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More than you ever wanted to know about oil
More Than You Ever Wanted to Know About Motor Oil.
by Ed Hackett (edh@maxey.unr.edu)
Choosing the best motor oil is a topic that comes up frequently
in discussions between motoheads, whether they are talking
about motorcycles or cars.
The following article is intended to help you make a choice
based on more than the advertising hype.
Oil companies provide data on their oils most often
referred to as "typical inspection data". This is
an average of the actual physical and a few common
chemical properties of their oils. This information
is available to the public through their
distributors or by writing or calling the company directly. I have
compiled a list of the most popular, premium oils so
that a ready comparison can be made. If your favorite
oil is not on the list get the data from the
distributor and use what I have as a data base.
This article is going to look at six of the most
important properties of a motor oil readily available to the
public: viscosity, viscosity index (VI), flash point,
pour point, % sulfated ash, and % zinc. Viscosity is
the measure of how thick an oil is. This is the most
important property for an engine. An oil with too low
a viscosity can shear and loose film strength at high
temperatures. An oil with too high a viscosity
may not pump to the proper parts at low temperatures
and the film may tear at high rpm.
The weights given on oils are arbitrary numbers
assigned by the S.A.E. (Society of Automotive Engineers).
These numbers correspond to "real" viscosity,
as measured by several accepted techniques.
These measurements are taken at specific temperatures.
Oils that fall into a certain range are designated 5,
10, 20, 30, 40, 50 by the S.A.E. The W means the oil
meets specifications for viscosity at 0 F and is
therefore suitable for Winter use.
The following chart shows the relationship of
"real" viscosity to their S.A.E. assigned numbers.
The relationship of gear oils to engine oils is also shown.
_____________________________________________________________
| |
| SAE Gear Viscosity Number |
| ________________________________________________________ |
| |75W |80W |85W| 90 | 140 | |
| |____|_____|___|______________|________________________| |
| |
| SAE Crank Case Viscosity Number |
| ____________________________ |
| |10| 20 | 30 | 40 | 50 | |
| |__|_____|____|_____|______| |
|_____________________________________________________________|
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42
viscosity cSt @ 100 degrees C
Multi viscosity oils work like this: Polymers are added to a
light base (5W, 10W, 20W), which prevent the oil from
thinning as much as it warms up. At
cold temperatures the polymers are coiled up and
allow the oil to flow as their low numbers indicate.
As the oil warms up the polymers begin to unwind
into long chains that prevent the oil from thinning
as much as it normally would. The result is that
at 100 degrees C the oil has thinned only as much as the
higher viscosity number indicates. Another way of looking
at multi-vis oils is to think of a 20W-50 as a 20
weight oil that will not thin more than a 50
weight would when hot.
Multi viscosity oils are one of the great improvements in oils,
but they should be chosen wisely. Always use a multi grade
with the narrowest span of
viscosity that is appropriate for the temperatures you
are going to encounter. In the winter base your decision
on the lowest temperature you will
encounter, in the summer, the highest temperature you expect.
The polymers can shear and burn forming deposits that can
cause ring sticking and other
problems. 10W-40 and 5W-30 require a lot of polymers
(synthetics excluded) to achieve that range. This has
caused problems in diesel engines, but
fewer polymers are better for all engines. The wide
viscosity range oils, in general, are more prone
to viscosity and thermal breakdown due to the high
polymer content. It is the oil that lubricates,
not the additives. Oils that can do their job
with the fewest additives are the best.
Very few manufactures recommend 10W-40 any more, and some
threaten to void warranties if it is used. It was not
included in this article for that
reason. 20W-50 is the same 30 point spread, but because
it starts with a heavier base it requires less viscosity
index improvers (polymers) to do the job.
AMSOIL can formulate their 10W-30 and 15W-40 with no
viscosity index improvers but uses some in the 10W-40
and 5W-30. Mobil 1 uses no
viscosity improvers in their 5W-30, and I assume the
new 10W-30. Follow your manufacturer's recommendations
as to which weights are appropriate
for your vehicle.
Viscosity Index is an empirical number indicating
the rate of change in viscosity of an oil within a
given temperature range. Higher numbers indicate a low
change, lower numbers indicate a relatively large change.
The higher the number the better. This is one major
property of an oil that keeps your bearings
happy. These numbers can only be compared within a
viscosity range. It is not an indication of how
well the oil resists thermal breakdown.
Flash point is the temperature at which an oil
gives off vapors that can be ignited with a
flame held over the oil. The lower the flash point
the greater tendency for the oil to suffer vaporization
loss at high temperatures and to burn off on hot cylinder
walls and pistons. The flash point can be an indicator of
the quality of the base stock used. The higher the flash
point the better. 400 F is the minimum to prevent possible
high consumption. Flash point is in degrees F.
Pour point is 5 degrees F above the point at which a
chilled oil shows no movement at the surface for 5 seconds
when inclined. This measurement is
especially important for oils used in the winter.
A borderline pumping temperature is given by some manufacturers.
This is the temperature at which the oil will pump and maintain
adequate oil pressure. This was not given by a lot of the
manufacturers, but seems to be about 20 degrees F above the pour
point. The lower the pour point the better. Pour point is in
degrees F.
% sulfated ash is how much solid material is left when
the oil burns. A high ash content will tend to form more
sludge and deposits in the engine. Low ash
content also seems to promote long valve life.
Look for oils with a low ash content.
% zinc is the amount of zinc used as an extreme pressure,
anti-wear additive. The zinc is only used when there is
actual metal to metal contact in the
engine. Hopefully the oil will do its job and this will
rarely occur, but if it does, the zinc compounds react
with the metal to prevent scuffing and wear. A
level of .11% is enough to protect an automobile engine
for the extended oil drain interval, under normal use.
Those of you with high revving, air cooled
motorcycles or turbo charged cars or bikes might want
to look at the oils with the higher zinc content.
More doesn't give you better protection, it gives
you longer protection if the rate of metal to metal
contact is abnormally high. High zinc content can
lead to deposit formation and plug fouling.
The Data:
Listed alphabetically --- indicates the data was not available
Brand VI Flash Pour %ash %zinc
20W-50
AMSOIL 136 482 -38 <.5 ---
Castrol GTX 122 440 -15 .85 .12
Exxon High Performance 119 419 -13 .70 .11
Havoline Formula 3 125 465 -30 1.0 ---
Kendall GT-1 129 390 -25 1.0 .16
Pennzoil GT Perf. 120 460 -10 .9 ---
Quaker State Dlx. 155 430 -25 .9 ---
Red Line 150 503 -49 --- ---
Shell Truck Guard 130 450 -15 1.0 .15
Spectro Golden 4 174 440 -35 --- .15
Spectro Golden M.G. 174 440 -35 --- .13
Unocal 121 432 -11 .74 .12
Valvoline All Climate 125 430 -10 1.0 .11
Valvoline Turbo 140 440 -10 .99 .13
Valvoline Race 140 425 -10 1.2 .20
Valvoline Synthetic 146 465 -40 <1.5 .12
20W-40
Castrol Multi-Grade 110 440 -15 .85 .12
Quaker State 121 415 -15 .9 ---
15W-50
Chevron 204 415 -18 .96 .11
Mobil 1 170 470 -55 --- ---
Mystic JT8 144 420 -20 1.7 .15
Red Line 152 503 -49 --- ---
5W-50
Castrol Syntec 180 437 -45 1.2 .10
Quaker State Synquest 173 457 -76 --- ---
Pennzoil Performax 176 --- -69 --- ---
5W-40
Havoline 170 450 -40 1.4 ---
15W-40
AMSOIL 135 460 -38 <.5 ---
Castrol 134 415 -15 1.3 .14
Chevron Delo 400 136 421 -27 1.0 ---
Exxon XD3 --- 417 -11 .9 .14
Exxon XD3 Extra 135 399 -11 .95 .13
Kendall GT-1 135 410 -25 1.0 .16
Mystic JT8 142 440 -20 1.7 .15
Red Line 149 495 -40 --- ---
Shell Rotella w/XLA 146 410 -25 1.0 .13
Valvoline All Fleet 140 --- -10 1.0 .15
Valvoline Turbo 140 420 -10 .99 .13
10W-30
AMSOIL 142 480 -70 <.5 ---
Castrol GTX 140 415 -33 .85 .12
Chevron Supreme 150 401 -26 .96 .11
Exxon Superflo Hi Perf 135 392 -22 .70 .11
Exxon Superflo Supreme 133 400 -31 .85 .13
Havoline Formula 3 139 430 -30 1.0 ---
Kendall GT-1 139 390 -25 1.0 .16
Mobil 1 160 450 -65 --- ---
Pennzoil PLZ Turbo 140 410 -27 1.0 ---
Quaker State 156 410 -30 .9 ---
Red Line 139 475 -40 --- ---
Shell Fire and Ice 155 410 -35 .9 .12
Shell Super 2000 155 410 -35 1.0 .13
Shell Truck Guard 155 405 -35 1.0 .15
Spectro Golden M.G. 175 405 -40 --- ---
Unocal Super 153 428 -33 .92 .12
Valvoline All Climate 130 410 -26 1.0 .11
Valvoline Turbo 135 410 -26 .99 .13
Valvoline Race 130 410 -26 1.2 .20
Valvoline Synthetic 140 450 -40 <1.5 .12
5W-30
AMSOIL 168 480 -76 <.5 ---
Castrol GTX 156 400 -35 .80 .12
Chevron Supreme 202? 354 -46 .96 .11
Chevron Supreme Synth. 165 446 -72 1.1 .12
Exxon Superflow HP 148 392 -22 .70 .11
Havoline Formula 3 158 420 -40 1.0 ---
Mobil 1 165 445 -65 --- ---
Mystic JT8 161 390 -25 .95 .1
Quaker State 165 405 -35 .9 ---
Red Line 151 455 -49 --- ---
Shell Fire and Ice 167 405 -35 .9 .12
Unocal 151 414 -33 .81 .12
Valvoline All Climate 135 405 -40 1.0 .11
Valvoline Turbo 158 405 -40 .99 .13
Valvoline Synthetic 160 435 -40 <1.5 .12
All of the oils above meet current SG/CD ratings and all
vehicle manufacturer's warranty requirements in the
proper viscosity. All are "good enough", but
those with the better numbers are icing on the cake.
The synthetics offer the only truly significant
differences, due to their superior high temperature
oxidation resistance, high film strength,
very low tendency to form deposits, stable viscosity base,
and low temperature flow characteristics. Synthetics are
superior lubricants compared to traditional petroleum oils.
You will have to decide if their high cost is
justified in your application.
The extended oil drain intervals given by the
vehicle manufacturers (typically 7500 miles)
and synthetic oil companies (up to 25,000 miles)
are for what is
called normal service. Normal service is defined
as the engine at normal operating temperature,
at highway speeds, and in a dust free environment. Stop
and go, city driving, trips of less than 10 miles,
or extreme heat or cold puts the oil change
interval into the severe service category,
which is 3000 miles for most vehicles.
Synthetics can be run two to three times the mileage
of petroleum oils with no problems. They do not react
to combustion and combustion by-products to the extent
that the dead dinosaur juice does. The longer drain
intervals possible help take the bite out of the higher
cost of the synthetics. If your car or bike is still
under warranty you will have to stick to the
recommended drain intervals. These are set for
petroleum oils and the manufacturers make no
official allowance for the use of synthetics.
Oil additives should not be used. The oil companies
have gone to great lengths to develop an additive
package that meets the vehicle's requirements.
Some of these additives are synergistic, that is
the effect of two additives together is greater
than the effect of each acting separately.
If you add anything to the oil you may upset
this balance and prevent the oil from performing to specification.
The numbers above are not, by any means,
all there is to determining what makes a
top quality oil. The exact base stock used,
the type, quality, and
quantity of additives used are very important.
The given data combined with the manufacturer's
claims, your personal experience, and the
reputation of the oil among others who use it
should help you make an informed choice.
I just recieved this data from our local oil distributor. It is
the update on the new Mobil 1 formulation and that for the new
Castrol Syntec. They did not have the numbers for the new
Valvoline synthetics yet. The data on the new Mobil 1 is pretty
impressive. Based on these numbers, price, and availiability,
there is little need to look further for a synthetic oil.
The Syntec seems to be compromised by it's wide viscosity range.
Notice that the pour point is for all practical purposes, no
better than the Mobil 1 15W-50. (actually, it's not as good)
While, meeting the viscosity parmeters, the wide range is
probably for marketing purposes. The Mobil 1 15W-50 will pump at
-35 degrees F, which is as good as some conventinal 5W-30 oils.
Any of the ester based synthetics (AMSOIL, Mobil 1, and Syntec),
will give you the benefits that Castrol is making a big deal of
in their advertising. The ability to cling to metal walls is due to
the polar nature of the ester base stock, not something unique to
Castrol's formulation.
The Data: (add to your current article)
Brand and Weight VI Flash Pour %ash %zinc
Syntec 5W-50 180 437 -49 1.2 0.10
Mobil 1 5W-30 165 445 -65 --- ---
10W-30 160 450 -65 --- ---
15W-50 170 470 -55 --- ---
Ed Hackett edh@wheeler.wrc.unr.edu
The Desert Research Institute
DoD #0200 WMTC BMWRA DIOC Reno, Nevada (702)673-7380
KotLS KtoLE DotD #0003
I'm not really a chemist,
I'm just one of them motorsickle
sonsabitches.
900SS K100RS 501 CAMEL __=o&o>__