Here’s How To Use Silicone Sealant or RTV

Don’t have cold feet, use RTV with glee!

byPeter Nelson| PUBLISHED Nov 11, 2022 2:00 PM
Here’s How To Use Silicone Sealant or RTV
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Do-it-yourself maintenance is an endless list of learning the basics. From lifting up and supporting a car to general engine maintenance, there's always a first attempt that builds up competency and confidence. These then prepare you for more simple-yet-crucial jobs that eventually turn into muscle memory.

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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Silicone Sealant Safety

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

  • Nitrile latex gloves to keep from making a mess on your hands
  • Eye protection if you're applying it in tight spaces or underneath the car—nobody likes dirt falling in their eyes while carefully attaching an oil pan to their car's engine, or accidentally getting brake cleaner in your eye
  • A mask or respirator if you're prepping the surface with harmful chemicals

Everything You’ll Need to Use Silicone Sealant

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

Materials

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.

Peter Nelson

Here’s How To Use Silicone Sealant

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

1. Prep the Surfaces

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.

2. Start Laying the Bead

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.

3. Ensure Bead Uniformity and Pay Close Attention to Bolt Holes

Peter Nelson

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.

4. Follow Cure Time Procedures

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.

5. Join the Surfaces

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.

6. Be Cognisant of Full Sealing Time

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.

Video 

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

Quick Tips

  • Silicone sealant should almost never be used where a paper, cork, metallic, or rubber gasket is intended. For instance, it shouldn't replace a cylinder head gasket or a rubber oil pan gasket that the manufacturer requires. Always follow the manufacturer's instructions.
  • For certain applications, a rubber, paper, cork, or metallic gasket might no longer be produced, in which case do your research to find out which silicone sealant and application strategy is best.
  • There's no shame in re-applying if you lay down a bead and aren't happy with how uniform it looks. Sealant is cheap, but chunks of it potentially breaking off and entering the engine's oil pickup isn't.
  • Ensure the sealant you're using is approved for its intended location. Be mindful of heat rating, as well as if it will stand up to the fluid it's sealing.
  • Only use dedicated thread sealer on sealing hardware.

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