Just in case the original source urls go away, I'm posting the text here:
Here is the complete text of the Consumer reports oil test that should dispel
any myths regarding synthetics etc...
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From Consumer Reports:
Performance
Testing the Oils
We put identical rebuilt engines with precisely measured parts into the
cabs at the beginning of the test, and we changed their oil every 6,000
miles. That's about twice as long as the automakers recommend for the
severe service that taxicabs see, but we chose that interval to
accelerate the test results and provide worst-case conditions. After
60,000 miles, we disassembled each engine and checked for wear and
harmful deposits. Our test conditions were grueling, to say the least.
The typical Big Apple cab is driven day and night, in traffic that is
legendary for its perversity, by cabbies who are just as legendary for
their driving abandon.
When the cabs aren't on the go, they're typically standing at curbside
with the engine idling, far tougher on motor oil than highway driving.
What's more, the cabs accumulate lots of miles very quickly. They don't
see many cold start-ups or long periods of high-speed driving in extreme
heat. But our test results relate to the most common type of severe
service, stop-and-go city driving.
Each of the 20 oils we studied was tested in three cabs to provide
meaningful test results even if a few cabs fell out with mechanical
problems or because of accidents. (Six of the 75 engines did, in fact,
have problems, none apparently related to the oil's performance.) Our
shoppers all across the country bought hundreds of quart containers of
oil. Some brands had slightly different formulations in different areas,
but all the oils included a full package of additives.
An independent lab helped us identify the most representative
formulations of each brand. Our engineers transferred containers of that
oil to coded 55-gallon drums and hauled them to the fleet garage for
testing. Ideally, oil should be thin enough to flow easily when the
engine is cold and remain thick enough to protect the engine when it's
hot. The lab analyses of each oil's viscosity characteristics (its
ability to flow) indicate that motor oils have improved since 1987, when
we last tested them.
This time, far fewer test samples failed to meet the viscosity standards
for their grade, and those were typically outside the limits by only a
slight amount. No brand stood out as having a significant problem. We
tested oils of the two most commonly recommended viscosity grades,
10W-30 and 5W-30. Automakers specify grades according to the temperature
range expected over the oil-change period. The lower the number, the
thinner the oil and the more easily it flows.
In 5W-30 oil, for example, the two numbers mean it's a "multiviscosity"
or "multigrade" oil that's effective over a range of temperatures. The
first number, 5, is an index that refers to how the oil flows at low
temperatures. The second number, 30, refers to how it flows at high
temperatures. The W designation means the oil can be used in winter.
A popular belief is that 5W-30 oils, despite their designation, are too
thin to protect vital engine parts when they get hot. But one of our lab
tests found otherwise. In that test, the viscosity of oils was measured
under high-temperature, high-stress conditions. Essentially, no
difference was found between 5W-30 oils and their 10W-30 brand mates.
But at low temperatures, the 5W-30 oil flowed more easily. Viscosity
grade is important, so be careful. Recommendations vary with the make,
engine and model year of the car, so check your owner's manual and ask
the mechanic for the proper grade of oil.
Results
If you've been loyal to one brand, you may be surprised to learn that
every oil we tested was good at doing what motor oil is supposed to do.
More extensive tests, under other driving conditions, might have
revealed minor differences. But thorough statistical analysis of our
data showed no brand, not even the expensive synthetics, to be
meaningfully better or worse in our tests. After each engine ran about
60,000 miles (and through 10 months of seasonal changes), we
disassembled it and measured the wear on the camshaft, valve lifters and
connecting-rod bearings.
We used a tool precise to within 0.00001 inch to measure wear on the key
surfaces of the camshaft, and a tool precise to within 0.0001 inch on
the valve lifters. The combined wear for both parts averaged only 0.0026
inch. Generally, we noted as much variation between engines using the
same oil as between those using different oils. Even the engines with
the most wear didn't reach a level where we could detect operational
problems.
We measured wear on connecting-rod bearings by weighing them to the
nearest 0.0001 gram. Wear on the key surface of each bearing averaged
0.240 gram, about the weight of seven staples. Again, all the oils
provided adequate protection. Our engineers also used industry methods
to evaluate sludge and varnish deposits in the engine. Sludge is a mucky
sediment that can prevent oil from circulating freely and make the
engine run hotter. Varnish is a hard deposit that would remain on engine
parts if you wiped off the sludge. It can make moving parts stick.
All the oils proved excellent at preventing sludge. At least part of the
reason may be that sludge is more apt to form during cold startups and
short trips, and the cabs were rarely out of service long enough for
their engine to get cold. Even so, the accumulations in our engines were
so light that we wouldn't expect sludge to be a problem with any of
these oils under most conditions. Variations in the buildup of varnish
may have been due to differences in operating temperature and not to the
oils. Some varnish deposits were heavy enough to lead to problems
eventually, but no brand consistently produced more varnish than others.
The bottom line: Our tests indicate that brand doesn't matter much, as
long as the oil carries the industry's starburst symbol. Beware of oils
without the starburst, as they may lack the full complement of additives
needed to keep modern engines running reliably.
One distinction: According to the laboratory tests, Mobil 1 and Pennzoil
Performax synthetics flow exceptionally easily at low temperatures, a
condition our taxi tests didn't simulate effectively. Mobil 1 and
Pennzoil Performax synthetics also had the highest viscosity under
high-temperature, high-stress conditions, when a thick oil protects the
engine. Thus, these oils may be a good choice for hard driving in
extreme temperatures.
Note, too, that a few automakers recommend specific brands of motor oil
in the owner's manual. You may need to follow those recommendations to
keep a new car in warranty.
Testing Slick 50 and STP
We also tested Slick 50 and STP Engine Treatments and STP Oil Treatment,
each in three cabs. (Slick 50 costs $17.79 per container. STP Engine
Treatment has been discontinued.) All three boast that they reduce
engine friction and wear. The engine treatments are added with the oil
(we used Pennzoil 10W-30). They claim they bond to engine parts and
provide protection for 25,000 miles or more. We used each according to
instructions.
The STP Oil Treatment is supposed to be added with each oil change. It
comes in one formulation (black bottle, $4.32) for cars with up to
36,000 miles, another (blue bottle, $3.17) for cars that have more than
36,000 miles or are more than four years old. We used the first version
for the first 36,000 miles, the second for the rest of the test, again
with Pennzoil 10W-30. When we disassembled the engines and checked for
wear and deposits, we found no discernible benefits from any of these
products. The bottom line: We see little reason why anyone using one of
today's high-quality motor oils would need these engine/oil treatments.
One notable effect of STP Oil Treatment was an increase in oil
viscosity. It made our 10W-30 oil act more like a 15W-40, a grade not
often recommended. In very cold weather, that might pose a risk of
engine damage.
Oil Changes
How Often?
The long-time mantra of auto mechanics has been to change your oil every
3,000 miles. Most automakers recommend an oil change every 7,500 miles
(and a specific time interval) for "normal" driving, and every 3,000
miles for "severe" driving (frequent trips of less than four or five
miles, stop-and-go traffic, extended idling, towing a trailer, or dusty
or extremely cold conditions). Many motorists' driving falls into one or
more of those "severe" categories.
In our survey, almost two-thirds of our readers said they had their oil
changed every 3,000 miles or less. They may be following the thinking
expressed by one of our staffers: "I have my oil changed every 3,000
miles because that's what my father did, and all his cars lasted for
many years." To determine whether frequent oil changes really help, we
changed the oil in three cabs every 3,000 miles, using Pennzoil 10W-30.
After 60,000 miles, we compared those engines with those from our base
tests of the same oil, changed every 6,000 miles. We saw no meaningful
differences.
When Mobil 1 synthetic oil came out, Mobil presented it as an oil that,
while expensive, could go 25,000 miles between changes. That claim is no
longer being made. But Mobil 1 is still on the market, selling at a
premium (along with pricey synthetic competitors from several other
companies). And synthetic oil's residual reputation as a long-lasting
product may still prompt some people to stretch their oil changes longer
than the automaker recommends.
Determining whether synthetic oils last longer than conventional ones
would require a separate test project. To try to get some indication as
to whether synthetic oils last longer, we put Mobil 1 synthetic into
three cabs and changed their oil every 12,000 miles. We intended to
compare the results of these tests with those from the three taxicabs
whose Mobil 1 was changed at our normal interval, every 6,000 miles. Two
of the three engines using the 12,000-mile interval developed problems.
(We couldn't attribute those problems to the oil.) The third engine
fared no worse than the three whose oil had been changed at 6,000-mile
intervals.
The bottom line: Modern motor oils needn't be changed as often as oils
did years ago. More frequent oil changes won't hurt your car, but you
could be spending money unnecessarily and adding to the nation's energy
and oil-disposal problems. Even in the severe driving conditions that a
New York City taxi endures, we noted no benefit from changing the oil
every 3,000 miles rather than every 6,000. If your driving falls into
the "normal" service category, changing the oil every 7,500 miles (or at
the automaker's suggested intervals) should certainly provide adequate
protection. (We recommend changing the oil filter with each oil change.)
We don't recommend leaving any oil, synthetic or regular, in an engine
for 12,000 miles, because accumulating contaminants, such as solids,
acids, fuel and water, could eventually harm the engine. What's more,
stretching the oil-change interval may void the warranty on most new
cars.
Where Should You Go?
Choosing the right motor oil is only the first step. Someone has to
change the oil regularly. Should you economize by doing the work
yourself? Should you go to the local service station? The car dealer? A
quick-lube center? Our own tests plus the experiences of some 900 of our
readers provide some answers to those questions. We asked readers how
often they change their car's oil, who does it and how satisfied they
are with the service. And we sent shoppers in several parts of the U.S.
to 55 local quick-lube centers to assess the service and to collect oil
samples.
The car owners we surveyed used these four options in roughly equal
measure:
Service station or garage. Many local garages compete with quick-lube
centers by charging $20 to $30 or so for an oil change. And the service
station may be a good place to go for other repairs and maintenance.
New-car dealer. Some dealers offer regular oil changes for little or no
extra cost with the purchase of a car. General Motors dealers offer a
"one price" oil change that's competitive with the prices charged by
quick-lube centers. But absent such a one-price arrangement, expect such
dealer-performed oil changes to cost about $30. Car dealers were also
the slowest and least convenient, according to our survey.Do it
yourself. People change their own oil not only to save money (oil and
filter together can cost as little as $10), but also for the
satisfaction of knowing the job was done right. If you handle your own
oil changes, be sure to dispose of the used oil properly to prevent it
from polluting the environment. It's best to take the oil to a local
service station that accepts used oil, or to a municipal household
hazardous-waste collection center. Whatever you do, don't pour the oil
down the sewer or discard it with the rest of the household trash.
Quick-lube centers. These operations promise to get you in and out in as
little as 10 minutes. Of our surveyed readers, 90% reported that they
waited less than half an hour. Cost: $15 to $33. Although about 77% of
readers were highly satisfied with quick-lube centers, service stations
and car dealers earned even higher scores.
How Reliable Are Quick-Lubes?
Quick-lube centers promise a lot for a little. They say they'll change
the oil and filter, top off other fluids, check the tire pressure,
perhaps even vacuum the car's interior, all in about half an hour and
for about $25. To find out how well the centers deliver on that promise,
we asked Consumer Reports shoppers in California, Florida, Illinois and
Texas to take cars in for an oil change at quick-lube centers last
winter. The shoppers visited outlets run by Jiffy Lube, Kmart, Wal-Mart
and others. We didn't visit enough centers often enough to rank them
from best to worst. But we did see patterns in the service.
The shops we visited didn't cut corners. The oil they dispense from a
drum is comparable with the oil you can buy in one-quart containers. The
shops also did a good job of filling oil and other fluids to the proper
levels. But the shops do make mistakes. The most common, one that any
servicer can make: using the wrong viscosity grade of oil for the car.
Many oil-change centers maintain computerized data on which oil grades
are recommended for specific makes and models. But in the cases where we
could compare the oil grade we got with the grade the car's owner's
manual listed as preferred, the quick-lube shop used a different grade
half the time. You might not be able to tell if your car got, say,
10W-40 instead of 5W-30. And one oil change with the wrong grade in
normal weather shouldn't harm the engine. But the engine may not always
be adequately protected if it has the wrong grade of oil in very hot or
very cold weather.
The shops are usually fast and economical. They took from 10 minutes to
more than an hour to service our shoppers' cars. Average time: 35
minutes. The cost ranged from $15 to $33, with the average at $23.
Service varies. Some centers change the oil and filter, period. Others
include a variety of services. But note that 18% of our readers who used
a quick-lube center complained that it tried to sell them services they
didn't want. And a few readers (8%) said the centers didn't perform a
necessary service, changing the oil filter.
Consumer Reports Recommendations
Change the oil yourself only if you have the tools and equipment, can
safely dispose of the used oil, and feel that it's worth the hassle to
save about $15. Otherwise, any of the commercial alternatives can do an
adequate job. Use a garage or the dealer when you also need other work
done at the same time. Choose among quick-lube centers according to
price and service, and be sure you tell the center what grade of oil
your car needs. Discount coupons are common, so you need never pay full
price.
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