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Loctite 518 Gel Seal in the 50ml Tube is an anaerobic flange sealant designed for sealing close-fitting joints between rigid metal surfaces and flanges. It is particularly effective on aluminum, which makes it suitable for applications like sealing 2-stroke outboard crankcases.


Key Features:

  • Gel Consistency: The gel form of Loctite 518 prevents it from flowing after application, which is especially useful for vertical or overhead surfaces.
  • Anaerobic Curing: This sealant cures in the absence of air (anaerobic conditions) when confined between close-fitting metal surfaces.
  • High Performance: Provides excellent resistance to high pressure and prevents leakage from gaps or voids in the joint area.
  • Compatibility: It is designed for use on rigid iron, aluminum, and steel flanged mating surfaces.


For a Mercury 2-stroke outboard motor, Loctite 518 is the sealant used by the Mercury Racing factory to seal the crankcase halves. This ensures that the crankcase remains airtight and oil-tight, which is essential for the proper operation of the engine. It helps in preventing the leakage of oil and the ingress of contaminants, maintaining the engine's high performance and longevity.


Application Instructions:

  • Surface Preparation: Ensure that the surfaces to be bonded are clean, dry, and free from grease.
  • Application: Apply a continuous bead of Loctite 518 to one of the flange surfaces. Assemble the parts immediately.
  • Curing: The sealant will start to cure once the parts are assembled and air is excluded. Full cure time depends on the gap and material, but handling strength is typically achieved in a few hours.



  • Improved Sealing: Creates a reliable seal even on slightly contaminated surfaces.
  • Resistance: Provides excellent resistance to oil, water, glycol, and other common fluids.
  • Durability: Maintains seal integrity over a wide temperature range and under dynamic conditions.


Overall, Loctite 518 Gel Seal in the 50ml Tube is a highly effective sealant for crankcase assembly in outboard motors, ensuring reliable engine performance and protection against leaks.


A 50 ml tube of Loctite 518 should be able to seal approximately 5-10 motors, assuming an average usage of 5-10 ml per motor. This estimate can vary based on the actual length and thickness of the bead required for your specific application.

Crankcase Anaerobic Sealant, Loctite 518

SKU: GS1-1-77
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