Question:My mechanic says my engine has a blown head
gasket. Is this serious?
Answer: It is because (1) it will be expensive to replace,
(2) it is probably the result of some other underlying problem,
and (3) additional repairs may be required in addition to replacing
the head gasket itself.
The head gasket seals the cylinder head to the block. When
it blows, it may allow coolant to leak into the engine's cylinders
and/or allow compression to be lost between adjacent cylinders
or to the outside.
WHY HEAD GASKETS FAIL
Head gaskets typically fail at the weakest point, which is
the thinnest area between adjacent cylinders. The gasket cracks
or burns through, allowing compression to leak between the cylinders.
This causes a drastic drop in power that is hard to ignore.
The engine may still run, but very poorly.
If the gasket leaks coolant, it may cause the engine to overheat.
Coolant in the crankcase or cylinder is also not a good thing
to have because it dilutes the oil and accelerates wear. If enough
coolant leaks into a cylinder, it may even "hydrolock"
the engine preventing it from turning over when you attempt to
start it.
Conditions such as engine overheating and abnormal combustion
(detonation and/or preignition) can also cause a head gasket to
fail.
Improper installation may be another factor. If the person
who installed the gasket did not torque the head bolts in the
proper sequence or to the specified value, it can cause the gasket
to leak and fail. Also, if the head and block were not clean,
flat and finished properly (too rough a surface finish) when the
gasket was originally installed, it could contribute to a leakage
problem.
Some engines also have a reputation for eating head gaskets.
The design of the head along with the location, size and load
on the head bolts has a lot to do with how long the head gasket
will keep its seal. In some of these engines, the problem is
the design of the engine while in others it is the design of the
head gasket.
GASKET REPLACEMENT
To replace a blown head gasket, the cylinder head must be
removed from the engine. This can be a major undertaking depending
on the type of engine and how much other stuff has to be removed
to pull the head.
Once the head is off, the mating surfaces of both the head
and block should be inspected for flatness as well as any damage
that might have contributed to the gasket's failure or might prevent
a new gasket from sealing properly. If the head is warped, it
will not seal the new gasket properly and sooner or later it will
again fail. Resurfacing and/or straightening the head may be
necessary. An inspection of the head may also reveal cracks or
other damage that will have to be repaired before it can go back
on your engine.
You should know that several gasket manufacturers offer special
"problem solving" head gaskets for certain engines that
have a high incidence of head gasket failure. These gaskets are
often made of high heat materials such as graphite and have other
special features such as additional combustion chamber armor,
added sealing beads, more thickness, etc.
