The
first symptoms of a head gasket that is failing are usually a slow loss
of coolant with no visible leaks, engine overheating and/or a Check
Engine light with cylinder misfire codes.
The first symptoms of
a head gasket that is failing are usually a slow loss of coolant with
no visible leaks, engine overheating and/or a Check Engine light with
cylinder misfire codes.
The Onboard Diagnostic II system should
detect any misfires that occur due to a loss of compression or spark
plugs fouled by coolant seeping into a combustion chamber. So if a
vehicle has a Check Engine light on and a cylinder misfire code, the
spark plug in that cylinder should be removed and inspected for coolant
fouling. A compression or leak-down test should also be done to see if
the cylinder is losing compression. Internal coolant leaks caused by a
leaky head gasket can usually be diagnosed by pressure-testing the
cooling system.
Regardless of the cause, a head gasket failure is bad news for the vehicle owner.
Depending
on the application and how much labor it requires, the repair bill
might run $1,500 or more for parts and labor. The parts required to
replace a head gasket include not only the head gasket itself, but also
all the other gaskets that have to be replaced to disassemble the top
of the engine.
This includes the intake and exhaust manifold
gaskets, too, plus new cylinder head bolts if the application is a late
model engine with non-reusable torque-to-yield (TTY) head bolts. It may
be tempting to save a few bucks on off-brand gaskets.
While these
off-brand gaskets might look similar to branded products, they often do
not feature the material characteristics and design enhancements
required for trouble-free sealing.
Depending on the mileage on the
engine, additional parts should also be replaced at the same time. This
might include the timing belt if the engine has an overhead cam
(recommended replacement intervals for the belt range from 60,000 to
100,000 miles on most vehicles), the water pump, spark plugs and
filters. The coolant should also be changed if it is more than five
years old, or has more than 150,000 miles on it (long-life coolants),
or if it is more than three years old (older green formula coolant). If
the head gasket caused an internal coolant leak, it’s possible the
oxygen sensor(s) may have also been fouled by silicates in the
antifreeze (if the cooling system was filled with older green formula
coolant, or a hybrid HOAT or G-05 formula coolant).
What are the risks of reusing torque-to-yield (TTY) head bolts on late-model engines?
The
risks are bolt breakage and uneven gasket loading or loss of torque
that can cause a newly installed head gasket to leak. TTY head bolts
are designed for one-time use because they stretch permanently once
they are torqued down. This helps even out the clamping force of the
cylinder head on the head gasket.
But if the bolts are reused,
stretching them even further greatly increases the risk of the bolt
breaking. Some replacement head gaskets come with new TTY head bolts,
but others do not. If the bolts are not included, they should be
included as an add-on sale. Many customers may not realize they should
not reuse TTY head bolts. If an engine has conventional head bolts,
it’s okay to reuse them — provided the bolts are in good condition and
the bolts are not stretched.
Bolts can be cleaned, then lightly
oiled and reused. Dirty or damaged threads, or failing to lubricate the
bolts before they are installed can cause false torque readings when
the bolts are tightened, which may allow the head gasket to leak.