How Often do I Change
Most vehicle manufacturers recommend changing
the oil once a year or every 7,500 miles in passenger car and
light truck gasoline engines. For diesel engines and turbocharged
gasoline engines, the usual recommendation is every 3,000 miles
or six months.
If you read the fine print, however, you'll discover that
the once a year, 7,500 mile
oil change is for vehicles that are
driven under ideal circumstances. What most of us think of as
"normal" driving is actually "severe service"
driving. This includes frequent short trips (less than 10 miles,
especially during cold weather), stop-and-go city traffic driving,
driving in dusty conditions (gravel roads, etc.), and driving
at sustained highway speeds during hot weather. For this type
of driving, which is actually "severe service: driving, the
recommendation is to change the oil every 3,000 miles or six months.
For maximum protection, most oil companies say to change the
oil every 3,000 miles or three to six months regardless of what
type of driving you do.
A new engine with little or no wear can probably get by on
7,500 mile oil changes. But as an engine accumulates miles, blowby
increases. This dumps more unburned fuel into the crankcase which
dilutes the oil. This causes the oil to break down. So if the
oil isn't changed often enough, you can end up with accelerated
wear and all the engine problems that come with it (loss of performance
and fuel economy, and increased emissions and oil consumption).
Oil Analysis
Truck fleets often monitor the condition of the oil in their
vehicles by having samples analyzed periodically. Oil samples
are sent to a laboratory that then analyzes the oil's viscosity
and acid content. Oil is then burned in a device called a spectrometer
that reveals various impurities in the oil. From all of this,
a detailed report is generated that reveals the true condition
of the oil.
Oil analysis is a great idea for fleets and trucks that hold
a lot of oil. But most consumers would have a hard time justifying
the cost. Having an oil sample analyzed typically costs $12 to
$20 for the lab work and report. Most quick lube shops charge
$16.95 to $19.95 for an
oil change. So why spend your money on
a report that will probably tell you your oil needs changing?
Just change the oil every 3,000 miles and don't worry about it.
Regular oil changes for preventative maintenance are
cheap
insurance against engine wear, and will always save you money
in the long run if you keep a car for more than three or four
years. It's very uncommon to see an engine that has been well
maintained with regular oil changes develop major bearing, ring,
cam or valve problems under 100,000 miles.
What About The Oil Filter?
To reduce the costs of vehicle ownership and maintenance,
many car makers say the
oil filter only needs to be replaced at
every other oil change. Most mechanics will tell you this is
false economy.
The oil filters on most engines today have been downsized
to save weight, cost and space. The "standard" quart-sized
filter that was once common on most engines has been replaced
by a pint-sized (or smaller) filter. You don't have to be a rocket
scientist to figure out that a smaller filter has less total filtering
capacity. Even so, the little filters should be adequate for
a 3,000 mile oil change intervals -- but may run out of capacity
long before a second oil change at 6,000 or 15,000 miles.
Replacing the
oil filter every time the oil is changed, therefore,
is highly recommended.
An engine's main line of defense against abrasion and the
premature wear it causes is the oil filter. The filter's job
is to remove solid contaminants such as dirt, carbon and metal
particles from the oil before they can damage bearing, journal
and cylinder wall surfaces in the engine. The more dirt and other
contaminants the filter can trap and hold, the better.
In today's engines, all the oil that's picked up by the oil
pump is routed through the filter before it goes to the crankshaft
bearings, cam bearings and
valvetrain. This is called "full-flow"
filtration. It's an efficient way of removing contaminants, and
it assures only filtered oil is supplied to the engine. In time,
though, accumulated dirt and debris trapped by the filter begin
to obstruct the flow of oil. The filter should be changed before
it reaches this point, which is why the filter needs to be replaced
when the oil is changed.
If you wait too long to change the filter, there's a danger
that it might become plugged. To prevent this from causing a
catastrophic engine failure due to loss of lubrication, oil filters
have a built-in safety device called a "
bypass valve."
When the pressure drop across the filter exceeds a predetermined
value (which varies depending on the engine application), the
bypass valve opens so oil can continue to flow to the engine.
But this allows unfiltered oil to enter the engine. Any contaminants
that find their way into the crankcase will be pumped through
the engine and accelerate wear.
Filter Replacement
If you do your own oil changes, make sure you get the correct
filter for your engine. Follow the filter manufacturer's listings
in its catalog. Many filters that look the same on the outside
have different internal valving. Many overhead cam engines, for
example, require an "anti-drainback" valve in the filter
to prevent oil from draining out of the filter when the engine
is shut off. This allows
oil pressure to reach
critical engine
parts more quickly when the engine is restarted. Filters that
are mounted sideways on the engine typically require an anti-drainback
valve.
CAUTION: The threads on a spin-on filter must also be the
correct diameter and thread pitch (SAE or metric) for your engine.
If you install a filter with SAE threads on an engine that requires
metric threads (or vice versa), you can damage the threads that
hold the oil filter in place. Mismatched threads can also allow
the filter to work loose, which causes a sudden loss of
oil pressure
that may ruin your engine!
Some people say it's best to change the oil when the oil is
hot (like right after driving), while others say it makes no difference.
CAUTION:
Hot oil is thinner and runs out faster but can
also burn you if you're not careful. In any event, avoid unnecessary
skin contact with oil because oil is a suspected carcinogen (causes
cancer).
Changing the oil when it is cold may take a bit longer because
the oil will drain more slowly from the engine, but there's no
danger of being burned. Also, most of the oil will have drained
down into the oil pan when the engine has sat for a period of
time, which means you'll actually get a little more of the old
oil out of the engine than if you attempt to drain it while it
is still hot.
Used
motor oil should be disposed of properly. The Environmental
Protection Agency does not consider used motor oil to be a hazardous
chemical, but it can foul ground water and does contain traces
of lead. The best way to dispose of used motor oil is to take
it to a service station, quick lube shop, parts store or other
facility for recycling. Your old oil will either be rerefined
into other lubricants or petroleum products, or burned as fuel.
Do not dump used motor oil on the ground, down a drain, into
a storm sewer or place it in the trash. Many landfills will not
accept used motor oil even if it is in a sealed container because
it will eventually leak out into the ground. If you can't find
an environmentally-acceptable way to dispose of the stuff, maybe
you shouldn't be changing your own oil. Service facilities that
do oil changes all have storage tanks and recycling programs to
dispose of used oil.
Keep in mind that these are just tips that you will read either in your car's manual or anywhere on the www, simply google car maintenece. In my experience, the most important thing is to get to know your car. The way that it sounds, the way it performs, how it feels on the road. If you are aware of this, you can usually detect problems that can be attended to before they become expensive issues that can prevent your car from running.
Treat your car right and it will usually return the favor!
