How To Replace Traditional Gaskets with Chemical Gaskets

If you can't locate a ready-made pre-cut gasket, chemical gasket makers can easily get you out of a bind.

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Vehicle power trains have drastically evolved since their invention, especially over the past two decades. New, tougher additives in oil and anti-freeze help keep your vehicle running longer and reduce maintenance costs, but require innovative gasketing solutions to eliminate leaks.

In today’s vehicles, room temperature vulcanizing (RTV) chemical-based form-in-place gasket makers have replaced time-honored pre-cut gaskets throughout.

Even pros had issues with so-called “come-backs” when RTVs were introduced. However, once they learned the correct cleaning procedures and installation processes, along with identifying the right RTV for the application and what tools to use, RTV gasket makers became second nature.

Here’s what you need to know to do the job right the first time.

How To Choose the Right Chemical Gasket

RTVs have different characteristics that coincide with specific applications. Choose the right RTV for the job to avoid leaks.

Here are the three most commonly used form-in-place RTV gaskets makers:

  • For stamped metal parts with flanges, such as oil and transmission pans, valve covers, timing covers, differential covers and transfer cases, or parts made from composite materials, choose a flexible, oil-resistant form-in-place RTV. They’re unaffected by oil additives and remain flexible under all temperature conditions.
  • For more precisely machined parts or cooling system repairs, such as water pumps or thermostat housings, choose an RTV designed to stay rigid and resist vibration under high torque loads. This type of RTV also fills and seals gaps where a cut-gasket and rubber or silicone seal butt up against each other.
  • For exhaust manifolds or headers, and high temperature environments found in four-cylinder and turbocharged engines, choose a high temperature RTV resistant to aging, weathering, shrinking and cracking.

Note: Never use an RTV to replace a cylinder head gasket.

Removing Old Gasket Material

It’s critical to remove even the smallest slivers of an old gasket or RTV. Any residue left behind can cause gaps between sealing/mating surfaces or uneven part alignment, compromising seal integrity and assembly operation.

Remove old gasketing materials with these items:

Never use a metal razor blade or hard wire brush on sealing/mating surfaces because they can scratch or gouge them.

Skip your high-speed drill with abrasive pads or conditioning discs as well. They can quickly mar surfaces, especially parts made of soft aluminum, and the grit produced by the pads is finer than an oil filter can trap. Once inside an engine, the coarse bits can damage engine bearings or the engine block.

How To Properly Prepare Surfaces

Sealing/mating surfaces must be free of grease, dirt and grime as well as old gasket material. Although they look like gel or caulk, RTVs are technically a liquid adhesive. All surfaces need to be clean and dry for an RTV to correctly stick to the sealing surfaces, creating that foolproof, leakproof seal.

  • Carefully and completely remove the old gasket or RTV using the tools listed above.
  • On parts with grooves or channels, use a pick or non-scratch pad to totally remove any small specs of old RTV. New RTV will not adhere to old RTV.
  • If possible, thoroughly wash the parts with detergent and water and rinse with clean water.
  • Let dry or dry with lint-free shop rags or towels.
  • Spray both sealing surfaces with a chlorinated or non-chlorinated degreasing agent and allow to dry.

Applying Chemical Gasket Makers

This is a case of too much is NOT a good thing. Use as little RTV as possible to do the job. Applying too much can cause leaks.

  • On the cleaned/prepared surfaces, run a bead of RTV between an 1/8-in. and 1/4-in. wide over the entire sealing surface, completely encircling all bolt holes.
  • Install the part while the RTV is still wet. Do not let RTV “skin-over.”
  • Immediately, fully tighten the mounting/assembly bolts by hand.
  • Let the parts sit for one hour.
  • Torque all fasteners to spec in a star or crisscross pattern to distribute the clamping load, flattening the RTV evenly.
  • Standard silicone RTV can take up to 24 hours to fully cure.

Common Gasket Maker Mistakes

RTVs are extremely reliable and resistant to vibration, fluids and powerful additives, extreme temperature fluctuations and pressures — when used according to manufacturers’ instructions, that is. Here are common mistakes even skilled pros make that compromise a repair:

  • Surfaces not cleaned or prepared correctly;
  • Using the wrong RTV for your application;
  • Applying too much or not enough RTV;
  • Waiting for RTV to skin-over before reassembling;
  • Not allowing RTV to fully cure before adding fluids or returning to service;
  • Using RTV as a gasket dressing on traditional gaskets, or to hold rubber/synthetic gaskets in place. These gaskets must be installed dry.
  • Using RTV on an application exposed to gasoline. Use a solvent-based product instead.
  • Using RTV to replace or dress a cylinder head gasket.

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Bob Lacivita
Bob Lacivita is an award-winning ASE and General Motors auto technician, educator and freelance writer who has written about DIY car repairs and vehicle maintenance topics. His work has been featured in The Family Handyman, a Reader's Digest book and Classic Bike Rider magazine. He has been a career and technical educator for 25 years teaching automotive technology, as well as writing state, federal and organizational foundation grants. He also helped design a unique curriculum delivery model that integrates rigorous, relevant academic standards seamlessly into career and technical education.