|
Valve Cover Gasket
Reader Question:
My valve cover gaskets continue to leak oil. I have had them replaced
three times in the last two years, and now they are leaking again. Why
is this happening?
Arnold
Dear Arnold,
Stopping an oil leak can sometimes be
frustrating if you don't find and correct the source of the problem. The
valve cover gaskets are probably just the symptom of the leak and not
the source.
First, you need to determine what kind of
"leak" your car has. There are two types of oil spills, a seep
and a leak. A seep is just that, a slow seepage of oil that does not
produce a drip, is sometimes not noticeable on the pavement as a
"spill," and generally does not seep enough oil to adversely
affect the oil level between oil changes. You may sometimes notice smoke
or a burning odor caused by oil seeping on a hot engine or from coming
into contact with hot exhaust parts. Seeps do not necessarily have to be
repaired immediately.
A leak is just that, a leak that causes a
drip of oil when the vehicle is parked. A leak will produce a puddle of
oil on the pavement, and continues to drip while the vehicle is driven.
A leak can adversely affect oil levels, and if not checked, can drain
enough oil to do internal engine damage. A leak will usually be
accompanied by smoke and a burning odor. Leaks should be corrected
immediately.
It is extremely common to have oil seeps
from a valve cover on just about every car with over 30,000 miles. A
small oil seep at the valve cover gasket will attract dust and dirt that
sticks to the seepage, so this "seep" can be obvious to the
naked eye and still not be serious enough to require replacement of the
gaskets at this time.
Just for grins, I went out and looked at
my car and my wife's car, and both vehicles have valve cover seeps.
Although these seeps are coming from a leaking valve cover gasket, they
do not warrant replacing the gasket at this time. If one of my cars were
taken to a repair shop, I would suspect I would receive a call from the
service manager advising me my valve covers are leaking and should be
replaced. He would be correct to say they are "leaking," but
if I did not experience one of the symptoms of a leaking gasket I
described earlier I would not have the gaskets replaced at this time.
So why do the gaskets leak? The valve
covers are located at the top of the motor and they are a common source
of engine oil seeps and leaks. The valve covers are just that,
protecting covers over the valves and rocker arms at the top of the
engine. The valve covers are bolted to the top of the engine and a large
egg-carton-shaped gasket made of rubber or cork that seals the cover to
the engine. Click
here for illustration.
Oil is pumped from the bottom of the
engine to the top of the engine to lubricate the valve train. This oil
pools inside the valve cover as it slowly drips back inside the engine
via "drain back holes" inside the cylinder head, then it
cycles up to the valve train again. On a V-8 or V-6 engine, the valve
covers are at an angle, and the oil accumulates at the bottom of the
valve cover. The hot exhaust system is located directly below the valve
cover, and a small amount of leaking oil that comes in contact with
these hot exhaust parts can produce smoke and a burning odor. Sludge
build up due to lack of frequent oil changes can cause these drain back
holes to become restricted, slowing the drain back process. This
restriction causes the oil to accumulate in the valve cover longer and
exert more pressure on the valve cover gaskets.
A Positive Crankcase Ventilation (PCV)
valve is inserted in the valve cover itself, and the purpose of this
valve is to act as a vent for excess pressure that accumulates inside
the engine and valve cover areas. Click
here for illustrations A restricted PCV valve can cause this excess
pressure to find new avenues to vent, and an oil gasket or seal is
usually "blown out" to let this pressure escape. Think of the
PCV valve as the valve on top of an old time pressure cooker in your
kitchen. When the pressure inside reaches a certain point, the valve
begins to shake from side-to-side and vent off excess steam. If this
valve is restricted, the steam will find another way to vent off excess
pressure--by blowing the lid off the pot.
If you have a higher-mileage car and are
only experiencing seeps as explained above, then it is my recommendation
to just keep an eye on the gaskets and replace them should the problem
escalate to a true leak. Also, make sure you are following proper
preventive maintenance of your vehicle. The PCV valve should be replaced
periodically, and the PCV system should be inspected to make sure no
restriction is present. I replace the PCV valve when I perform a tune up
on vehicles in my shop. The valve is inexpensive and easy to install.
Changing the engine oil and filter often and inspecting the PCV system
are the best ways to prevent costly engine oil leaks.
Sincerely,
Austin C Davis
Learn more about oil leaks and gaskets
|
