What is Dielectric Grease & Why (& Where) Should You Use It?

Pop open any old tune-up manual and you’re bound to find mention of something called dielectric grease. In fact, a lot of experienced mechanics simply call dielectric grease “tune up grease” for that very reason. But even though it’s often associated with old-school maintenance routines, it is still plenty useful in modern vehicles as well.

In fact, with the increasing role of computers and sensors in cars and trucks nowadays, dielectric grease is really, really important. And it’ll likely stay that way for a long time, considering the current trajectory of electric vehicle adoption.

What is Dielectric Grease?

Technically, dielectric grease is considered a lubricant. But lubrication is only part of the benefits of a good tune up grease. That’s because “dielectric” is a fancy way of saying it won’t conduct electricity. Or in other words, it’s essentially an electrical insulator in fluid form.

So dielectric grease is often found around electrical systems, where it can be used to lubricate connectors, seal gaps, and thwart corrosion by preventing moisture ingress. Better still, dielectric grease can typically withstand extreme heat cycles, which makes it a smart choice to stop plastic and rubber parts from fusing together in high-temperature environments, like, say, in an engine bay.

All those reasons meant that, back in the day, applying a dielectric grease on ignition terminals, distributor caps, and in spark plug boots was one of the most important aspects of a regular vehicle tune up, hence why dielectric grease is often called “tune up grease.”

Tune Up Grease Is Still Useful Today

Since dielectric grease is both an electrical insulator and a lubricant, it has a ton of uses in a modern vehicle. It mitigates electrical shorts across connector pins, keeps rubber parts from drying out, and coats dissimilar metals to prevent seizing.

Conversely, if you’ve ever had to unplug an ancient electrical connector, only to find it’s fused tight inside the opposite receptacle, then you know how helpful a little dab of dielectric grease can be when assembling (and disassembling) components.

But note that we said “dab” right there. Knowing how much dielectric grease to apply is critical, as too much can actually prevent a good electrical connection. In most cases, a small layer of grease is all you’ll need, particularly if you’re using it on a precise electrical component like a sensor connector or ECU port.

Here’s another good tip: While it’s common in the automotive world, dielectric grease can be handy around the house too, from coax cable to washing machine knobs. And it’s not that expensive either, so it makes a lot of sense to buy a small tube for a few bucks, and toss it in your toolbox so it’s ready if/when you need it.

Five Good Automotive Uses for Dielectric Grease (& A Bonus One Too!)

Let’s talk specifics now. We put together a simple list of five handy applications for tune-up grease around your modern car, truck, or SUV.

1. Spark Plug Boots

Well, this is a no-brainer. As mentioned earlier, part of the reason folks call dielectric grease a “tune up” grease is because it was so valuable in ignition systems. And that holds true today. While you may not have a distributor anymore, a dab of dielectric grease on the spark plug body can prevent the boots from fusing to the spark plugs, making them easier to pull off in the future.

2. Battery Terminals

This is another good one. Battery terminals have tendency to rust and corrode, which means that they can seize right to the battery posts. And the corrosion can also eat away at the retaining hardware (especially inside the threads), causing a lot of rounded 10mm nuts. Here’s an application where you can be a bit more liberal with the application of dielectric grease, as you want to make sure the tops of the posts and fastener heads/threads are well-covered.

3. Electrical Connectors

Just get in the habit of applying a little dab of dielectric grease to the connector body and socket every time you disconnect them. And if you’ve got a weatherproof connector with a rubber boot or grommet (like you’d see in a Deutsch or Weather Pack connector), coating the rubber with a thin film of grease can prevent it from fusing to the mating connector after about a jillion underhood heat cycles.

4. Headlight & Lamp Sockets

We don’t just mean the electrical connector here, either. Many modern bulb sockets have an integrated rubber gasket that seals the headlight housing once the lamp is locked into position. Again, a thin film of dielectric grease can prevent that gasket from adhering itself to the back of the housing. Honestly, any bulb can probably benefit from a small dab of grease to make them easy to remove later.

5. Fuse Boxes

If you’ve got an external fuse box or standalone fuse blocks for some extra electrical accessories, then putting a bead of dielectric grease around its latches and seams can work wonders in keeping off-road grit and moisture out. Or, if your fuse box is really crowded, a tiny (tiny!) application of tune-up grease on the fuse blades can save a lot of frustration, especially if you have to use one of those plastic fuse tweezer tools to pluck them out.

Bonus! Sealing Lids & Panels

Remember, one of the main uses for dielectric grease used to be sealing the distributor cap cover to keep dust and moisture out. So, even on non-automotive applications, if you want to keep grit or rainwater out of an enclosure without an airtight seal, then a dollop of dielectric grease can do the trick. (It’s handy for other household jobs too, like sealing landscape lighting or junction boxes.) Dielectric grease is relatively easy to clean up as well, making it a far better choice for the job than a traditional all-purpose grease.

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Got any other clever uses for dielectric grease? Did we miss a common application? Let us know in the comments!