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tech
More Than You Ever Wanted to
Know About Motor Oil
Edits:
-
v1.0 First there was 1.0. Before that
there was darkness.
-
v1.1 Change in description of
viscosity.
-
v1.2 Updated info on AMSOIL (courtesy
of Morgan McArthur
[email protected])
Choosing the best motor oil
is a topic that comes up frequently in discussions between
motoheads, whether they are talking about motorcycle s 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 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 shearing 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
lose 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.
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 o
f 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 measur ement 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 |
Brand |
VI |
Flash |
Pour |
% Ash |
% Zinc |
20W-50 |
|
|
|
|
|
20W-40 |
|
|
|
|
|
AMSOIL (old) |
136 |
482 |
-38 |
<.5 |
--- |
AMSOIL |
124 |
500 |
-49 |
--- |
--- |
AMSOIL (new) |
157 |
507 |
-44 |
--- |
--- |
Castrol Multi-Grade |
110 |
440 |
-15 |
.85 |
.12 |
Castrol GTX |
122 |
440 |
-15 |
.85 |
.12 |
Quaker State |
121 |
415 |
-15 |
.9 |
--- |
Exxon High Performance |
119 |
419 |
-13 |
.70 |
.11 |
15W-50 |
|
|
|
|
|
Havoline Formula 3 |
125 |
465 |
-30 |
1.0 |
--- |
Chevron |
204 |
415 |
-18 |
.96 |
.11 |
Kendall GT-1 |
129 |
390 |
-25 |
1.0 |
.16 |
Mobil 1 |
170 |
470 |
-55 |
--- |
--- |
Pennzoil GT Perf. |
120 |
460 |
-10 |
.9 |
--- |
Mystic JT8 |
144 |
420 |
-20 |
1.7 |
.15 |
Quaker State Dlx. |
155 |
430 |
-25 |
.9 |
--- |
Red Line |
152 |
503 |
-49 |
--- |
--- |
Red Line |
150 |
503 |
-49 |
--- |
--- |
5W-50 |
|
|
|
|
|
Shell Truck Guard |
130 |
450 |
-15 |
1.0 |
.15 |
Castrol Syntec |
180 |
437 |
-45 |
1.2 |
.10 |
Spectro Golden 4 |
174 |
440 |
-35 |
--- |
.15 |
Quaker State Synquest |
173 |
457 |
-76 |
--- |
--- |
Spectro Golden M.G. |
174 |
440 |
-35 |
--- |
.13 |
Pennzoil Performax |
176 |
--- |
-69
--- |
--- |
Unocal |
121 |
432 |
-11 |
.74 |
.12 |
5W-40 |
|
|
|
|
|
Valvoline All Climate |
125 |
430 |
-10 |
1.0 |
.11 |
Havoline |
170 |
450 |
-40 |
1.4 |
--- |
Valvoline Turbo |
140 |
440 |
-10 |
.99 |
.13 |
10W-30 |
|
|
|
|
|
Valvoline Race |
140 |
425 |
-10 |
1.2 |
.20 |
AMSOIL (old) |
142 |
480 |
-70 |
<.5 |
--- |
Valvoline Synthetic |
146 |
465 |
-40 |
<1.5 |
.12 |
AMSOIL (new) |
162 |
520 |
-76 |
--- |
--- |
15W-40 |
|
|
|
|
|
Castrol GTX |
140 |
415 |
-33 |
.85 |
.12 |
AMSOIL (old) |
135 |
460 |
-38 |
<.5 |
--- |
Chevron Supreme |
150 |
401 |
-26 |
.96 |
.11 |
AMSOIL (new) |
164 |
462 |
-49 |
--- |
--- |
Exxon Superflo Hi Perf |
135 |
392 |
-22 |
.70 |
.11 |
Castrol |
134 |
415 |
-15 |
1.3 |
.14 |
Exxon Superflo Supreme |
133 |
400 |
-31 |
.85 |
.13 |
Chevron Delo 400 |
136 |
421 |
-27 |
1.0 |
--- |
Havoline Formula 3 |
139 |
430 |
-30 |
1.0 |
--- |
Exxon XD3 |
--- |
417 |
-11 |
.9 |
.14 |
Kendall GT-1 |
139 |
390 |
-25 |
1.0 |
.16 |
Exxon XD3 Extra |
135 |
399 |
-11 |
.95 |
.13 |
Mobil 1 |
160 |
450 |
-65 |
--- |
--- |
Kendall GT-1 |
135 |
410 |
-25 |
1.0 |
.16 |
Pennzoil PLZ Turbo |
140 |
410 |
-27 |
1.0 |
--- |
Mystic JT8 |
142 |
440 |
-20 |
1.7 |
.15 |
Quaker State |
156 |
410 |
-30 |
.9 |
--- |
Red Line |
149 |
495 |
-40 |
--- |
--- |
Red Line |
139 |
475 |
-40 |
--- |
--- |
Shell Rotella w/XLA |
146 |
410 |
-25 |
1.0 |
.13 |
Shell Fire and Ice |
155 |
410 |
-35 |
.9 |
.12 |
Valvoline All Fleet |
140 |
--- |
-10 |
1.0 |
.15 |
Shell Super 2000
|
155 |
410 |
-35 |
1.0 |
.13 |
Valvoline Turbo |
140 |
420 |
-10 |
.99 |
.13 |
Shell Truck Guard
|
155 |
405 |
-35 |
1.0 |
.15 |
5W-30 |
|
|
|
|
|
Spectro Golden M.G. |
175 |
405 |
-40 |
--- |
--- |
AMSOIL (old) |
168 |
480 |
-76 |
<.5 |
--- |
Unocal Super |
153 |
428 |
-33 |
.92 |
.12 |
AMSOIL (new)
|
186 |
464 |
-76 |
--- |
--- |
Valvoline All Climate |
130 |
410 |
-26 |
1.0 |
.11 |
Castrol GTX |
156 |
400 |
-35 |
.80 |
.12 |
Valvoline Turbo
|
135 |
410 |
-26 |
.99 |
.13 |
Chevron Supreme
|
202? |
354 |
-46 |
.96 |
.11 |
Valvoline Race< /TD>
|
130 |
410 |
-26 |
1.2 |
.20 |
Chevron Supreme Synt. |
165 |
446 |
-72 |
1.1 |
.12 |
Valvoline Synthetic
|
140 |
450 |
-40 |
<1.5 |
.12 |
Exxon Superflow HP |
148 |
392 |
-22 |
.70 |
.11 |
Havoline Formula 3 |
158 |
420 |
-40 |
1.0 |
--- |
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 |
Valvol ine 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 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 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.
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