Other Articles - January/February - 2022

Stopping That Leak – Sealing Technology

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One of the most frustrating things about repairing vehicles is when you receive a call regarding that small puddle/spot of oil, fluid, or antifreeze the owner found on their garage floor after your repair.

Forty years ago, sealing technology was pretty standard across the industry, with gaskets or rubber seals being the predominant sealing solutions used by the OEM’s. Today a lot has changed. With many applications, gaskets have been replaced by flexible sealers. Flexible sealer (gasket maker) technology has made giant strides, with specialized sealers being developed for each specific component application.


Sealers were introduced in the 1930s by Permatex with the introduction of “Form a Gasket” In the 1980’s we all remember the introduction of the “Blue RTV (Room Temperature Vulcanizing) silicone sealers.” Those sealers were thought to be miracle products at the time. As vehicles continued to change, so have the sealers. Sealing today’s vehicle components with the old technologies many times leads to leak issues as the component materials and the chemicals used in today’s powertrains have made major changes. Three types of sealers are common in the marketplace to meet the different sealing challenges:

  • Aerobic (RTV) cures with exposure to moisture in the atmosphere
  • Anaerobic cures when no oxygen is present
  • Solvent evaporative cures as the sealer solvents evaporate

Antifreeze, Transmission Fluid and Engine Oil are not the same products they were just a few years ago. Ethelene glycol (green) antifreeze has not been used by any manufacture since the early 2000s. We now have antifreeze that needs to meet manufacture specific requirements. The design of the antifreeze has changed dramatically in the past few years with the introduction of OAT, HOAT, IAT, NOAT, SiOAT, PHOAT, and Glysatin antifreeze designs, which are common in today’s vehicles. As I covered in-depth in a previous Gears article, “Cool It,” it is critical that the correct antifreeze be used in the vehicle you are servicing.

Engine oils and transmission fluids have undergone the same type of evolution, with more than 600 brands of engine oil being available worldwide. Many of those oils contain different additive packages, which as with different coolant additive packages, they may react with the sealer that you are using.

Component materials have also changed with time. Decades ago, most components were made of cast iron. Today we see plastics, aluminum, and magnesium is used in many powertrain components. Intermixing of the different component materials provides a major challenge as the expansion/contraction rate of plastic versus aluminum is totally different. Widespread use of turbochargers and superchargers on many of today’s vehicles makes sealing the power train components even more of a challenge.

Today, only 1/3 of components are sealed using a gasket, 1/3 are sealed with a flexible sealer, and 1/3 use a gasket and some form of adhesive sealer.

Precut gaskets and flexible sealers have different advantages and disadvantages (Table 1).

In the last few years, flexible sealers have made major strides. As an example, Permatex, the world’s largest supplier of sealers, now has products that will fully cure for use in one minute. The older design sealers had limits on which components they could be used on. As an example, you would never want to use silicone to seal a surface exposed to gasoline. Today, manufactures have multiple different sealers, including products to seal surfaces exposed to gasoline.

So how does one know which sealer to use with so many different types are available? Numerous companies sell RTV-type sealers. Since many shops use Permatex products, we will use their product line to show which sealer is used for each application. A few years ago, Permatex added color codes to their different usage sealers. Black, Grey, and Red silicone sealers are the most popular. Each color designates the type of use the sealer was designed for. This type of color-coding has carried through to other companies as well (Figure 1).

Black: Black RTV was designed for flexibility and oil resistance. Common uses are oil pans, transmission pans, extension housings, and timing covers. Black is the most flexible of the three common sealers. The typical temperature range for the black RTV sealers is -65 to 500 F.

Gray: Gray RTV was designed to cure as a “ridged seal” so that torque values can be maintained. Gray sealer has the highest load-carrying capability. The gray sealer has replaced the black and blue RTV products for most newer vehicle applications. Common uses are intake manifold end seals, thermostat housings, water pumps, and valve covers. The temperature range for this sealer varies depending on which gray version is used and the brand of sealer you purchase. Typically, it ranges between -65/–75 up to 450/700 F.

Red: Red RTV was designed for high-temperature use. Red sealers resist thermal cycling. Common uses are headers, exhaust manifolds, exhaust systems, and turbochargers. Like the gray RTV, the red sealer, temperature range will vary from -65/- 75 up to 650/750 F depending on the sealer purchased.


RTV sealers are designated as “Anaerobic” sealers meaning that they cure when exposed to moisture in our planet’s atmosphere. They are NOT designed to seal a finely machined tight-fitting connection without exposure to oxygen (Figure 2).

“Anaerobic” sealers are designed for those finally machined mating parts with a 0.015” or smaller gap between the parts. Anaerobic sealer typically looks like jam and cures only when oxygen is no longer present. Some transmission parts and many engine parts, such as the Porsche/VW engine case halves, as well as some motorcycle engine parts, require an anaerobic sealer.

Typical silicone sealers are great for general use but there as some applications that you may need a more refined sealer to properly seal the parts.

Fuel tanks, fuel systems:

A new sealer was introduced to seal areas exposed to gasoline. Permatex #29132 is a “Hypalon” design sealer made of synthetic rubber, which cures by solvent evaporation.

Water pumps, Thermostat housings:

A new sealer was developed due to the new coolants being used in today’s vehicles. Permatex # 22071 is designed to withstand silicates, organic acids, and nitrates found in modern coolants.

Rear axles:

Newer rear axle fluids develop a lot of acids during operation. The gear oil will attack common RTV-type sealers over time, leading to seepage issues. Permatex #81182 is designed with additives that prevent the acids from degrading the quality of the seal.

Automatic Transmissions:

Synthetic transmission fluids, as well as the friction modifiers and detergents used in some ATF, can attack some conventional RTV sealers. Permatex #81180 is designed to seal when either conventional or synthetic fluid is used.


Silicone sealers/gasket makers had a major issue in the early days, as you needed to leave the vehicle sit typically overnight before it was filled with fluid in order to allow the sealer to fully cure. Even now, some of the sealers require 8 hours or more to fully cure. In the last couple of years, sealers were introduced that cure in 90 minutes, some as fast as 1 minute. So, what is the difference? Typically, from your perspective, it is price. The faster the cure time, the more expensive the sealer.

  1. Issues to be aware of when using a gasket maker/sealer product
  2. Never use a gasket maker/sealer to replace a head gasket.
  3. Using the wrong type of gasket maker/sealer for your application can lead to leakage issues.
  4. Applying too much gasket maker can lead to component failure as it can plug filters and pump pickups. A thin film of sealer is all that is needed.
  5. Never use an RTV or anaerobic sealers on an application that is exposed to gasoline.
  6. Always allow the full cure time before returning the vehicle to service.
  7. Never try to fill a large gap with an anaerobic gasket maker.
  8. Incomplete surface preparation. The surface must be free of all oil, dirt, antifreeze, and other contaminants.
  9. Incorrect reassembly. Some products are designed to be fully torqued upon assembly, while other manufactures want the bolts tightened until the sealer starts to deform. The sealer is then allowed to cure for 1-2 hours, then the bolts are tightened and an additional to turn.
  10. Gasket makers are not designed to act as a dressing on a conventional gasket, especially cork gaskets.

Making a mistake when it comes to a sealer/gasket maker can cost you a lot of time and money, so research the product you want to use carefully. Sealers are an ever-changing technology with numerous different companies offering the products such as Loctite, Permatex, JB, as well as the OEM’s such as GM, Ford, and Chrysler. As you can see, which product you choose needs to be based on what you are trying to seal as well as how much cure time you would like to allow.

A special thanks to the chemists and application engineers from Permatex for the information they shared for this article. Until next time remember: “Good cars get you from point A to point B. Great cars, well… they just get you into trouble.”