Dielectric grease is a non-conductive, silicone-based grease that's designed to seal out moisture and prevent corrosion on electrical connectors. It also disrupts the flow of electrical current, which makes it good for lubricating and sealing the rubber parts of electrical connectors. It's commonly used in automotive spark plug wires, recreational and utility vehicles, and electrical systems in aircraft.
This material is a translucent, gray lubricant that does not dissolve in liquids like ethanol, methanol, mineral oil, and water. It can be dissolved with Methyl Ethyl Ketone (MEK) and mineral spirits though. Dielectric grease affects silicone rubber over time, so it isn't always a good choice to use it on silicone-based O-rings or wiring harnesses.
It can withstand high temperatures, making it a good choice for engine compartments and similar locations. Many dielectric greases are rated to work in up to 392° F (200° C) temperatures, and some can operate at up to 500° F (260° C). Though there are other greases that can work at these temperatures, they may not prevent the flow of electrical current like dielectric grease does.
Dielectric grease is widely used as a sealant for spark plugs in gasoline or diesel engines, as well as on the gaskets of multi-pin connectors in the electrical systems of vehicles and boats. When used with spark plugs, it's applied to the rubber part of the plug wire. This helps the boot slide onto the plug's ceramic insulator and keeps dirt or moisture from contaminating the seal and disrupting the electrical current.
Besides being used to seal rubber covers on electrical connections, dielectric grease also prevents corrosion when applied directly to metal connectors. Though it works well for this purpose, it can sometimes cause a connection to stop working if not all of the grease is pushed out of the way between the points of contact inside the connector. Additionally, it is often used to lubricate other engine-related parts, like rotors, distributor caps, and speedometer cables. It can be used in other situations where electrical connections may be exposed to moisture and dirt as well, like outdoor lights, satellite TV installations, trailer hitch wiring, and battery terminals.
Silicone-based lubricants, including dielectric grease, can irritate the skin and eyes, so users should wear safety glasses and gloves when using it, and should wash any skin or clothes that come into contact with it promptly. At high temperatures, it may create formaldehyde, which irritates the eyes and respiratory system, and is associated with cancer. Those buying this product should consider the temperature conditions in which they need it to work, since some formulations are better for higher temperatures than others.
Grease and lubricants in general can ignite and burn when they're exposed to a lot of oxygen. This is a particular risk when they are used in medical devices, pressurized air systems, or oxygen systems in aircraft. This type of grease should never be applied to the threads of oxygen cylinders or valves used on oxygen systems, since the rapid reaction between it and the oxygen could cause an explosion or fire. In addition, most greases can affect paint and coatings on machines or vehicles if left on for a long time. Any excess product should be cleaned up, including any that's spilled on floors, to prevent a slipping hazard.