Automotive silicone parts are subjected to some of the most challenging environments in a vehicle — high temperature under the vehicle hood, continuous exposure to oils and coolants, and years of vibration and aging. These components provide reliable performance, maintain sealing integrity and full adherence to the strict OEM requirements throughout the service life of a vehicle if they are properly validated. When you understand the required tests and acceptance criteria, you can plan better for validating silicone parts for automotive applications and avoid costly delays in OEM approval.
This guide provides a step-by-step explanation of the basic validation process, as well as information on temperature, fluid exposure and aging validation. Based on actual production in our Dongguan factory, it emphasizes procedures, conditions, acceptance criteria and examples for engines, cooling systems, air intake, exhaust and electrical components.
Why Validation Is Required for Automotive Silicone Parts
Silicone parts need to be validated formally as OEMs require parts to last for 10+ years in the harsh automotive environment and 150,000+km. Even the best designed part could be rejected at sourcing or fail in service. Validation includes temperature, fluid, aging, compression set and mechanical properties.
When used properly and validated for demanding uses, advanced silicones for automotive applications offer the optimum combination of tear resistance and compression set at high temperatures.
How OEM Endorsements and Performance Validation Drive Silicone Adoption
Comprehensive performance validation is the key to successful OEM endorsements. Proven test results are used for engine gaskets, coolant hoses, air intake tubes, exhaust hangers, and electrical connectors. Once validation data shows reliability over extended time, silicone is adopted for additional systems in vehicles.
Test #1 – Temperature Testing (High, Low, and Cycling)
The core of automotive silicone validation is temperature testing. Parts should not crack, harden or become inelastic when subjected to rapid change or exposure to extremes.
High-Temperature Exposure Test Procedure and Acceptance Criteria
High temp exposure mimics proximity to engine, or exhaust. The parts are kept in a controlled oven for 1,000-2,000 hours (or more in certain applications) at 150-200°C. Hardness, appearance and dimensions are checked on a regular basis.
The criteria for acceptance are usually limited hardness change (within ±10 points), no visible cracking or deformation, and compression set less than 25 – 30%. Valve cover gaskets and spark plug boots are frequently tested for this purpose to assure sealing capabilities close to hot engine parts.
Low-Temperature Exposure Test Procedure and Acceptance Criteria
It is important for the cold start performance as well. Samples are placed in a temperature chamber for 24–48 hours at a temperature of –40°C. Flexibility and brittleness are emphasized.
Parts should be flexible and no cracking should occur, and should have only slight increase in hardness. This test is required for any hose that is used in winter or in cold climates, such as coolant hoses, air intake tubes and weatherstripping.
Temperature Cycling Test Procedure and Acceptance Criteria
In a temperature cycle, the vehicle’s operation through the day and night, and throughout the seasons is simulated. Parts cycle between -40°C and 150–200°C for 500–1,000 cycles. After the test, engineers will assess for cracking, seal integrity and changes in mechanical properties.
Sealing force is retained and there is no significant degradation of the successful parts. Engine gaskets and electrical connectors are often subjected to these cycles as an indication of their durability under different operating conditions.
Test #2 – Fluid Exposure Testing (Oils, Fuels, Coolant, Cleaning Agents)
Aggressive fluids are regularly in contact with silicone components. They are proven to be resistant to fluid exposure through testing.
Oil and Fuel Exposure Test Procedure and Acceptance Criteria
Samples are held at high temperatures (approx. 100°C) for 720 to 1,000 hours in engine oil, transmission fluid or fuel. Before and after measurements taken for volume change, hardness, and tensile.
A silicone can have restrictions in this instance and fluorosilicone is sometimes used in fuel or oil contact. Typically, an acceptance tolerance of ±5–10% volume change without cracking is used. Common examples are oil pan seals and transmission seals.
Coolant and Water Exposure Test Procedure and Acceptance Criteria
Coolant immersion tests may be carried out for a minimum of 1,000 to 2,000 hours at 100 °C or above. The sealing force, the hardness and the volume stability (typical ±5%) of the part must be maintained.
It is important for radiator hoses, water pump seals and coolant system items that are exposed to the elements for an extended period of time.
Cleaning Agent and Solvent Exposure Test Procedure and Acceptance Criteria
Most of the under-hood items come into contact with degreasers and solvents during maintenance. Short term exposure tests (24–72 hours) measure surface integrity and property retention. No cracking or hardness change is acceptable. This validation is useful for electrical connectors and exterior shielding.
Test #3 – Aging Test (Thermal, UV, and Ozone Aging)
Aging tests forecast over the life of the vehicle.
Thermal Aging Test Procedure and Acceptance Criteria
Thermal aging is a period of high temperature exposure (1,000–2,000 hours at 150°C). The retained tensile strength, minimal hardness drift and acceptable compression set are the key metrics. Strong thermal aging results are important to engine gaskets and exhaust hangers.
UV Aging Test Procedure and Acceptance Criteria
A weathering chamber (500-1,000 hours) tests for color stability and cracking of the surface. This is important for external weatherstripping and parts that are sometimes in the sun. Acceptance is based on flexibility retention and no degradation visible.
Ozone Aging Test Procedure and Acceptance Criteria
Ozone chamber testing (72-168 hours) is for resistance to cracking under stress. Mechanical characteristics and surface cracks of the under-hood parts and electrical parts should be stable.
Additional Validation Tests for Automotive Silicone Parts
In addition to the basic three, there are a number of supplementary tests that make up the validation package.
Compression Set Test Procedure and Acceptance Criteria
The parts are compressed and then stored at a high temperature (e.g. 150°C) for 24 hours or more. Assessment of recovery is performed, compression set should be < 20-30% for proper long term sealing in valve cover gaskets and coolant hoses.
Tear Resistance and Tensile Strength Test Procedure and Acceptance Criteria
Tensile testers can measure properties before and after exposure to the environment. Typical retention is greater than 80% of the initial value. This makes that engine gaskets and exhaust hangers are resistant to vibrations and mechanical stresses.
Validation Timeline and Documentation for Automotive OEM Approval
Milestones are planning the test, preparing the samples, running the temperature/fluid/aging tests concurrently, analysing the data and reporting. To get iterations fast, coordinate with manufacturer early.
Testing Timeline and Key Milestones for OEM Approval
Comprehensive packages include detailed test reports, material data sheets that include grade and durometer, certifications and traceability records. This documentation is used to ensure the approval of engine gaskets, coolant hoses and spark plug boots.
Required Documentation for Automotive OEM Approval
Comprehensive packages contain detailed test reports, material data sheets specifying grade and durometer, certifications, and traceability records. This documentation supports approval for engine gaskets, coolant hoses, and spark plug boots.
Summary – Temperature, Fluids, and Aging as Core Validation Tests
The key areas of automotive silicone validation are temperature testing (high, low and cycling), exposure to fluids (oils, fuels, coolants, cleaners), and aging (thermal, UV, ozone). The program is completed with compression set, tear resistance and tensile strength supporting tests.
By knowing these needs you can choose and validate materials that will perform well in the real automotive environment. An experienced manufacturer can perform these tests or liaise with a suitable testing facility to speed up the OEM approval and minimise risk.
If you are looking for a new silicone part to use in your car, give us your requirements. We will assist you in designing your own custom validation plan to meet your OEM’s specific requirements.
