Rick's Free Auto Repair Advice

Dielectric grease

What is Dielectric grease?

Dielectric grease is used in automotive applications to prevent corrosion in electrical connections, lubricate rubber parts, and prevent spark plug boots from welding to spark plug porcelain. Dielectric grease is non-conductive, so when it’s applied to the inside of a spark plug boot dielectric grease it also helps prevent “tracking” where high voltage fires down the porcelain portion of the plug to the metal shell where the voltage finds ground.

What’s in dielectric grease?

Dielectric grease is made from a polydimethylsiloxane dielectric greasesilicone oil base (as opposed to a petroleum base) with a thickener and silicone dioxide.

What does dielectric grease do?

It lubricates without harming rubber materials. It prevents oxidation on electrical connections. It is NOT an electrical insulator (more on that later).

Dielectric grease is not thermal grease

Some ignition and radiator fan modules require a thin coating of thermal grease to dissipate heat away from the module to a heat sink metal area. Thermal grease often made from a silicone base but also includes heat-conducting metal powders to transfer heat away from the module. If an automotive application calls for thermal grease, you cannot use dielectric grease in place of thermal grease.

Where do you use dielectric grease in automotive applications?

• Spark plug boots to prevent the rubber from welding to the spark plug and to prevent tracking down the side of the plug.
• Lubrication for O-rings and water sealing silicone seals
• Electrical connectors to reduce terminal oxidation and fretting
• Bulb sockets to keep out water and prevent corrosion
• Trailer connectors
• General electrical connections
• General plastic or rubber lubrication

Does dielectric grease increase resistance in an electrical connection?

No. This is a myth and it’s based on a misunderstanding of how dielectric grease works in an electrical connector. When electrical connectors are mated, they establish a metal-to-metal contact. In other words, the grease is wiped away due to the spring tension of the connectors. The grease still surrounds the connection, preventing oxidation. But it does not add resistance to the circuit.

©, 2021 Rick Muscoplat

Posted on by Rick Muscoplat


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