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By: Ed Hackett
Choosing the best motor oil is a topic that comes up frequently in
discussions between motorheads, whether they are talking about motorcycles or
ATV's. 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 availiable to the public: viscosity, viscosity index (VI), flash
point, pour point, % sulfated ash, and % zinc.
Viscosity
Viscosity is a measure of the "flowability" of an oil. More
specifically, it is the property of an oil to develop and maintain a certain
amount of sheering stress dependent on flow and then to offer continued
resistance to flow. Thicker oils generally have a higher viscosity, and thinner
oils a lower viscosity. 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 various low temperatures depending on weight, and is therefore
suitable for Winter use. 5W is tested at -25C, 10W at -20C, 15W at -15C, and 20W
at -10C.
Multi-viscosity
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.
Choosing your oil!
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 manufacturers 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. Other multigrade synthetics may not use VI
improvers either. The full literature available from the oil company should
include this information. Follow your manufacturer's recommendations as to which
weights are appropriate for your vehicle.
Viscosity Index
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
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 tendancy 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 (Fahrenheit)
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
% sulfated ash is how much solid material is left when the oil is
reacted with sulfuric acid and burned. This is used to quantify the amount of
metallic antiwear and detergent additives in the oil. Zinc dithiophosphate is a
common detergent and antiwear additive that is reflected in this test.
Zinc
% 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 reving, air cooled
motorcycles or ATV's 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.
The Data: (Note: this data is mostly from 1991 and is for SG rated oils. Some of
the data is current, and I am working on collecting the most recent data. I have
found over the years that the "better" oils remain the "better"
oils. It is still valid as a place to start in your own search. The formulation
of oils is constantly being updated and subject to change by the manufacturer at
any time. The best thing to do is collect data on the oils you are interested in
directly from the oil company.)
All Oils are 20W-50W
| Brand |
Visc. Index |
Flash |
Pour |
% of Ash |
% of Zinc |
| Amsoil |
151 |
507 |
-45 |
N/A |
N/A |
| Amsoil Series 2000 |
155 |
474 |
-47 |
N/A |
N/A |
| Castrol GTXHavoline Formula |
122 |
440 |
-15 |
.85 |
.12 |
| Chevron Supreme |
140 |
428 |
-17 |
1.0 |
N/A |
| Exxon High Performance |
119 |
419 |
-13 |
.70 |
.11 |
| Havoline Formula 3 |
125 |
465 |
-30 |
1.0 |
N/A |
| Kendall GT-1 |
129 |
390 |
-25 |
1.0 |
.16 |
| Pennzoil GT |
120 |
460 |
-10 |
.9 |
N/A |
| Quaker State Perf. |
121 |
440 |
-20 |
N/A |
N/A |
| Valvoline Synthetic |
146 |
465 |
-40 |
1.5 |
.12 |
All Oils are 15W-40W
| Brand |
Viscosity Index |
Flash |
Pour/deg.(F) |
% of Ash |
% of Zinc |
| Amsoil |
165 |
462 |
-49 |
N/A |
N/A |
| Castrol GTX |
134 |
415 |
-15 |
1.3 |
.14 |
| Exxon XD3 Extra |
135 |
399 |
-11 |
.95 |
.13 |
| Kendall GT-1 |
135 |
410 |
-25 |
1.0 |
.16 |
| Quak. State HDX Plus |
148 |
420 |
-25 |
1.37 |
N/A |
| Valvoline Turbo |
140 |
420 |
-10 |
.99 |
.13 |
All Oils are 10W-30W
| Brand |
Visc. Index |
Flash |
Pour/deg.(F) |
% of Ash |
% of Zinc |
| Amsoil |
154 |
520 |
-60 |
N/A |
N/A |
| Castrol GTX |
140 |
415 |
-33 |
.85 |
.12 |
| Chevron Supreme |
150 |
419 |
-27 |
.9 |
N/A |
| Exxon Superflo Supreme |
133 |
400 |
-31 |
.85 |
.13 |
| Havoline Formula 3 |
139 |
430 |
-30 |
1.0 |
N/A |
| Mobil 1 |
160 |
450 |
-65 |
N/A |
N/A |
| Quaker State |
140 |
410 |
-30 |
.9 |
N/A |
| Valvoline Synthetic |
140 |
450 |
-40 |
1.4 |
.12 |
All of the oils above meet current SG/CD ratings and all vehicle manufacture'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
tendancy 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 justifed in your
application.
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 ATV 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. Some oil companies, AMSOIL being
an example, offer their own engine warranties. If the oils are used in
compliance with the company's recommendations (including extended drain
intervals) and a problem is caused by the engine oil, the company will pay for
the repairs. Check with the company for specifics of any warranties offered.
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.
Ed Hackett [email protected]
The Desert Research Institute
Reno, Nevada (702) 673-7380
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