10 Best Penetrating Oils of 2021

Jerry Wilson
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Nowadays, we’re finding more and more uses for liquid penetrant inspection, but it’s much more complex than apply some solvent and check for flow out.

We’re seeing more and more configurations, whether they be discreet cracks or voluminous voids.

Once you’ve found your target, how do you know when you’ve found it?

We’re offering you 10 of the best penetrating oils to use for optimum performance. We’re also giving you an insight into manufacturers, designers, and scientists to help you choose the best.

Kano Aerokroil Penetrating OilBest OverallKano Aerokroil Penetrating Oil
B'laster – 8-PBBudget PickB'laster - 8-PB
Kano Sili Kroil Penetrating Oil King SizeUpgrade PickKano Sili Kroil Penetrating Oil King Size

1. Kano Aerokroil Penetrating Oil

Our rating: 9 / 10

Kano Aerokroil Penetrating Oil

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  • Doesn’t damage paint, plastics, or glass
  • Creates a great barrier
  • Impressive penetrating properties
  • Protective against corrosion
  • Affordable


  • Spray doesn’t always work
  • Doesn’t flow as freely as some other oils

When it comes to penetrating oils, you will find the Kano Aerokroil Penetrating Oil, 10-oz Aerosol version to be a pretty effective tool.

It is devoid of rust inhibitors, petroleum distillates, harmful solvents, and other dangerous chemicals.

This is an aerosol version that helps you spray the oil on the surface to be treated. It will not only penetrate and prevent corrosion, but also create a protective barrier to avoid rust from occurring.

2. Kano Kroil Penetrating Oil

Our rating: 9 / 10

Kano Kroil Penetrating Oil

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Kano Kroil Penetrating Oil is an industrial strength penetrating oil that can get into rusted nuts and bolts. It works on an almost molecular level to loosen the rust on all types of metals.

The Kroil oil is a low odor, easy-cleaning oil making it a great option for your garage or shop. This penetrating oil is made for small mechanical parts, joins, hinges, locks, sliding pins and sleeves. This product comes in a 8 ounce brushed stainless steel can and each can will go a long way in your workshop.

The Kano Kroil oil excels in the compact oily lube formula and improves the speed in which almost anything can pass through.

3. Castle Thrust Penetrating Oil

Our rating: 9 / 10

Castle Thrust Penetrating Oil

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  • Removes the toughest of rust and stuck metal parts
  • Does not leave behind residues or toxic chemicals (Love this! Don’t want to breathe toxic fumes when I barely get enough air in my lungs!)
  • Ideal for lubricating hinges that stick
  • Leaves no after taste on the skin
  • Easy to apply
  • Affordable


  • Only sold online
  • No oiler included

Castle Chemical’s ASTM-rated tungsten carbide coated Thrust is my choice in penetrating oil. It is used by professionals in the construction and manufacturing industries to remove the toughest of rust and stuck metal parts.

Castle’s Thrust is non-conductive, which makes it safe for use in electrical components including switches, controls, and motors.

The best thing is that it does not leave behind residues or toxic chemicals, which means it’s safe to use around your home.

4. Kano Sili Kroil Penetrating Oil King Size

Our rating: 9 / 10

Kano Sili Kroil Penetrating Oil King Size

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  • Made in the USA
  • 25% Thinner That Most Other Penetrating Oils
  • Does Not Evaporate as Other Penetrating Oils
  • Kano Kroil is a Proven Wonder

Kano Sili Kroil Penetrating Oil King Size, 16.5 oz aerosol is the best among the others. It comes at a premium price, but it’s worth it. I used it for the first time a while back. As soon as I finished the project, I started looking for the best penetrating oil available on the market and found this product.

Basically, it’s easy to use and clean up. The product comes in a 16.5 ounce aerosol can. It is recommended to use 1 -2 ounces of it to have it penetrate all problems. You have to coat the problem area and wait, when the product is dried you can start drilling or using a wrench again.

5. B'laster 16-PB Penetrating Catalyst

Our rating: 9 / 10

B'laster 16-PB Penetrating Catalyst

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  • Repels water
  • Stays effective in extreme temperatures
  • Works well on rusty nuts and bolts
  • Pays for itself in a short period of time

I have to admit that I was a little skeptical about using penetrating oil to loosen up rusted nuts and bolts. I had always relied on more traditional methods, but a friend recommended I give B’laster a chance.

B'laster is fantastic at getting to the rustiest nuts and bolts. I've had reliable results sprayed on and working over night. However, it works faster if you use a wire brush to speed up the clean up process.

This oil leaves behind a clean, dry surface, preventing the corrosion from spreading.

6. CRC KNOCK'ER Loose Solvent 13 OZ

Our rating: 9 / 10

CRC KNOCK'ER Loose Solvent 13 OZ

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  • Can Remove Rust & Loosen Rusted Parts
  • Works Well With Difficult Loose Fasteners
  • Works On Most Applications
  • Not Highly flammable, unlike other leading brands
  • Has a Strong Pleasant Odor
  • Easily Cleans Up W/Water


  • May seep into small cracks in metal parts & drain out the bottom
  • Possible to drip on paint, then you will have to sand it off.
  • Not ideal for indoor use due to strong odor
  • You need to wear gloves to help prevent severe skin irritation

We've been using CRC Penetrating Oil for a while now. It has some sort of applicator on the end of the nozzle. I don't know what else to call it, I've never seen it before. Since the metal nozzle block has a control for the flow of the "knock'em loose" engine oil, I would think it is a great way to conserve the oil. One squeeze comes out a small amount. That way if you don't have much to do, you don't waste it.

7. WD-40 Multi-Use Product

Our rating: 8 / 10

WD-40 Multi-Use Product

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  • Available in 4 pack
  • Can be applied on a wet surface
  • Water-based, non-toxic solution
  • Can be sprayed upside down
  • Dries without leaving residue
  • Can be used with tools, toys, motorcycles, and more
  • Ideal for bolts, locks, zippers, and moisture…
  • One of the earliest formulas to date


  • Not ideal for unfinished wood
  • May cause rusting if used on metal
  • Not Kosher certified
  • May not work on black surfaces

Most of the spray…s ingredients are biodegradable and one of the best in the industry when working on tractors. The low-evaporation formula works better on metals than anything else and contains the best adhesive in the business for 15 and another for 500 degrees.

It works well on everything and doesn’t freeze, although depending on the weather, it may take a little longer to thaw. With few exceptions, WD-40 is a spray for just about everything and anything. If you’re wondering why it’s so potent, it’s because it’s made from fluorocarbons.

8. Loctite 503054 Penetrating Oil

Our rating: 8 / 10

Loctite 503054 Penetrating Oil

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  • Price/Value
  • Good quality
  • Maintains effective lubrication for a long time


The Loctite 503054 penetrating oil, 12oz is one bottle of penetrating oil that may be the best of its type on the market. It possesses a strong solvent penetrant and lubricant that is high in performance and can be used for a wide range of purposes.

A penetrating oil is made to be very thin in consistency. The reason for this is so that it can seep through tightly assembled parts or elastically deformed parts that are bonded together. The oil is also able to lubricate the area so that it can slide out or loosen going out without any need for a lot of effort.

9. B'laster – 8-PB

Our rating: 6 / 10

B'laster - 8-PB

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  • Easy to apply
  • Contains a built-in penetrant
  • Dries fast
  • Safe for copper, brass, and aluminum
  • Convenient trigger sprayer


  • Not made for wood
  • Expensive

The B'laster penetrating oil is one of the best prolubes in the market. It comes with a built in penetrant and is great for loosening bolts and nuts jammed even after extensive usage. It's highly concentrated, which means that it effectively penetrates the fastener and lubricates the metal surface.

The solution can penetrate the tiniest of gaps and loosen nuts and bolts that have been fashioned tightly with rust. B'laster also has a built in rust inhibitor that keeps the metal from oxidizing. The product is VOC compliant and is non-toxic, which means it doesn’t irritate the skin and you can spray it around children without being concerned about harming them.

The product is also easy to apply. You simply spray the area on which you want to use it, and wait for the product to penetrate and break up rust. Then, you take your wrench and use it to loosen the nut and bolt. This product is an excellent choice for those who work in a professional environment or as a hobbyist.

10. 3-IN-ONE Multi-Purpose Oil

Our rating: 6 / 10

3-IN-ONE Multi-Purpose Oil

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  • Great Penetrating Power
  • Makes Things Easier For You

What makes this product so special is the fact that it works on so many different things. You can use it to clean your tools, to ease the process of removing stuck bolts & nuts, or even to lube up your garage door. It’s even used by auto repair shops to aid in the process.

It works on most things, so you can use it for any situation that requires you to remove or put something together. It’s also great for loosening up rusty parts. I’ve even heard of people using it to loosen-up a stuck deer’s leg when it was caught in a trap.

This 3-in-1 oil can works to prevent rust and chipping, so you can have your tools for years to come. The only issue you’ll have with this product is the fact that it’s oil tends to cause surface stains. So, make sure to keep it contained an if you spill it.

Frequently Asked Questions (FAQ)

What is the best penetrating spray?

Penetrating oils will make it easier for you to loosen rusted parts or get broken parts out of a mechanism. If you need to fix a broken engine or a toy that’s been in the closet since Christmas, an adhesive might help you get the job done.

But what is the best oil for you?

While we can’t make recommendations for the best brands of penetrating oils on the market, we can point you in the right direction for creating your own. The basic formula is 3 parts mineral spirits to 1 part kerosene, however, you can tinker with that as you see fit. Mineral spirits are typically available at your local hardware store, while kerosene can be found online or from larger hardware chains.

What can I use instead of penetrating oil?

You can use the following ingredients to make your own penetrating oil mixture. Some experts recommend mixing these with a vegetable oil, while others recommend rubbing them together on their own. In either case, use equal parts olive, grapeseed, and coconut oil.

One of the most important things you can do is ensure your sidekick is dry. If not, then your penetrating oil won’t be able to work as effectively. You could wipe down the area with a cloth, or if you need something a little larger, try a T-shirt (which is basically made out of the same material).

It’s worth noting that some people recommend against using glue from your craft supplies. This type of glue might not bond well with your plastic and could ruin it. We recommend using something that is designed to bond to metal or plastic.

Is there anything better than wd40?

If you've never used penetrant oils before, then you obviously aren't aware of the best tools available. The wd40 is a great product and has stuck around since its invention because of its simplicity and effectiveness. However, there are many better choices available than the wd40.

Wd40 works fine when it comes to lubricating and loosening, but it has a tendency to evaporate. Wd40 doesn’t give you a synthetic lubricant, and it’s not something that will bond to surfaces. For example, if you use wd40 to loosen a stubborn bolt or lug nut, you're going to spend time cleaning the excess spray off the part. As a result, you may find yourself using a lot more wd40 than you have to.

What are penetrating oils for hair?

Penetrating oils are ideal for those who spend a lot of time working their hair with hot tools. Penetrating oils are like other hair oils but with an extra oil that can seep into the hair shaft and lock in moisture. The oil acts like a sealant making it harder for the head to become dry and damaged.

The right penetrating oils can protect against hot tools, UV damage, and shampoo build-up.


With so many fluids penetrating fluids out there, we did the hard work of testing them. Although there are many great penetrating oils, we have identified the ones that stand out from the rest. These oils will make short work of various fasteners that are deemed hard to remove.

Our team of experts has tested a number of penetrating oils to analyze their abilities to loosen difficult parts. We have selected the most effective, top penetrating oils for the largest variety of situations. Now, we are providing you with our expert advice and what tools to look for when searching for a oil you can trust.

Our Recommendation

Kano Aerokroil Penetrating OilBest OverallKano Aerokroil Penetrating Oil
B'laster – 8-PBBudget PickB'laster - 8-PB
Kano Sili Kroil Penetrating Oil King SizeUpgrade PickKano Sili Kroil Penetrating Oil King Size