Head Gaskets and Sealants

This is a Warning about using Sealants on Modern Head Gaskets.

Most of the head gasket available for aftermarket are either – Composite or Steel (MLS).  Typically composite head gaskets have a steel core, usually perforated, with softer facing materials (graphite or aramid fiber) bonded on each side.  Until recently steel head gaskets consisted of four to six layers of steel bound together, however the trend now is for fewer layers with three or two layers not uncommon and even a single layer now in use on some applications.  Also common to these head gaskets is an impervious silicone coating or viton rubber sealant bonded to the outer layers, a key characteristic in the ability of the gasket to “cold seal”.

Generally speaking, almost all aftermarket head gaskets (both composite and MLS) are designed to be used without additional chemical sealants (i.e. hylomar).  The use of an additional chemical sealant on gaskets not designed for it will actually do more harm than good and affect the gaskets ability to seal.cylinder head gasket

The use of additional chemical sealants such as hylomar can affect the head gaskets ability to:

  • Cold-seal, the ability of the gasket to seal coolant until the engine is first started.
  • Cold Flow, the characteristics of the coating material to creep as the gasket is loaded (clamped), to seal small scratches and imperfections on the head and block surfaces.
  • Reduce the shearing forces that are applied to gasket sealing surfaces by thermal expansion of the cylinder head and block
  • The added thickness of an applied sealant on a head gasket can cause uneven loading and or a loss of torque retension.
  • The use of an additional sealer may also cause relaxation when temperature is introduced
  • Some chemical sealants may also react with the gaskets silicone coating, causing the gasket to deteriorate, and in some cases can cause the deterioration of the chemical sealer itself.

Auto Stop Mechanical Repairs use industry best pectice when replaceing a head gasket. We trust the experts at Southside Cylinder Head Service with all our cylinder head repairs and engine reconditioning. As we can offer a 2 year warranty.

So in summery for DIY Mechanics and other workshops, please read the gasket fitting instructions before fitting your next head gasket. Or consult the supplier about sealants if applicable to that gasket set.

Article content thanks to Southside Cylinder Head Services Brisbane