Here’s How To Use Silicone Sealant or RTV

What's cool about much of it is it's transferable across a wide assortment of vehicles, and heck, even into non-automotive arenas. One of these core competencies is properly using silicone sealant, more widely known as RTV.

Knowing when and how to use silicone sealant, as well as selecting the right type, will ensure your car's crucial systems will be properly sealed up and not leak out important fluids like engine oil, coolant, gear and differential oil, and more. So let’s talk about how to properly use silicone sealant and ensure you've not only properly sealed two components, but that you haven't used too much of it in the process.

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While silicone sealant is generally considered far from harmful, it's a good idea to keep these few safety precautions in mind.

The beauty of silicone sealant is it really doesn't require anything beyond the tube of the substance itself and a steady hand. 

It’s also a good idea to do your sealing on a steady, stable surface. This could be a small foldable workbench, work table, or even your driveway. Make sure you're out of the wind and uninterrupted by any four-legged friends, as you don't want to pick out leaves or re-shape paw imprints after carefully laying down a nice, uniform bead of RTV.

As far as which sealant to use, there are many options from several brands out there, all with good reviews. Just make sure that the one you purchase works with your application, such as a formula that's meant for sealing automatic transmissions, one that stands up to heat, or one that's meant for exterior application. 

For the application in our photos, we used Victor Reinz Reinzosil because it's a well-rated, high-temperature, and fast-curing universal silicone sealant.

Here are all the steps in successfully sealing some surfaces with silicone!

Start by prepping the mating surfaces. If you're resealing something that was last sealed from the factory, taking a look at how much sealant was initially used can help cue you in on how thick of a bead to lay down.

Use brake cleaner and a rag to make them nice’n clean, and the brass brush can be used to scrape away any old sealant or debris. The reason for the brush having brass bristles is it won't damage the mating surface and disallow a good seal. Make sure that there's no leftover film from any cleaning agents.

Next up is to steady your hand and lay down a bead of sealant. Some folks apply a bead to both surfaces, and some only one. You also don't want to lay down too much as properly cured and torqued-down sealant makes a better seal than most people might think.

A good default thickness is 1/8th of an inch. Keep the sealant away from the inner edge of what you're sealing, unless the application calls for a particularly thin bead. You don't want it entering where fluids are moving around once torqued down, allowing it to break off and potentially clog up crucial components like oil pickups. Still, some applications call for thicker beads, research what is best for your particular car's components.

In our instance, we kept a thin bead somewhat close to the inner edge, as that's where the factory bead was laid. Otherwise, it's a good idea to lay the bead more towards the middle and only come in close to the inner edge when there's a bolt hole to seal off.

Ensure that the bead is a uniform thickness all over, and be sure to stay on the inside of bolt holes. For added peace of mind, if there's enough of a lip on the mating surface, it's not a bad idea to loop the bead around the bolt holes.

Check out your chosen sealant's instructions to see what its cure time is. Some require letting it sit, unjoined, for a period of time before snugging it up to what you're sealing. 

Some sealants are anaerobic, meaning they won't cure until they experience an absence of air. Others require you to join the two surfaces, but only tighten the bolts finger-tight and let it sit for a period of time before torquing them down. 

So pay attention to the instructions.

Next, carefully line up the bolt holes, and lightly thread in one bolt before letting go of them. Quickly follow up with other bolts, but just finger-tight. 

Remember to then be mindful of each brand/type of silicone sealant's cure time, and proceed as necessary with either letting it sit or torquing it down to the manufacturer's recommended torque setting.

Some sealants may require they sit for a period of time before experiencing any amount of heat or fluids passing by them. Again, be sure to read your chosen sealant's directions.

YouTube DIY Authority and proud New Jersey Car Nut, Chris Fix, made an excellent video on how to use silicone sealant.