1Should we change oil every 3000 miles like Dad did?
It depends on conditions, so I have included an article from Consumer
Reports to help you decide.
Our 4-1/2-million-mile test with a fleet of New York City taxicabs turned
some conventional wisdom on its head.
Mobil commercial claims its oil "has been in more Indy 500 winners than any
other oil." Quaker State shows an engine with a terminally corroded inside
what they imply could happen when you use another oil. Exxon's commercial
for its Superflo oil urges motorists to "rely on the tiger."
Oil companies spend millions of advertising dollars each year to convince
you that their oil can make your car's engine perform better and last longer
. And purveyors of motor-oil and engine "treatments" assert that their
products offer engine protection that oil alone can't provide. In our most
ambitious test project ever, we set out to discover whether such claims are
fact or fancy.
One way to gauge the performance of motor oils is to test them on the road.
We did just that, using a fleet of 75 New York City taxicabs. Indeed, the
oil industry itself tests its oils in New York City taxis.
For 22 months, we tested the performance of 20 popular motor oils. Each of
those oils met the industry's latest standards, as certified by a starburst
symbol on the container. (See "It's not just oil," article 3 of 4.) We also
tested Slick 50 Engine Treatment and STP Engine and Oil Treatments.
In addition to the taxicab tests, we had the oils' chemical and physical
properties analyzed by an independent lab. We also surveyed our subscribers
about their oil-changing experiences and preferences, and we sent shoppers
to quick-lube centers across the country to assess the service. Finally,
because changing the oil is just one part of car care, we've reviewed some
other ways you can help keep your car running longer. That report begins on
page 18 (not included in this e-mail).
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, making them ideal for
our purposes. Big-city cabs 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.) For a detailed
description of our test procedures, see "Testing in the Big Apple," article
2 of 4.
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.
The 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
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. However, one of our
laboratory tests measured the viscosity of oils under high-temperature, high
-stress conditions and found essentially no difference between 5W-30 oils
and their 10W-30 brand mates. But at low temperatures, the 5W-30 oil flowed
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.
Of the 20 oils we tested, nine were conventional 10W-30 oils, and eight were
5W-30. We also tested two synthetic oils, Mobil 1 and Pennzoil Performax,
and one synthetic-and conventional blend, Valvoline DuraBlend; all three
were 10W-30 oils.
No brand performed best
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
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, about the thickness of this magazine
page. 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 tested oils provided
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
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 any other.
The bottom line. In our tests, brand didn't matter much as long as the oil
carried the industry's starburst symbol (see "It's not just oil," article 3
of 4). Beware of oils without the starburst; they may lack the full
complement of additives needed to keep modem 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. They 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.
Oil changes: How often?
The long-time mantra of auto mechanics has been to change your oil every
3000 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"
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 the engines 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 protect. To try to get some indication, 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
. Unfortunately, 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,
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-
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 - 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.
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.
None of the tested oils proved better than the others in our tests. There
may be small differences that our tests didn't reveal, but unless you
typically drive under more severe conditions than a New York cab does, you
won't go wrong if you shop strictly by price or availability. Buy the
viscosity grade recommended in your owner's manual, and look for the
starburst emblem. Even the expensive synthetics (typically, $3 or $4 a quart
) worked no better than conventional motor oils in our taxi tests, but they'
re worth considering for extreme driving conditions high ambient
temperatures and high engine load or very cold temperatures.
On the basis of our test results, we think that the commonly recommended 3,
000-mile oil-change interval is conservative. For "normal" service, 7,500-
mile intervals (or the recommendation in your owner's manual) should be fine
. Change the oil at least that often to protect your engine and maintain
your warranty. Even for the severe service experienced by the taxis in our
tests a 6,000- mile interval was adequate. But some severe service -
frequent cold starts and short trips, dusty conditions, trailer towing - may
require a shorter interval. Note, too, that special engines such as diesels
and turbos, which we didn't test, may need more frequent oil changes.
We don't recommend stretching the change interval beyond the automaker's
recommendations, no matter what oil you use. Engine combustion contaminants
could eventually build up and harm engine parts.
As for STP Oil Treatment, STP Engine Treatment, and Slick 50 Engine
Treatment, our advice is simple: If you use an oil with the starburst symbol
, you don't need them.
Testing in the Big Apple
New York City taxicabs played a key role in our massive test project to
evaluate motor oils. For consistency, we used only 1992-93 Chevrolet Caprice
cabs. Each received a precisely rebuilt 4.3-liter V6 at the beginning of
its 60,000-mile test. We started with six rebuilt engines; after each engine
was installed in a cab, the six engines that were removed were rebuilt and
installed in six other cabs-and so on. Using that rotation, we monitored 75
cabs over 4-1/2 million miles of driving in New York City and its environs.
Each oil was tested in three engines.
A local shop completely machined each engine block and crankshaft, rebuilt
the cylinder heads, and installed new bearings, pistons, rings, seals,
gaskets, and oil pump. Though the engines originally had roller lifters and
camshafts, a design that reduces friction, we installed conventional sliding
lifters and camshafts to accelerate wear.
Before the engines were assembled, we measured or weighed the parts most
likely to show wear if the oil wasn't doing its job - the camshafts, valve
lifters, and connecting-rod bearings. Each cab went through a break-in
procedure before hitting the road. During testing, two engine timers
measured the time the engine was running and the time it was in gear.
Over the next 22 months, our engineers paid more than 100 calls - usually
without notice - on the fleet garage. They dropped off test oil and picked
up used-oil samples for ongoing analysis. They also made sure that oil was
being added to the engines when necessary and changed as scheduled.
After each 60,000-mile test, we remeasured the key engine parts. We also
examined combustion-chamber deposits, the color of the valves, scoring of
cylinder walls, and valve-deck deposits for any sign of engine problems.
添加剂什么的没有明显的保护效果。STP Oil Treatment反而增加了既有的粘稠度，这
【在 a******1 的大作中提到】