byMatthew Wright Updated September 19, 2018
The penetrating oil is most useful when you have a corroded or rusted bolt or nut that just won’t budge. Pretty much every home garage or workshop needs a can of spray penetrating oil on a shelf. If you don’t have one, you probably should. But if you already have a can, there is also a good chance you’re using it incorrectly. It’s not uncommon for people to use a can of spray penetrating oil as an old-fashioned lubricant, but that’s actually not what it’s intended for. Spraying a bicycle chain or gear linkage with WD-40 or PB Blaster, won’t really offer the lubrication you wanted.
Penetrating Oil Defined
Although manufacturers vary in how they label their products, the spray oil you are looking for will be called “penetrating oil” or “penetrating lubricant”—even though it’s really not a typical lubricating oil, such as what is used to keep machinery gears running smoothly.
Penetrating oil is a petroleum-based oil with an especially fine viscosity—so fine that it can be sprayed as a mist, and so fine that it will find the smallest openings between metal parts and penetrate them. Because penetrants have such low surface tension, they can seep into almost invisible crevices and over time loosen metal connection that appeared to be rusted solid.
True penetrating oil is sold under many different brand names, including WD-40, PB Blaster, Liquid Wrench, and AiroKroil. This can be a little confusing, especially since brands like the WD-40 offer not only a true penetrating oil but also sell spray lithium or silicone lubricants. And some may be marketed as “multi-use” lubricants that supposedly can be used both for penetrating and other general-purpose lubrication. However, the best products for loosening nuts and bolts and other parts will specify themselves on the label as “penetrating” oils.
Penetrating Oil Uses
When faced with a rusty bolt or nut or other parts that seem corroded together, the secret is time. After spraying a healthy dose of penetrant on the fused parts, give them several hours—or even overnight—to sit while the penetrating oil seeps in. Then use your wrenches to try and loosen the parts. If they refuse to budge, hit them with another heavy dose of penetrating oil and again let them sit for several hours and try again.
Sometimes, very stubborn parts can be loosened if you apply heat to them. For example, a stuck nut that is warmed up with a heat gun will expand just enough to allow your wrench to turn it. However, don’t apply direct flame to parts that are still wet with oil. Penetrating oils will evaporate rather quickly, but remember that these are petroleum-based products, so there is the possibility of igniting them.
Other Types of Spray Lubricants
True penetrating oils aren’t the best product for every use and not every spray lubrication product is a penetrating oil.
Here are some of the other spray products available, along with their recommended uses:
Lithium Grease: This is a mixture of lithium hydroxide and petroleum oils. This is a true lubricant, not a penetrating oil, and it works well for lubricating parts where heavy loads or pressure is present, such as the hinges on heavy doors or mechanical cranks.
PTFE: This name stands forpolytetrafluoroethylene, but it really is just a Teflon spray. It is very good for lubricating chains and cables. It is a great material for lubricating parts on a bicycle.
Silicone: This is a spray lubricant containing about 1.5 percent silicone suspended in other materials to allow it to be applied as a spray. Silicone lubricants repel water and work well at extremely high or low temperatures. It is also unusual in that it can be used on rubber, wood, and plastic parts without staining them. It is not intended for applications where there will be heavy pressure.
Dry Lubricants: Although in spray form, dry lubricants come out damp, the solvents used to support the tiny, dry particles, usually graphite, quickly evaporate, leaving surfaces entirely dry. Dry lubricants are ideal for locks, indoor hinges, and drawer slides, since there is no oily mess and dirt doesn’t stick to them. Dry lubricants to not displace water, though, and they wear away fairly quickly and must be regularly reapplied.