Dielectric Grease: What It Is & How to Use It

Dielectric grease, or tune-up grease, is a silicone-based grease that repels moisture and protects electrical connections against corrosion. It is also used to keep dirt, water, and other elements out of electrical connections. It has many uses, including automotive tune-ups, home electrical work, and recreational vehicle wiring.

Dielectric grease does not dissolve in most liquids, so it is good for marine and outdoor applications. You can use this grease to lubricate the rubber parts of electrical connectors, spark plug wires, and to protect electrical connections on your boat or recreational vehicle from corrosion. Since dielectric grease is a silicone grease, it should not be used on silicone-based rubbers or plastics, as it will break them down over time. The grease does not conduct electricity, so it shouldn’t be applied directly to the mating surfaces (pins and sockets) of an electrical connection.

What is Dielectric Grease Made Of?

Dielectric grease is made of two primary components: a silicone base and a thickener. The silicone base gives it its waterproofing and insulating properties, while the thickener gives it the viscosity needed to stay in place once applied. It typically appears as a translucent, milky white gel. Unlike petroleum-based greases, it doesn’t break down rubber or most plastics.

Dielectric Grease vs. Lubricating Grease: What’s the Difference?

These two products are not interchangeable, and using one in place of the other can cause problems. Lubricating grease is formulated from lubricating oil, a thickener, and performance additives. It’s designed to reduce friction between moving metal parts, typically applied through Zerk fittings in automotive and industrial machinery.

Dielectric grease serves a different purpose entirely. It’s not a lubricant for moving parts. Its job is to seal electrical connections from moisture and corrosion, insulate against voltage leakage, and prevent arcing, particularly in high-voltage applications like spark plug boots. If you need to lubricate a wheel bearing, reach for the right bearing grease. If you’re working on electrical connections, that’s where dielectric grease belongs.

Benefits of Dielectric Grease

When applied correctly, dielectric grease:

• Prevents moisture from entering electrical connections
• Protects against corrosion on terminals and contacts
• Insulates against voltage leakage and arcing
• Withstands temperature extremes without hardening, melting, or drying out
• Keeps rubber gaskets and boots pliable over time
• Makes connectors easier to slide together and pull apart
• Does not harm rubber or most plastics when used as directed

Will Dielectric Grease Cause a Connection to Fail?

This is a common concern, and the short answer is no, when applied correctly. Because dielectric grease is non-conductive, there’s a widespread belief that getting it into a connector will interrupt the electrical connection. In practice, the metal contacts are tight enough to displace the grease on contact, maintaining the connection while the grease seals the surrounding area from moisture and contamination.

The important qualifier is “when applied correctly.” You should never pack a connector full of grease or squirt large amounts into the mating surfaces. A thin, even application on the outer housing, gasket, or boot is all that’s needed. The grease does its job at the perimeter, not between the contacts.

How to Apply Dielectric Grease

To use dielectric grease during an automotive tune-up on a gasoline or diesel engine, apply a bit of the grease to the end of the rubber boot on a spark plug wire and spread it around so it is just covering the inside of the lip. This will prevent high voltage electricity from traveling inside the boot and “leaking” out into the engine block. Additionally, the dielectric grease will make it easier to slide the boot over the ceramic insulator on the spark plug and ensure that there is a water-tight seal around the plug that will protect the connection from water and dirt.

You can also apply dielectric grease to the gaskets on multi-pin connectors that are typical in the electrical systems of boats and recreational vehicles. Simply take a small dab of the grease and smear it around the gasket on both sides (if possible) before inserting the gasket around the connection.

Dielectric grease can also be applied to the metal parts of virtually any electrical connection that will be exposed to the elements to serve as a sealant that protects the connection from contamination and corrosion. This should be done very carefully, as the grease will cut off the flow of electricity through the connection if some of it is left between the mating surfaces. As always, we recommend working with your local auto mechanic when doing any maintenance on your vehicle.

You can find more tips and information for automobile maintenance on Blain’s Farm & Fleet’s Automotive blog.

Frequently Asked Questions

What should you not use dielectric grease on?

Situations where it doesn’t belong: directly on the metal contact surfaces of electrical connectors, the pins and sockets where current actually flows, and on silicone-based rubber or plastics. Applied to metal contacts, the grease can interrupt the electrical connection and cause failure. Applied to silicone materials, it can break them down over time. Stick to the outer housing, gaskets, boots, and ceramic surfaces, and you’ll avoid both problems.

Can I use regular grease in place of dielectric grease? 

No. Regular lubricating grease and dielectric grease are formulated for completely different jobs. Lubricating grease is designed to reduce friction between moving metal parts and is not safe for electrical connections; it can conduct electricity or corrode the surrounding materials. Dielectric grease is specifically formulated to insulate, seal, and protect electrical connections from moisture and corrosion without interfering with conductivity when applied correctly. Using one in place of the other is likely to cause more problems than it solves.

Can too much dielectric grease cause problems? 

Yes. Applying too much increases the risk of the grease migrating onto the metal contact surfaces, where it can disrupt the electrical connection and cause misfires or connection failures. A thin, even coat is all that’s needed for any application; more doesn’t improve protection and just creates unnecessary risk. If you’ve overapplied, clean the excess with a contact cleaner or petroleum distillate before reassembling.

How long will dielectric grease last? 

Dielectric grease is temperature stable and doesn’t dry out, harden, or evaporate under normal conditions, so it tends to last a long time once applied, often for the life of the component it’s protecting. The silicone base resists breakdown from heat, cold, and moisture, which is what makes it reliable for automotive applications that see significant temperature swings.