Head Gaskets and Sealing Compounds

Service Engineering Bulletin - SB043


One of the most common causes of head gasket failures (composite and MLS) is the

application of sealing compounds to the gaskets at the point of cylinder head installation. The

more common of the compounds used include Hylomar® or similar, Kopr Kote® or similar, RTV

silicon sealants (silastic), silver frost spray paint and clear spray enamel. Most, if not all, gasket

manufacturers will not warrant failed head gaskets that have had sealing compounds applied to

them. The exception to this is some copper head gaskets, head gasket saver shims or where it

is specified explicitly by the manufacturer.


Hylomar® is a non-setting and non-hardening jointing compound recommended for cylinder

head shims, inlet manifolds and other similar style gaskets that are not pre-coated by the

manufacturer. Like any sealant, it acts as a lubricant and therefore reduces surface friction. It is

specifically not to be used on single torque head gaskets. Kopr Kote® and similar products are

low-friction anti-seize lubricants manufactured from a combination of micro-size copper flakes

and graphite, dispersed in a water-resistant grease and are fortified with anti-oxidants. They

are a thread anti-seize and have no legitimate application in sealing gaskets. RTV silicone

sealants (silastic) must not be used on head gaskets, other than where some manufactures

require very small amounts of special formulations on the timing gear housing to cylinder block

joint line. Silver frost spray paint and clear spray enamel also have no application on typical

head gaskets.


Victor Reinz gaskets advises that, ‘the use of additional sealing compounds will destroy

composite head gaskets through tearing or breaking of its composite material. In particular, this

is true for the area around the Viton® element because, as the engine warms up and cools

down, the additional compound prevents the element expanding into the spaces provided. The

results are tearing of the material and/or breakage of the Viton® element. MLS cylinder-head

gaskets are designed individually to suit specific engines. Beads, stoppers, elastomer coatings,

and partially vulcanized or moulded-on elements are adapted precisely down to the μm. Sealing

compounds may or may not cure and harden, but they will change the coating thickness which

results in leaks. What’s more, they can flow into oil and coolant channels, where they cause

clogging. Sealing compounds applied in the combustion chamber area will burn out and impair

the bead’s function, resulting in head gasket failure.’


Fel-Pro gaskets advises that, ‘most cylinder head gaskets are coated with Teflon®, Viton® or

silicone-based materials to improve the ‘cold seal’ properties of the engine, so the engine

doesn’t leak fluids before the engine is first started. They caution that chemical sealers can

react adversely with these coating materials, preventing the gasket from cold sealing properly.

This chemical reaction can also cause the gasket to deteriorate and fail. Chemical sealers -

including adhesives, shellac, tacky sealers and RTV silicone - should never be applied to soft

faced, coated head gaskets. However, embossed steel shim and the new multi-layered shim

steel ‘rubber coated embossed’ (RCE) head gaskets, may require a sealer in certain locations

when specified. Fel-Pro also afirms that RTV silicone sealants (silastic) must not be used on

head gaskets.’


In summary, sealing compounds must NEVER be used on head gaskets unless specified by

the manufacturer or warranty will be automatically voided.


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