Wrenching on cars can be rewarding, providing a tremendous sense of accomplishment when you successfully fix something. Repairing your ride rather than going to a dealership or shop can save a fat stack of greenbacks, plus, it can even get you back on the road quicker since you won’t have to schedule a repair.
But auto repair can also be more frustrating than trying to run Netflix with a dial-up internet connection. Some components are hard to get at, others may require special tools to service and then there’s the issue of rusty fasteners. Heavily oxidized nuts and bolts can be exasperating to deal with. Apply too much torque to a particularly gnarly cap screw and it can snap right off, potentially leaving you in a world of hurt.
To help sidestep troublesome problems, a wide range of penetrating lubricants is available. These products are designed to soak into rust and in some cases even dissolve it, so you can get those pesky fasteners loosened and removed. Here are some of our favorite penetrating oils. These recommendations are based primarily on real-world, hands-on experience, but they’re bolstered by reviews from popular shopping websites as well. None of these products are expensive, so there’s no excuse not to have at least one of them in your automotive arsenal.
Kano Laboratories
Even though Kano Kroil penetrating oil is a deceptively old-fashioned-looking product, it is one of the best oils you can buy. Don’t let that antediluvian packaging fool you, Kroil oil works. Apply it to rusted stuck nut or stuck bolt and it soaks into the crud, helping free things up. This 8-ounce can comes with a convenient applicator nozzle that allows you to apply a small amount of product exactly where it’s needed, because a little bit goes a long way. There’s no need to saturate everything in sight. Kroil is safe for use on a range of materials including plastic and rubber, so there’s little need to worry about it reacting negatively should you spill some. Kroil lubricant does not harden or gum up over time, so it lasts practically forever. Unless you’re running a chop shop out of your pole barn, one can of this penetrating lubricant will probably last a lifetime.
B’laster Chemical Company
For more convenience, consider purchasing PB B’laster. Sold in pressurized spray cans, it’s far easier to apply this product to metal parts in hard-to-reach places, or especially to the bottom of horizontal surfaces or parts. PB B’laster has been around for more than 60 years, and according to the manufacture, it’s been the best-selling penetrating fluid since 1957. For a product to have such staying power, it must work as advertised, and PB B’laster certainly does. Spray it on rusted nut or seized bolt and let it do its thing, cutting through crud and oxidation. Not only does PB B’laster help break stubborn rusted parts loose, it also leaves behind a protective coating that can act as a rust inhibitor helping to prevent corrosion on metallic parts from forming in the future.
Liquid Wrench
Liquid Wrench penetrating oil should do most of what the other products on this list can to combat a rusty bolt, but for a lot less money. Not that any of these oils are that costly, but this product is less than four bucks for an 11-ounce spray can, making it about one-third as expensive as PB B’laster. Its special formulation cuts through grease, plus it penetrates rust and corrosion to help loosen fasteners that otherwise seem stuck forever. It’s low in volatile organic compounds and safe to use on metal, painted surfaces and plastic, plus it’s guaranteed to work by the manufacturer.
CRC
What separates Knock’er Loose Plus oil spray from the other penetrating oils on this list? (Well, other than the, ahem, suggestive name.) Can you say freeze shock action? Unlike competing rust penetrant products, this lubricating oil one actually drops the temperature of the contact area, which supposedly helps the oil penetrate quicker and reach deeper. Maybe leave the blowtorch in the toolbox with this one. Knock’er Loose Plus’s low surface tension allows it to soak into metal rust and corrosion while cutting through grease and grime. Based on reviews posted to Amazon.com, it works well and is fast-acting. Some people report that when left to soak overnight it isn’t as effective as spraying it on stuck metal fasteners and then tackling them shortly thereafter. For less than $10 you get an 11.5-ounce can that is able to spray in 360 degrees. Yes, even upside-down.
Fed Pro
Free All is a popular, professional-grade penetrating oil. According to the manufacturer, it contains more lubricant and less solvent than competing products, meaning there’s more rust-attacking sauce to break loose frozen bolts and frozen metal parts to get the job done. Use it on everything from studs and clamps, to oxygen sensors, brake calipers, chains, gears and much more. Aside from a potent formulation, and a more-than-fair price, there are two other feathers in Free All’s cap. First, it contains no silicone, so it won’t contaminate anything if you’re painting a car or other parts. Second, if you’re not 100% satisfied with this product’s performance, the manufacturer will refund your purchase price.
WD-40
Here’s a little secret: WD-40 is not a penetrating oil. Nope. The product that comes in those iconic blue-and-yellow cans is more of a corrosion inhibitor than a true penetrating oil. WD-40 is also a water displacer (hence the WD), keeping moisture away from sensitive metal surfaces, and it easily dissolves grease, grime, sap and reside on a variety of parts. But if you use this to try and loosen stuck fasteners you may be disappointed. Fortunately, if WD-40 is a brand you trust, it offers a range of other products, including a penetrating oil. Like the other items highlighted on this list, WD-40 Specialist Penetrant Spray soaks into rust and corrosion to help loosen even the most stubborn fasteners. It’s also not a problem if you get it on rubber or plastic, plus, like standard WD-40, its blend of lubricants leaves behind a protective film that can prevent rust and corrosion from forming in the future.
Comparison of best penetrating oil for cars in 2020
| Penetrating oil | Product Name | Quantity | Price |
|---|---|---|---|
| Best overall penetrating oil | Kroil | 8-ounce can | $17 |
| Best spray-can penetrating oil | PB B’laster | 11-ounce spray can | $10 |
| Best value-priced penetrating oil | Liquid Wrench | 11-ounce spray can | $4 |
| Best fast-acting penetrating oil | Knock’er Loose Plus | 11.5-ounce spray can | $10 |
| Best paint-safe penetrating oil | Free All | 11-ounce spray can | $8 |
| Best name-brand penetrating oil | WD-40 Specialist Penetrant | 11-ounce spray can | $6 |
5 things to know when using penetrating oil
- Heat is your friend! If you have access to a blowtorch, even a small one, don’t be afraid to use it. Assuming the stuck nut or stuck bolt you’re trying to loosen isn’t touching plastic components or right next to the fuel tank, adding a little heat and then applying the oil of your choice can really help it soak in to rusty metal parts and loosen things up. But be warned: These products are flammable so use caution.
- Wire brushes are a force multiplier. Before applying either oil products or heat, take a moment to hit the fasteners you’re trying to extract with a wire brush. Clean as much of the corrosion and rust off as you can, which will help the penetrating oil soak in more easily.
- Time is your friend. These products are effective, but they can take a while to work, so budget accordingly. If you can, saturate pesky fasteners the night before you plan to go to work so there’s plenty of time for the oil to soak in and do its thing.
- Along with time, multiple applications of a penetrating oil can’t hurt, either. If you’re waiting overnight for one of these products to work, a few hours after the initial soak, it’s not a bad idea to apply a little more to the fasteners that need extracting. This ensures there’s plenty of penetrating oil on the offending components and loosens rust to increase the chances of complication-free removal.
- Finally, don’t expect miracles. Sometimes metal components are just too far gone, and no amount of penetrating oil or heat will make them budge. If, for instance, a metal stud is so rusted that most of the threads have disintegrated, chances are the accompanying nut ain’t coming loose, so plan another avenue of attack, like grinding it off or drilling it out after it inevitably snaps off.
Penetrating oils can make your life easier in the workshop or garage.
Craig Cole/Roadshow
A valuable helper to keep in your toolbox
Do yourself a favor, before heading out to wrench on something in the garage, make sure you have penetrating oil in your toolbox. There are plenty of great options to choose from, and none of them cost an arm or a leg to take on rusty mechanical parts.
When used properly, these products can be worth their weight in gold, making it dramatically easier to remove rusty, crusty fasteners and ultimately complete an automotive repair job. From simple maintenance chores to heavy-duty tasks, penetrating oil is a must-have tool and a great labor saver.
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