More Than You
Ever Wanted to Know About Motor Oil
Author: Ed Hackett
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 advertizing hype.
Oil companies provide data on their oils most often refered 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 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
theproper 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.
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 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 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 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 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 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 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 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.
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.)
[An * after the oil name indicates current SH rated version.]
Listed alphabetically --- indicates the data was not avaliable
20W-50
| Brand |
VI |
Flash |
Pour |
%ash |
%zinc |
| AMSOIL* |
151 |
507 |
-45 |
--- |
--- |
| AMSOIL Series 2000 |
155 |
474 |
-47 |
--- |
--- |
| Castrol GTX |
122 |
440 |
-15 |
.85 |
.12 |
| Chevron Supreme* |
140 |
428 |
-17 |
<1 |
--- |
| 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 Perf.* |
121 |
440 |
-20 |
--- |
--- |
| Quaker State Motorcycle |
140 |
440 |
-25 |
--- |
--- |
| Red Line |
150 |
503 |
-49 |
--- |
--- |
| Shell Fire and Ice* |
126 |
450 |
-10 |
.9 |
.12 |
| Shell Truck Guard* |
130 |
450 |
-15 |
1.0 |
.12 |
| Spectro Golden 4 |
174 |
440 |
-35 |
--- |
.15 |
| Spectro Golden M.G. |
174 |
440 |
-35 |
--- |
.13 |
| Ultra Chem |
190 |
455 |
-34 |
--- |
--- |
| 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 DuraBlend |
126 |
455 |
-17 |
<1.5 |
.125 |
| Valvoline Synthetic |
146 |
465 |
-40 |
<1.5 |
.12 |
15W-50
| 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 |
| Chevron Supreme* |
175 |
460 |
-38 |
1.45 |
--- |
| Quaker State Synquest* |
175 |
460 |
-50 |
--- |
--- |
| Pennzoil Performax |
176 |
--- |
-69 |
--- |
--- |
5W-40
| Havoline |
170 |
450 |
-40 |
1.4 |
--- |
15W-40
| AMSOIL* |
165 |
462 |
-49 |
--- |
--- |
| Castrol |
134 |
415 |
-15 |
1.3 |
.14 |
| Chevron Delo 400* |
134 |
424 |
-38 |
<1 |
--- |
| 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 |
| Quaker State* |
129 |
420 |
-25 |
--- |
--- |
| Quaker State HDX* |
146 |
440 |
-30 |
.97 |
--- |
| Quaker State HDX Plus* |
148 |
420 |
-25 |
1.37 |
--- |
| Red Line |
149 |
495 |
-40 |
--- |
--- |
| Shell Rotella w/XLA* |
146 |
414 |
-32 |
1.0 |
.12 |
| Valvoline All Fleet |
140 |
--- |
-10 |
1.0 |
.15 |
| Valvoline DuraBlend |
137 |
450 |
-17 |
<1.5 |
.125 |
| Valvoline Turbo |
140 |
420 |
-10 |
.99 |
.13 |
10W-30
| AMSOIL* |
154 |
520 |
-60 |
--- |
--- |
| Castrol GTX |
140 |
415 |
-33 |
.85 |
.12 |
| Chevron Supreme* |
150 |
419 |
-27 |
<1 |
--- |
| 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* |
140 |
410 |
-30 |
.9 |
--- |
| Quaker State 4x4* |
135 |
430 |
-35 |
--- |
--- |
| Red Line |
139 |
475 |
-40 |
--- |
--- |
| Shell Fire and Ice* |
155 |
410 |
-35 |
.9 |
.12 |
| Shell Rotella w/XLA* |
155 |
405 |
-37 |
1.0 |
.12 |
| Shell Truck Guard* |
155 |
405 |
-35 |
1.0 |
.12 |
| 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 DuraBlend |
142 |
440 |
-27 |
<1.5 |
.125 |
| Valvoline Synthetic |
140 |
450 |
-40 |
<1.5 |
.12 |
5W-30
| AMSOIL* |
173 |
464 |
-76 |
--- |
--- |
| Castrol GTX |
156 |
400 |
-35 |
.80 |
.12 |
| Chevron Supreme* |
167 |
410 |
-38 |
<1 |
--- |
| Chevron Supreme Synt.* |
169 |
468 |
-49 |
--- |
--- |
| 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* |
155 |
405 |
-35 |
--- |
--- |
| Quaker State Synquest* |
168 |
450 |
-58 |
--- |
--- |
| 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 DuraBlend |
162 |
415 |
-38 |
<1.5 |
.125 |
| 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 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.
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 exterme 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. 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 edh@maxey.dri.edu The Desert Research Institute
DoD #0200 WMTC BMWRA DIOC Reno, Nevada (702) 673-7380 |
