Common Materials Used in Exhaust Hangers

The selection of material for exhaust hangers significantly impacts the exhaust system’s vibration dampening, alignment stability, and overall durability. Exhaust hangers must withstand a variety of mechanical stresses while resisting environmental and chemical degradation. Four primary materials dominate the market, each with distinct properties and chemical resistance profiles:

Rubber (Natural and Synthetic)

Rubber remains the most widely used material for exhaust hangers due to its excellent vibration absorption, flexibility, and relatively low cost. Natural rubber provides high resilience and elasticity but has limited resistance to oils, greases, ozone, and certain chemicals found in automotive environments. Exposure to these agents causes natural rubber to swell, crack, and eventually lose elasticity.

Synthetic rubbers offer improved chemical and weather resistance. For example, EPDM (ethylene propylene diene monomer) rubber is widely favored due to its excellent resistance to weathering, ozone, and moderate chemicals. However, EPDM still degrades when exposed to hydrocarbon-based fluids such as gasoline and motor oil. Another common synthetic rubber is nitrile rubber (NBR), which offers superior oil and fuel resistance but becomes less flexible at low temperatures, making it less ideal in cold climates.

Rubber hanger failures typically manifest as swelling, cracking, embrittlement, or loss of elasticity after prolonged contact with petroleum products, exhaust condensates, or road contaminants.

Steel (Carbon and Stainless)

Steel hangers, commonly fabricated from zinc-plated carbon steel or corrosion-resistant stainless steel (grades 304 and 316), are prized for their mechanical strength and high load-bearing capacity. Carbon steel hangers are prone to rust when exposed to moisture, deicing salts, and acidic exhaust gases, which can rapidly degrade their structural integrity.

Stainless steel hangers offer superior corrosion resistance due to their chromium content, which forms a protective oxide layer. However, they are not impervious; in chloride-rich environments such as winter road salt exposure, they can experience localized pitting and chloride-induced stress corrosion cracking, especially under tensile stress.

To mitigate corrosion, steel hangers are often coated with zinc plating, e-coats, or powder coatings that act as protective barriers. Nevertheless, any scratches or chips in the coating expose the underlying metal to corrosive elements, accelerating degradation.

Polyurethane

Polyurethane (PU) hangers strike a balance between flexibility, abrasion resistance, and chemical tolerance. They exhibit better resistance to oil, grease, and fuel compared to natural rubber and can tolerate a wider temperature range. However, polyurethane is susceptible to hydrolysis—the breakdown of polymer chains in hot, humid, and acidic environments—leading to embrittlement and loss of mechanical properties over time.

The hardness (durometer) of polyurethane affects its performance: softer grades provide excellent vibration damping but may absorb solvents and swell; harder grades maintain dimensional stability but transmit more vibration. Because of their chemical resistance and durability, polyurethane hangers are often used in off-road vehicles and heavy-duty applications where exposure to harsh chemicals is common.

Silicone

Silicone elastomers are distinguished by exceptional thermal stability and broad chemical inertness. They can withstand continuous temperatures up to 250°C (482°F) and intermittent peaks above 300°C (572°F), making them ideal for high-performance or turbocharged vehicles with hotter exhaust gases.

Silicone rubber resists oils, solvents, ozone, ultraviolet radiation, and most automotive chemicals better than organic rubbers. However, silicone typically has lower tear strength and can be more expensive, limiting its use primarily to specialized applications.

Its main chemical vulnerability lies in exposure to concentrated acids and alkalis, which are uncommon in automotive exhaust systems. Thus, silicone is a premium choice for durability and chemical resistance in demanding environments.

Chemical Exposure Mechanisms

A thorough understanding of how chemicals degrade exhaust hanger materials enables engineers to predict failures and select appropriate materials. The four primary chemical attack mechanisms are as follows:

Swelling and Plasticization

When a polymer absorbs a compatible chemical—such as oil or fuel into rubber—it swells and becomes softer, a process known as plasticization. This reduces the material’s modulus (stiffness) and load-bearing capacity, causing the hanger to sag and potentially allowing the exhaust system to contact the vehicle’s undercarriage.

Volumetric swelling exceeding 20% typically renders an exhaust hanger non-functional. The degree of swelling depends on the chemical’s compatibility with the polymer, concentration, temperature, and exposure duration. ASTM D471 is the standard test method used to measure volume changes in elastomers subjected to chemical immersion.

Plasticizer Extraction

Many rubber compounds contain plasticizers—low molecular weight substances added to maintain flexibility. Certain solvents, such as gasoline or brake cleaner, can leach these plasticizers out, causing the rubber to become brittle and prone to cracking under dynamic stresses. This plasticizer loss is often irreversible and accelerates with elevated temperature.

Oxidation and Ozone Attack

Oxygen and ozone (O3) attack unsaturated chemical bonds present in natural rubber and some synthetic rubbers. This leads to chain scission and cross-linking reactions, resulting in surface crazing or weathering cracks. Exposure to heat and ultraviolet light exacerbates this degradation.

Materials with saturated polymer backbones, such as EPDM and silicone, show much greater resistance to ozone and oxidative attack, making them preferable for outdoor or industrial environments with elevated ozone levels.

Corrosion and Galvanic Action

Metallic hangers experience electrochemical corrosion when exposed to electrolytes like road salt brine or acidic exhaust condensate. In the presence of moisture and salts, steel can rapidly rust, compromising hanger integrity.

Galvanic corrosion also occurs when dissimilar metals (e.g., stainless steel hanger in contact with carbon steel exhaust pipe) are electrically connected in the presence of an electrolyte, accelerating corrosion of the more anodic metal.

Proper isolation using rubber or polymer isolators between metal components is essential to minimize galvanic corrosion and prolong the life of metal hangers.

Specific Chemical Effects on Hanger Materials

The table below conceptually summarizes typical chemical threats and their effects on common exhaust hanger materials. Actual performance varies depending on chemical concentration, temperature, exposure time, and material formulation.

  • Motor Oil and Grease: Cause swelling and plasticization of natural rubber and EPDM, leading to loss of elasticity and mechanical strength. Polyurethane and silicone exhibit minimal volume change and maintain better mechanical properties. Steel hangers are chemically unaffected but can accumulate oil films that trap dirt and accelerate rust formation.
  • Road Salt (Sodium Chloride, Calcium Chloride): Elastomers are generally unaffected by salt, but salt solutions drastically accelerate corrosion of carbon steel hangers. Stainless steel, especially grade 316, resists salt-induced corrosion well but can experience localized pitting if its protective oxide layer is scratched. Salt increases moisture conductivity on surfaces, promoting galvanic corrosion currents.
  • Exhaust Fumes and Condensate: Exhaust gases contain acidic components such as sulfuric acid (from sulfur in fuel) and nitric acid (from combustion nitrogen oxides). These acids chemically attack rubber and polyurethane, causing surface degradation, embrittlement, and eventual cracking. Silicone resists acidic attack better than other polymers. Acidic condensate also corrodes steel hangers, particularly during short trips where the exhaust system does not reach sufficient temperature to evaporate moisture.
  • Industrial Pollutants (Sulfur Dioxide, Nitrogen Oxides, Ozone): In urban or industrial environments, airborne pollutants accelerate oxidation of natural rubber and styrene-butadiene rubber (SBR), leading to surface cracking and degradation. Ozone levels often correlate with UV radiation, exacerbating damage in unprotected rubber. EPDM and silicone are recommended in such environments due to their superior resistance.
  • Fuel and Solvents (Gasoline, Diesel, Methanol, Ethanol): Direct contact with fuel causes catastrophic swelling in natural rubber and EPDM, compromising mechanical integrity. Polyurethane and nitrile rubber provide moderate resistance, while silicone performs excellently. However, high-ethanol fuels (e.g., E85) can degrade certain silicone formulations, so material certification is critical. Steel hangers are chemically stable against fuel but may suffer corrosion from water-alcohol mixtures.

Selecting the Right Material for Your Environment

Choosing the appropriate exhaust hanger material requires a balanced evaluation of four primary factors: chemical exposure profile, operating temperature range, mechanical load (both static and dynamic), and cost constraints. The following considerations help guide material selection for specific applications:

High-Temperature Environments (Turbocharged, Performance, or Heavy-Duty Vehicles)

Exhaust temperatures in performance or heavy-duty applications frequently exceed 150°C (302°F), quickly degrading organic rubbers. Silicone hangers are the industry standard for these conditions, capable of continuous operation up to 250°C (482°F) and intermittent peaks above 300°C (572°F). Some specialty polyurethane formulations can tolerate up to 120°C (248°F) but are generally insufficient for high-performance applications.

Steel hangers inherently tolerate high temperatures but require corrosion protection to maintain longevity in harsh environments.

Cold Climate and Road Salt Exposure

Vehicles operating in northern climates face significant challenges due to subzero temperatures and frequent use of deicing salts. In these conditions, stainless steel hangers (grades 304 or 316) provide superior corrosion resistance compared to carbon steel. To prevent cracking in cold temperatures and damage from salt spray, rubber isolators should be EPDM or silicone, as natural rubber becomes brittle and deteriorates quickly.

Polyurethane is also a viable option when the durometer is selected to retain flexibility at temperatures as low as -40°C (-40°F).

Chemical Plant or Industrial Fleet Applications

Vehicles operating near chemical processing plants, refineries, or waste treatment facilities face extreme chemical exposures, including acids, solvents, and pollutants. Silicone hangers combined with stainless steel brackets provide the broadest chemical resistance and are recommended for these environments.

For less aggressive settings, EPDM or polyurethane may suffice. It is critical to verify chemical compatibility using manufacturer-provided data sheets or compatibility charts, such as the Parker O-Ring Handbook.

General Passenger Vehicles (OEM Replacement)

Most original equipment exhaust hangers utilize EPDM rubber or blends that balance cost, vibration damping, and durability under typical driving conditions. In moderate climates with minimal chemical exposure, EPDM hangers generally provide 5 to 10 years of service.

Upgrading to silicone or polyurethane hangers is often unnecessary unless premature failures occur due to environmental conditions or chemical exposure.

Protective Measures and Maintenance

Even the most chemically resistant materials can fail prematurely without proper protective measures and maintenance. Implementing these strategies extends hanger service life and reduces downtime:

Protective Coatings and Linings

Steel hangers benefit from protective coatings such as zinc plating, electrocoating (e-coat), PTFE (Teflon), or ceramic coatings. Zinc plating offers sacrificial protection at scratches, while e-coat provides uniform coverage but can be damaged by mechanical impacts. PTFE coatings reduce friction and chemical adhesion, facilitating the cleaning of contaminants. Ceramic coatings excel in high-temperature zones but are more expensive.

Elastomeric hangers can sometimes be over-molded with a thin fluoropolymer layer, enhancing chemical resistance, though this increases manufacturing costs.

Regular Inspection and Cleaning

Routine maintenance inspections are crucial to detect early signs of hanger degradation. Inspect for swelling, cracking, corrosion, or coating damage. If oil or grease accumulates on rubber hangers, clean with mild solvents like isopropyl alcohol instead of aggressive chemicals such as gasoline.

Metal hangers should be checked for rust and any coating breaches. Fleets operating in high-corrosion environments often adopt a 6-month inspection interval to proactively mitigate failures.

Proper Installation and Alignment

Misalignment of the exhaust system imposes tensile and torsional stresses on hangers, increasing the likelihood of mechanical failure and chemical degradation. Ensuring proper installation, with hanger brackets allowing free movement while securely supporting the exhaust weight, is critical.

Rubber isolators should be used to electrically isolate steel components and prevent galvanic corrosion. Replace any hangers showing visible damage promptly to avoid cascading system failures.

Material Upgrades and Retrofits

When original hangers fail prematurely, upgrading the material can significantly extend service life. For example, switching from natural rubber to EPDM or silicone in environments with oil or chemical exposure can triple hanger longevity. Retrofitting carbon steel brackets with stainless steel alternatives eliminates rust-related failures.

Although material upgrades may increase unit costs ($5–20 per hanger), the investment is modest compared to labor costs and downtime associated with exhaust system repairs.

Real-World Case Studies

Two case studies illustrate the critical importance of material selection and maintenance in real-world fleet operations:

Case Study 1: Municipal Snowplow Fleet

A municipal fleet operating snowplow trucks in a northern city experienced chronic exhaust hanger failures during winter months. The original hangers, made from natural rubber and carbon steel brackets, consistently cracked and corroded within a single season. Investigation revealed that exposure to calcium chloride brine used for road deicing was the primary cause.

The fleet replaced the hangers with silicone isolators paired with stainless steel brackets. This upgrade extended hanger life to over three years, significantly reducing maintenance downtime. The initial cost increase of approximately $15 per vehicle was recovered within the first year through reduced labor and parts replacement expenses.

Case Study 2: Automotive Test Fleet in Industrial Zone

An automotive manufacturer’s test fleet operating near a chemical refinery suffered premature failures of exhaust hangers, primarily due to exposure to acidic exhaust condensate mixed with industrial pollutants.

Original EPDM rubber hangers exhibited rapid embrittlement and cracking, while carbon steel brackets corroded quickly. The fleet switched to silicone hangers and stainless steel brackets, which resisted the acidic environment effectively. The retrofit resulted in a 50% increase in hanger service life and improved vehicle uptime.

Conclusion

The chemical environment surrounding an exhaust system plays a pivotal role in the performance and longevity of exhaust hangers. Material selection must consider chemical exposure, operating temperature, mechanical stresses, and cost to ensure optimal durability.

Rubber materials remain common for their vibration damping but vary widely in chemical resistance. Steel provides mechanical strength but requires corrosion protection, especially in chloride-rich environments. Polyurethane offers chemical and abrasion resistance for demanding applications, while silicone delivers superior high-temperature and chemical resilience for performance vehicles and harsh environments.

Implementing protective coatings, regular inspections, proper installation, and material upgrades can substantially extend hanger life, reduce maintenance costs, and improve fleet reliability. Real-world examples underscore the value of tailoring exhaust hanger materials to specific environmental challenges.