Multi-Purpose Oil. It’s a hard-working spray that penetrates deeply and quickly.