The principle of any multipurpose oil is to fulfil multiple functions: Lubricate, clean, protect (corrosion), displace moisture, and, penetrate seized nuts and bolts.

While it may be tempting to debate which brand is best in each function, that’s similar to debating which multi-tool has the best knife for a butcher, or the best screwdriver for a carpenter.

In other words, if your job consistently involves loosing overly tight or seized components, then a dedicated penetrating oil is what you should be using. Not a multi-purpose spray.

On that note, the essential qualities of a good penetrating oil are…


Needless to say, seepage is a given requirement, and the viscosity of the oil is what generally determines this. It’s also one of the reasons why a dedicated penetrating oil is preferred to a multipurpose spray in specific applications.

An oil’s lubrication and corrosion-prevention properties are largely dependent on its ability to “stick around”. This means that thicker oils tend to offer better corrosion protection and lubrication over the long term. However, this is in contrast to what’s needed for a penetrating oil, where a thin viscosity allows for seepage into tight spaces.   

That said, using a penetrating oil as a dedicated lubricant or corrosion inhibitor will not yield great results; and in much the same way, any multipurpose oil that claims to have great penetrating properties, has probably made a few sacrifices in the way of lubrication and corrosion protection. It’s a game of balances.


A penetrating oil’s ability to breakdown rust is an obvious feature, and the only way to achieve this, is to include a small concentration of an oil-soluble acid. Naturally, this does add to the cost of the product, but in extreme environments (i.e. marine applications), such an additive may have a significant impact on the product’s effectiveness.

However, the seizure of a bolt or nut isn’t always corrosion related, and in many cases, it can be due to dust and other soil contaminants. In these instances, you want a penetrating oil that boasts a high solvent strength for its ability to dissolve old oil, grease, and a build up of sand and dirt. Earth moving equipment is a great example.


Of course, just because the fastener is now loose, that doesn’t mean the job is done. Presumably, you’ll want to refit the component you’ve loosened, which is why some form of corrosion prevention is key to making the job easier the next time.

As mentioned previously, thinner oils tend to perform poorly as long-term corrosion inhibitors, but that’s where the use of additives come into play. While cheaper oils may skip this addition, a high-quality dedicated penetrating oil will include some form of corrosion-inhibiting additive. Again, such an additive will raise the cost of the product, but the fee is nominal when compared to future down time and work hours. 

On that note, if your day-to-day job, or weekend hobby, frequently involves stubborn nuts and bolts, then check out CRC Industries’ globally acclaimed KNOCK’ER LOOSE, or our very own Q-PENETRATING OIL

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