Why do some engines use RTV sealer instead of gaskets?
For a period in the 1980s, domestic auto makers thought they could
lower production costs and improve sealing by using RTV (Room
Temperature Vulcanizing) silicone instead of conventional cut
gaskets to seal valve covers, oil pans, timing covers, transmission
pans, and other parts. In theory, the idea made sense. By applying a
thin bead of RTV to such parts, they could be assembled and sealed
in one step.
Engineers liked RTV because it does not take a set like a
conventional cork/rubber cut gasket. Heat causes a cork/rubber
gasket to harden and become brittle with age.
To seal properly, RTV requires both surfaces to be clean, dry and
oil-free. Though installers use RTV all the time with no problems,
car makers apparently could not keep their parts clean enough on the
assembly line to produce a lasting seal with RTV. They found they
were having more oil leaks, not less, with RTV.
Eventually, domestic auto makers dropped RTV in favor of molded
silicone gaskets which combine the installation ease of a
conventional gasket with the sealing properties and durability of
silicone.
When working on an engine that has RTV instead of gaskets, the
installer can either use RTV to reseal the engine, or replace the
RTV with conventional cut gaskets. In some applications, longer
bolts may be necessary to compensate for added gasket thickness.
Some prefer to use RTV because it eliminates the need to stock a lot
of different gaskets. Others prefer to substitute a cut gasket
because of RTV's limitations. Care must be taken when using RTV so
excess sealer does not seep out from between the seating surfaces
and end up someplace where it does not belong.
RTV takes 30 minutes to an hour to set up (full cure takes about 24
hours). The vehicle should not be driven during this time.
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