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

LOCTITE SI 5900 Oil Resistant Flange Sealant Performance

LOCTITE SI 5900 is engineered for assemblies where a rigid pre-cut gasket may not accommodate flange movement or surface variation. The silicone fills scratches, uneven areas, and gaps up to 6.35 mm, creating a flexible form-in-place gasket on compatible metal, plastic, glass, and ceramic surfaces. Once cured, the seal does not shrink, compress, crack, or relax under normal validated service conditions, helping reduce leakage and recurring maintenance.

The product has a typical tack-free time of approximately 15 minutes and operates across a temperature range of about -55°C to 200°C. Its heavy-bodied consistency also provides useful blow-out resistance, allowing correctly assembled components to undergo low-pressure in-line testing before the sealant has fully cured. This feature can support faster production flow and earlier quality inspection in automotive and industrial assembly operations.

Engine, Gearbox, and Flexible Flange Applications

Typical applications include stamped sheet-metal timing covers, oil sumps, valve covers, transmission housings, gear cases, differential covers, pumps, compressors, and industrial equipment flanges. The sealant is especially suitable where the joint is exposed to engine oil, vibration, thermal cycling, and repeated dimensional movement. Its black appearance provides a professional finish on powertrain and machinery assemblies.

After curing, the silicone provides a Shore A hardness range of approximately 31 to 46, elongation of at least 400%, and tensile strength of at least 1.7 MPa under the referenced laboratory conditions. This balance of flexibility and mechanical strength helps the gasket absorb movement without becoming excessively rigid. The product is also registered under NSF Category P1 in applicable regions for use where food contact is not possible.

7 Benefits of LOCTITE SI 5900 Oil Resistant Flange Sealant

• Excellent oil resistance: Developed for engine, transmission, and industrial lubricant exposure.
• Flexible sealing: Accommodates vibration, joint movement, and thermal expansion.
• Large gap filling: Suitable for validated flange gaps up to 6.35 mm.
• Instant low-pressure seal: Supports early in-line leakage testing.
• Thixotropic application: Reduces sagging and migration after dispensing.
• Broad substrate adhesion: Bonds compatible metals, plastics, glass, and ceramics.
• One-component convenience: Requires no measuring, mixing, or separate curing agent.

How to Apply LOCTITE SI 5900 Oil Resistant Flange Sealant

Remove old gasket material and clean both mating surfaces until they are dry and free from oil, grease, dust, moisture, and loose contamination. Apply a continuous bead to one flange, surrounding bolt holes where required. Assemble the parts within a few minutes because moisture curing begins immediately after exposure to air. Tighten fasteners according to the equipment manufacturer’s recommended sequence and torque.

Allow the assembly to cure adequately before heavy service loading; a seven-day cure is used as an example in the technical data sheet. Cure speed depends on humidity, temperature, bead thickness, and joint geometry. Excess uncured material can be wiped away with a compatible non-polar solvent. Store unopened containers in a dry location between 8°C and 21°C.

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, regional approvals, packaging, and safety information.

Explore our RTV silicone flange sealants for additional flexible gasketing solutions, or browse our automotive gasket sealants for engines, transmissions, pumps, and gear housings. Contact our sales team for quotations, package availability, bulk purchasing, export documentation, and application support.