Henkel LOCTITE SI 5900 Oil Resistant Flange Sealant for Engines and Gearboxes

LOCTITE SI 5900 Oil Resistant Flange Sealant Performance

This moisture-curing silicone creates a flexible gasket that accommodates movement between mating surfaces without relying on a pre-cut gasket. It offers excellent resistance to automotive engine oils and is suitable for joints where vibration, flange movement, and repeated temperature changes may cause conventional rigid gaskets to leak or relax. The heavy-bodied formulation also withstands in-line low-pressure testing before curing begins, helping manufacturers perform earlier leakage inspections and maintain efficient production schedules.

LOCTITE SI 5900 Oil Resistant Flange Sealant is suitable for gaps up to 6.35 mm on compatible metal, plastic, glass, and ceramic substrates. Its typical tack-free time is approximately 15 minutes, while the recommended operating-temperature range is about -55°C to 200°C. Once fully cured, the gasket resists shrinking, cracking, compression, and relaxation under properly validated service conditions.

LOCTITE SI 5900 Oil Resistant Flange Sealant Applications

Typical applications include stamped sheet-metal timing covers, oil sumps, valve covers, transmission housings, differential covers, gear cases, pumps, compressors, and other flexible flange assemblies. It is particularly useful in engines and powertrain systems where the gasket must maintain sealing performance despite exposure to oil, vibration, heat, cooling cycles, and movement between connected parts.

The black finish provides a professional appearance around automotive and industrial components. Its thixotropic behavior reduces migration after dispensing, making the product suitable for manual application, cartridge dispensing, and automated volumetric systems. Actual adhesion and sealing performance depend on substrate condition, flange design, bead dimensions, fastener torque, curing environment, and service-fluid exposure.

7 Commercial Benefits for Automotive and Industrial Users

• Excellent oil resistance: Developed for automotive engines, transmissions, and oil-exposed equipment.
• Flexible cured gasket: Accommodates vibration, joint movement, and thermal expansion.
• Large gap filling: Suitable for validated flange gaps up to 6.35 mm.
• Instant low-pressure sealing: Supports in-line leakage testing before full cure.
• Thixotropic application: Reduces dripping, sagging, and unwanted material migration.
• Broad substrate compatibility: Adheres to many metals, plastics, ceramics, and glass surfaces.
• One-component processing: Requires no weighing, mixing, or separate hardener.

Surface Preparation and Application Guidance

Remove old gasket material and clean both mating surfaces thoroughly. The flange must be dry and free from oil, grease, dust, moisture, oxidation, and loose contamination. Apply a continuous bead to one surface, positioning the sealant around bolt holes where required. Assemble the parts within a few minutes because moisture curing begins immediately after exposure to the atmosphere.

Tighten the fasteners using the equipment manufacturer’s recommended sequence and torque. Allow adequate curing before applying heavy service loads. Henkel provides seven days as an example for full cure, although actual cure speed depends on humidity, temperature, bead thickness, and flange geometry. Excess uncured material can be removed with a compatible non-polar solvent.

Official Resources and Related Gasketing Products

Review the official Henkel LOCTITE SI 5900 product page and the official LOCTITE SI 5900 technical data sheet for current specifications, storage requirements, packaging, and safety information.

Explore our RTV silicone flange sealants for additional flexible form-in-place gasketing products. You can also browse our automotive gasket sealants for engines, transmissions, pumps, timing covers, and gear housings. Store unopened containers in a dry location between 8°C and 21°C. Contact our sales team for quotations, package availability, bulk orders, export documents, and application support.