Steve said:
WRONG. The oils have changed. You are right in that respect. BUT engines
are still cast iron and aluminum, and oil still gets dirty in 3,000 miles.
Awful cheap insurance to change it. I never did figger people out who want
to cheap out in this department. Same people who won't check the air in
the tires and then blame the tire manufacturer when they blow I guess.
Few subjects generate as much debate on Usenet as the proper oil change
interval. Since few people bother with oil analysis the debate centers
on time and mileage.
Follow the Money
----------------
Unfortunately, there are market forces that have a vested interest in
convincing vehicle owners to change their oil more often than necessary.
The legal prey of these market forces have become convinced that they
are purchasing "cheap insurance" or "peace of mind" by changing their
oil more often than necessary. Complicating things is the fact that
doing oil changes is one of the few do-it-yourself maintenance tasks
that is still within the ability of the backyard mechanic to perform.
Recreational Oil Changing
-------------------------
The term "recreational oil changer" was coined to define people that
change their oil far more than necessary because they actually enjoy
doing it. It's easy to understand the psychology behind the recreational
oil changing. It's the visceral feel of the tools, the victory when that
old oil filter breaks free, the hot dirty oil pouring out, the joy of
oiling of the gasket on the new filter, that new copper or fiber gasket
on the drain plug, the clean clear oil going in, and the sense of
accomplishment when you start the car, the oil light comes on for a
moment, then goes out. For $8-10 in oil and parts, it's pretty cheap
entertainment, but if people would be content to do it only when it
provides some benefit to the vehicle it would be better.
The 3000 Mile Myth
------------------
The 3000 mile oil change interval has been pounded into people's heads
for decades. It had a scientific basis when engines used
non-multi-weight, non-detergent oil. It no longer has any scientific
basis, but it is still being promoted by certain entities, most notably
the oil change industry in the United States. This myth is also
sometimes known as the "Cheap Insurance Myth."
The 3000 Mile Fact
------------------
There are still vehicles that need 3K oil changes, but it's not because
the oil goes bad after 3K miles. One example is the Saturn S series.
These vehicles have a timing chain system that is very sensitive to
clean oil because oil pressure is used as hydraulic fluid to ratchet up
the timing chain tensioner. If varnish forms in the timing chain
tensioner bore then this system can fail and the chain will become loose
and eventually break. Dealers have gone as far as tearing out the normal
service schedule (6000 miles) and leaving only the severe service
schedule. If your engine is destroyed (under warranty) by a failed
timing chain then the dealer will legitimately request evidence of oil
changes. Unfortunately this problem usually won't manifest itself during
the warranty period.
The Dark Oil Myth
-----------------
Dark oil does not indicate the need for an oil change. The way modern
detergent motor oil works is that minute particles of soot are suspended
in the oil. These minute particles pose no danger to your engine, but
they cause the oil to darken. A non-detergent oil would stay clearer
than a detergent oil because all the soot would be left on the internal
engine parts and would create sludge. If you never changed your oil,
eventually the oil would no longer be able to suspend any more particles
in the oil and sludge would form. Fortunately, by following the
manufacturer's recommended oil change interval, you are changing your
oil long before the oil has become saturated. Remember, a good oil
should get dirty as it does it's work cleaning out the engine. The
dispersant should stop all the gunk from depositing in the oil pan.
The only real way to determine whether oil is truly in need of changing
is to have an oil analysis performed. Since most people don't want to
bother with this, it's acceptable to err heavily on the safe side and
simply follow the manufacturer's recommended change interval for severe
service. There are still a few cars that specify 3K intervals for severe
service, but not many. If you look at countries other than the U.S., the
oil recommended change interval is much higher than even the normal
interval specified by vehicle manufacturers in the U.S.
Severe Service versus Normal Service
------------------------------------
Each manufacturer specifies what constitutes normal and severe service.
Generally, severe service consists of operating the vehicle in a very
muddy or dusty areas (because dust particles get through the air filter
and contaminate the oil more quickly), operating the vehicle in a very
hot areas (heat breaks down oil more quickly), using the vehicle only
for short trips in cold weather (the moisture in the oil never gets
vaporized), or using the vehicle for towing or when carrying a car-top
carrier. You'll often see claims such as "everyone falls into the severe
service category," but these claims are untrue (follow the money and see
who's making these claims). If you primarily do freeway driving in
moderate weather you do not fall into the severe service category. If
you're in doubt, the best way to see if you fall into the severe service
category is to have an oil analysis done at the mileage of the severe
service interval. Many people just like to play it safe and follow the
severe service schedule, which is fine, but there is no benefit in
changing the oil sooner than the severe service schedule states.
As Click and Clack state:
"Over here, we use mostly traditional, petroleum-based motor oil. And
most manufacturers now recommend changing the oil every 7,500 miles. We
recommend doing it every 5,000 miles, because we tend to be more
cautious about protecting the engine. Very few people recommend changing
the oil every 3,000 miles. It's just not necessary, and the
environmental cost is too high."
