Date: Wed, 3 Apr 1996 16:32:53 CST6CDT
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: "Dan Houg" <fairwind@northernnet.com>
Subject: *very long* All you need to know on Synthetic oil
MODERN SYNTHETIC LUBRICANTS FOR
ENGINE OIL APPLICATIONS
By: Richard G. Golembiewski, P.E.
RIS Technical Editor
MILWAUKEE, WI - RIS - There's been a great deal of inter- est, of late, in the performance of synthetic
lubricants. Manu- facturers have enticed the motoring public for a number of years now, with claims for
increased fuel economy, reductions in fric- tion and wear, decreased oil consumption, better cold cranking
performance, and extended drain intervals. Many motorists howev- er, remain skeptical, as the price of
synthetics is usually much higher than conventional petroleum based oils. In addition, a great deal if
misinformation has circulated regarding them. Are these claims simply hype, or is there something here that
the average motorist can be interested in? Let's take a look.
Synthetic lubricants have been around for a long time. Synthesized compounds are the only thing that will
continue to flow at the low temperatures found in the arctic or in outer space. During the past twenty
years, some of these same benefits have been made available to the general public. In order to properly
examine the role synthetic lubricants play, and their performance, we need to first look at the fundamentals
of hydro- dynamic lubrication and lubricant properties and production.
Fundamentals of Hydrodynamic Lubrication:
As usually stated in engineering texts, and intuitively grasped by most laymen, a lubricant is inserted
between two moving surfaces to reduce friction, and the resultant generation of heat and wear.
"Hydrodynamic" lubrication exists when two surfaces are separated by a relatively thick film of lubricant.
A high pres- sure is not required to separate the surfaces. In a typical engine, plain or grooved journal
bearings are used to hold the crankshaft, piston rods, camshafts, and other machine components.
Take out a deck of cards. Place the deck on a table, and with your hand, move the deck horizontally.
Notice how the bottom card does not move, while the top card moves the most. Those in between move
too, with the amount of motion dependant on the height from the table.
What's happening here is that the friction between the table and the bottom card keeps it from moving. In
fluid mechan- ics, we refer to the layer that doesn't move as the boundary layer. The type of stress you
applied to the cards is called a "shear stress", and is equal to the horizontal force you applied divided by
the flat area of a card. This shear stress also af- fects the velocity of each card. This relationship is directly
proportional to the shear stress, and the distance from the table, and inversely proportional to a quantity
we will call the "viscosity". (Actually, it's a bit more complicated than this, but it's a suitable simplification
for our purposes.)
What this simply means is that for a given distance from one surface, the velocity will be lower if the
lubricant has a higher viscosity, and a constant shear stress is applied. Hence, the viscosity is a
measurement of the internal friction of the fluid, and its resistance to motion.
Our example used cards, but fluids are often modeled as infinitely thin layers. Thus if you drop a steel ball
into a glass of molasses (a high viscosity fluid) it will drop slowly because of the internal friction of the fluid.
Likewise, dropping the same steel ball in a glass of water, will cause it to drop rapidly because the fluid
does not have a particularly high viscosity.
We will not consider the methods used to measure viscosi- ty, but rest assured that standard methods
have been developed.
One of the problems with this internal friction is that it produces heat. If we model the fluid molecules as a
series of balls connected by springs, transfer of momentum takes place between the molecules and the
amplitude of vibration becomes greater. This means that it takes longer for one molecule to randomly
strike another, reducing the internal friction, and hence the viscosity.
This means that the viscosity of a fluid generally de- creases with temperature, and increases as the
temperature drops. If a fluid's viscosity is a function only of temperature, then it is characterized as
"Newtonian" after Isaac Newton. Unfortunate- ly, the viscosity of many fluids, engine oils among them,
drop with high shear rates. Such fluids are termed non-Newtonian.
OK, so what's the fluid's internal friction got to do with the friction between a pair of parts, such as a
crankshaft and a bearing? Plenty!
First, we need to differentiate between thin-film and thick-film lubrication. Thin films are a problem. as the
viscosi- ty decreases, the lubricant is less able to withstand the loads placed on it. Heat is generated,
reducing the viscosity even further. Surface-to-surface contact may occur. In thin films, the coefficient of
friction between the two surfaces actually goes up as the viscosity decreases. Such films are termed
"unstable". It is essential then to provide a film which is sufficiently thick to provide proper lubrication.
If the film is thick enough, however, the coefficient of friction between the mating surfaces actually goes
down as the viscosity of the lubricant drops. The temperature drops, and the viscosity of the fluid rises
slightly. This acts as a stabilizing effect, and prevents loss of film thickness.
The designer then, needs to specify the bearing/journal design and lubricant viscosity (for a given speed) in
such a way as to prevent the formation of a thin film. This means that the viscosity has to be high enough
even at high temperatures. Howev- er, the fluid still needs to flow at lower temperatures, and there is
enough reduction in friction between mating surfaces at moderately low viscosities to warrant their
selection.
As an aside, the temperature rise can be controlled some- what by providing a constant flow of oil to and
from the bear- ings. While the temperature in the sump (where we usually measure it) seems high, it's
significantly lower than at the contact surfaces themselves, and enough heat can be transferred to make a
recirculating flow system desirable. If temperatures become too high, then an additional cooler can be
added.
Lubricating Oil Fundamentals:
So what about the lubricant itself? What kind of specifi- cations does it have to meet? The American
Petroleum Institute (API), the American Society for Testing Materials (ASTM), and the Society of
Automotive Engineers (SAE) have cooperatively de- veloped specifications for lubricating oils.
If you take a look at the top of a motor oil can, you'll find the following: SAE viscosity specification (such
as 5W-30, which means that it is a multi-vis oil that meets both the 5W and 30 specifications.), an API
service classification (such as SF/CD), and perhaps an "energy conserving" designation.
The SAE viscosity designation, means that the oil meets SAE J300 specifications for cold cranking (if a
"W" rated oil) and at 100 degrees Celsius (if without a "W" rating), when proper ASTM testing
procedures are followed.
The API service classification is a bit more complex. You see, an oil may initially meet the SAE viscosity
specification, but when run at high temperatures for a period of time, its performance may deteriorate. The
API classifications for most engine oils are set for spark-ignition engines (such as SF, where the "F" is a
chronological designation), and compression-ignition (diesel) engines (such as CD). Several test sequences
are run using a standard engine. For instance, rust and number of stuck lifters are rated, the viscosity
increase over time (we'll talk about why this happens later) at, say 100 degrees F is measured, and the
amount of sludge, varnish, oil screen clogging, and cam lobe wear is estimated or measured.
These classifications are getting tougher. For instance, the SE rating for 1972 model cars allowed a
maximum of 400% increase in the oil's viscosity when measured at 100 degrees F after 40 hours.
However, the SF classification for 1980 model cars, allowed a maximum of 375% increase in the viscosity
when measured at 40 degrees C after 64 hours, with subsequent reduc- tions in the other categories. The
new SG rating is even tougher.
An engine may be designated as "energy saving" if they demonstrate reduced fuel consumption when
compared to an SAE 20W- 30 Newtonian reference oil. With the coming of federally mandated CAFE
requirements, most manufacturers are designating this type of oil for use in late model engines, and the
EPA allows their use.
Just what does an oil consist of, and how can it be com- pounded to meet these specifications?
Let's look first at conventional oils.
Crude oil as it comes from the ground is made up of a number of hydrocarbon compounds - primarily
paraffins, but it also includes other compounds. Often, these compounds are sepa- rated by viscosity
through a distillation process. Since differ- ent fractions of the crude have different boiling points as well as
different viscosities, progressive boiling is used. Those fractions with lower boiling points are allowed to
vaporize, and are collected and then cooled. These neutral fractions typically have lower viscosities, while
the bright stocks (those with higher boiling points) generally have higher viscosities.
As such, we can separate oils by viscosity.
But here's a problem. If we compound an oil to have a relatively low viscosity (or a multi-vis oil with a
significant amount of these lower boiling point/lower viscosity stocks) some of them will vaporize at high
temperatures, resulting in higher oil consumption. What's left behind has a higher viscosity. Varnish and
sludge are also present. If the decrease in viscosi- ty, amount of sludge, varnish, and cam lobe wear are
too high, it fails the API service test.
That's why a 5W-30 oil that meets the SF rating represents a major step. Those oils are said to be "energy
saving" since their lower viscosity at lower temperatures (with thick-film lubrication. Remember, if the
viscosity is too low, surface-to- surface contact may occur resulting in increased friction and wear!) results
in lower part-to-part friction. Yet by passing the SF rating, it shows that it's still pretty good.
Now, there are many things in the average motor oil than various refined fractions of crude. Included are
various addi- tives, such as anti-wear agents, extreme pressure (EP) additives, anti-rust agents, corrosion
inhibitors, detergents, dispersants, and friction modifiers.
Most of these are self-explanitory. They are added to enhance the performance of an oil. The EP additives
are put in to help the oil hold up between surfaces which feature high contact stresses such as those
between the cam lobes and followers. Detergents and dispersants are put in to help remove dirt and
sludge and hold it in suspension, until it's either removed in the filter, or the oil is changed.
Also included are various oil modifiers such as pour point depressants, viscosity index (VI) improvers, and
seal swell agents.
Pour point depressants are added to inhibit wax crystal growth at low temperatures. This gives the oil
better cold crank- ing performance.
VI improvers are designed to help an oil's viscosity/temperature performance. Remember that at high
tempera- tures, an oil's viscosity drops. If it drops too low, we lose film thickness, and are in big trouble!
The viscosity index (VI) is a measurement of how an oil's viscosity changes with tempera- ture, compared
to reference oils. The higher the number, the better. VI improvers are polymer compounds with
interlocking structures (polymers are long chain molecules). Because these chains are interlocked, they
don't move as easily at high temper- atures and resist viscosity loss. Unfortunately, they don't necessarily
contribute anything to lubricity, and in fact begin to wear out under shear stresses. As they wear, the oil's
VI deteriorates, and we're left with the old VI improver, which has to be held in suspension. This is
another reason to change your oil frequently! The VI improver's sensitivity to high shear stress is significant
in that if the shear stress is high enough, the oil may experience either a temporary or permanent loss of
viscosity!
Finally, an oil company may add various compounds which help protect the base stock, such as anti-foam
agents, antioxi- dants, and metal deactivators. The antioxidants are important as they prevent the oil from
reacting with oxygen at high tempera- tures and forming sludge, varnish, and lacquer.
So where do synthetics fit in? What are they? The term "synthesize" means to put together from small bits.
Rather than separating crude into various fractions as is done with conven- tional oils, synthetic base
stocks are made by reacting various organic chemicals together. For instance, if an acid an an alco- hol
are allowed to react, a compound known as an ester is pro- duced. (As an aside, the aroma present in
flowers is generally produced by an ester. Others include butter, lard, tallow, lin- seed, cottonseed, and
olive oils - although I wouldn't substitute my favorite engine oil for any of them in my cooking, or vice-
versa!) Other synthetic hydrocarbon compounds are also suitable for lubricating oils, and manufacturers
may blend two or more compounds together to arrive at suitable properties.
It should be noted that many additives are also made of synthesized compounds.
First, though, let's compare a conventional oil to a synthetic. A synthetic may require considerably less VI
improver to have the same viscosity index. Remember that the VI improver wears out. Synthetic's are also
more thermally stable.
Synthetic base stocks also have lower pour points - often below -50 degrees F, and require little or no
pour point depres- sant. In contrast, bright stocks may stop pouring at 25-30 de- grees F, and need it.
Still, synthetics are a bit more expensive, so compounding one to compete directly with a conventional oil
may not make economic sense. That's why they are usually made to have superior properties. The extra
performance is often worth the cost penal- ty.
For instance, synthetics can be compounded with very low pour points. This gives good cold-cranking
performance. They may also be compounded with slightly lower viscosities at lower temperatures (while
still meeting SAE specifications). This helps to reduce friction, and results in less wear, and better fuel
economy.
Now the 5W-30 "energy saving" oils will do the same thing, but as we've discussed before, to lower the
viscosity, these oils may be compounded with fractions which have a higher volatility. After a period of
time, they begin to boil off or oxidize, leav- ing behind an oil of higher viscosity. Now, that same oil may
meet API SF specifications, but a synthetic may remain stable for a LONGER period of time. (Esters
exhibit excellent performance in the API test. Other compounds are very, very good also.) That means
that longer drain intervals are possible.
A word on use. Some synthetic compounds are not compatible with conventional oils. However, most
manufacturers, have recog- nized that one may add a quart of their product to someone else's, and have
compounded them to be. To do otherwise would be to pass up their intended market! (As an aside, I try
to avoid having to mix conventional oil, if I can help it. While they are also compounded to be compatible,
the performance may not be the same when mixed together. It's ok in a pinch, but I don't make a habit of
it.) Also, the lower friction resulting from the use of a synthetic lubricant makes them unsuitable for
break-in.
To sum up, synthetics provide an excellent alternative to conventional oils - especially if better
performance is required. It's your choice!
All About Lubricants
>From a talk to Dema Elgin's High Performance Engine Class
DeAnza College, Cupertino, California
By Roy Howell, Chief Chemist, Redline Synthetic Oil Company
Formerly of Lubrisol
Talk given 07 April 1992
Notes taken by Jack L. Poller
Notes not presented in any particular order
Basis of Lubricants
1) Separate Surfaces 2) Removal of Heat (up to 1/3 of combustion heat may be transferred away
from engine by oil) 3) Containment of Contaminants 4) Sealing
Refining of Crude Oil into a Lubricant
1) Refining is the process of removing all the bad stuff. The bad stuff is primarily oxidants. The result of
oxidation of the lubricant is first varnish, then it polymerizes into 'goop'. (SA grade oil will goop in 5000
miles)
2) Add Oxidation Inhibitors.
3) Add Detergents. Reacts with oxidized material. Helps keep piston rings clean (Rings are quite hot).
Leaves an ash residue when combusted. Not used in airplane engine oils.
In an automobile engine, the piston speed (RPM) and therefore piston tempature changes greatly and
quickly. The tempature differences allow the ash to break up into small deposits, and go into the exhaust
or blow by the rings into the crankcase and lubricants.
In an airplane engine, the pistons are operating continuously at a single speed, and therefore do not go
through heating and cooling cycles, so the ash deposits would not break up.
Generally, for automobile motor, lubricant is limited to 1% ash content. 2% ash is asking for trouble
(although 2% may be okay for a diesel engine). Red Line Racing Oils are low detergent. Detergent is left
out because ash can cause detonation.
4) Add Dispersants. Dispersants are ashless detergents, which complex low temperature combustion
byproducts. Dispersants keep partially oxidized particles in suspension, and help keep the engine clean.
Dispersants can come apart in exterme high temperature.
Average oil filter is a 20 micron filter. Could go down to 1 micron. Stuff that dispersant holds in
suspension is much less than microns (it is measured at the molecular level, in Angstroms). At proper
temperature, the stuff is not really a problem. Most of the stuff is Aromatic Hydrocarbons, boil around
180 F, and leave through crankcase ventilation.
5) Add Anti-Wear additives. These additives chemically react with iron to prevent welding of moving
metal surfaces. Most common additive is ZDP, or Zinc Dialkyl Dithio Phosphate. What happens is
essentially a chemical polishing of the metal surface.
The surface gets plated with either Iron Phosphate or Iron Sulfate, both of which are softer than the base
Iron. This chemical reaction occurs in the 300 to 400 F range, and the Zinc is a temperature controlling
carrier (controls the temperature at which the reaction occurs. When the two metal surfaces come in
contact, a small amount of the surface plating is 'scraped' off of the surface. This is replenished by more
ZDP contact with the metal. This action prevents the metals welding through heat generated by high
friction contact. The ZDP in the lubricant may last up to 20,000 miles.
6) Add AntiFoam. Anti foam is a surfactant, usually silicone, and weakens bubbles.
Synthetic Lubricants
Major Difference is synthetics are not petroleum based.
Key Advantages
1) Volitility: Synthetics do not evaporate as readilly as Petro. based. Usually, synthetic lubricants are
based on 1 molecule with a flat distillation curve.
2) Better viscosity versus temperature behavior Thin less as they get hot Thicken less as they cool
3) better oxidation stability
4) Synthetic Oil has 10% better heat transfer than Petrolium based lubricants.
Viscosity Index Improvers
Rubber and Plastic Polymers
Start with a base of straight weight Oil. Then add a polymeric thickener. When hot, the long polymer chain
is really moving around, causing the oil to flow less. When cold, the polymers stick to each other,
essentially comming out of suspension. The polymers are stable up to about 210 F, where they start to
break up. The drawbacks to VI polymers is that they can cause engine dirt because of their low shear
strength.
Viscosity A B C D
High | ' ' ' '
| ' ' ' '
|* ' ' ' '
| \ ' ' ' '
| *- ' ' ' '
| *\ ' ' ' '
| *- ' ' ' '
| *\' ' ' '
| *- ' ' '
| ' *\ ' ' '
|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| ' *-*\ ' ' '
| ' *\*-*\*-*\*-*\*-*\*-*\*-*\*-*\*-*\
| ' ' ' '
Low |_____________________________________________________________
Low High
Sheer Rate
A Shear at Piston Rings
B Shear at Main Bearings
C Shear at Cylinder Wall
D Shear at Connecting Rod Bearings
-+-+ Viscosity of a Straight Weight Oil (Petro. Or Synthetic)
*\*- Viscosity of A MultiGrade Oil (Base with VI polymers)
What this chart shows is that a straight oil has the same viscosity regardless of shear rate. However, as the
shear rate increases, the shear breaks down the VI polymers, and multigrade oils have less actual viscosity
at the localized high shear rate area.
The weak link is the rod bearings and Cam, in terms of rate of shear. There is less friction at the piston
rings. Anti Wear is much more important at the cam.
Coolant
Red Line Water Wetter is a surfactant - reduces the surface tension of the water. Allows the water to
more intimately contact metal. When the water boils, the surfactant makes smaller bubbles, which makes it
easier for the bubble to be pushed away from the metal surface, and allow more water to contact the
metal.
Water Wetter has a high Ph, but also has silicates, so it can be used in aluminium radiators. However, if
left for a long time, the silicates are depleted, and damage will occur. The liquid versions of Water Wetter
do not have phosphates.
Discovered by Roy Howell. Some engineers were begging Roy to develop a corrosion inhibitor to add to
straight water for racers, since racers rarely use AntiFreeze. He did some work, developed Water Wetter
simply as a corrosion inhibitor, and gave it to Huffaker. Huffaker immediately n
oticed lower operating
temperatures, and Roy started to investigate why.
You *can* cool an engine to much. The ideal temperature for coolant is 190 F.
AntiFreeze has 1/4 heat transfer capability of straight water.
Temperature recordings at block water jacket exit, after stabilizing:
Water Anti-Freeze Water Wetter Temperature (F)
50% 50% No 228
50% 50% Yes 220
100% 0% No 220
100% 0% Yes 202
Differences between RedLine and Mobil 1 Redline starts out with a Jet Turbine Oil Base, which has a
higher level of thermal stability, and they have to add less friction modifiers.
Red Line has 1/2 Cf of Mobil 1.
Viscosity vs. Sheer strength are similar, but Red Line handles high loads better.
Can gain 1 - 2% more power by going to a lower viscosity oil.
There is no longer a problem with synthetic lubricants eating away seals. (Original Mobil-1, no longer
available, left out seal-swell).
Red Line blends its lubricants, but does not manufacture the synthetic bases.
Molybdenum in CV Joint Lube
Molybdenum in CV joint lube is important in high-angle CV joints, especially off-road applications, where
wet lub may be thrown from contact area. The moly provides a dry-film lubrication.
Gear Oil
Gear oil viscosity is measured at 150 F vs. 210 F for motor oil. Therefore, 40 W motor oil is the same as
95 W gear oil.
Gear oil is acidic, motor oil is alkiline. Gear oil needs very high wear protoection - Extreme Pressure
(marked as EP). Therefore, it has a very high sulfer and phospor content. Sulfur and Phosphate reactions
start at a lower temperature, and Gear Oil has much more additive than motor oil. This additive is
corrosive to copper bearings and bronze synchro rings.
Positraction additives are Friction modifiers - make the base oil much more slippery. They coat the metal
surfaces, and prevent the stick/slip mode of operation, preventing shudder, and causes smoother take-up.
Friction Modifiers may detract from EP characteristics.
Friction modifiers cause smooth take-up of Limited slip units. For track racing, FM is probably
undesireable, and immediate take-up is more important. For Street, FM is usually reccomended for more
comfortable operation.
Gear oils decompose at lower temperature, usually 250 F.
Gear Lubrication Ratings
GL-1 No Additives
GL-2
GL-3
GL-4 Suitable for light duty hypoid sets
GL-5 Has lots of sulfer - Heavy duty hypoids
GL-6
Hypoid type gear sets have a sliding rather than rolling action, and therefore require much greater wear
protection.
GL-5 Should be used in rear differentials.
GL-6 is a heavier weight GL-5. Used for heavy trucks and Tow Vehicles.
Red Line 75 - 90 NS has No Slip, i.e., no Friction Modifiers.
Red Line 75 - 90 has Friction Modifiers.
Gear mesh in Gears litterally chops up and cuts appart the long polymer chains of Viscosity Index
improvers.
Smell of gear oil is from high sulfur content.
Quaiff Differential is a worm gear, and needs a very slippery oil.
ATF
Type F - no Friction Modifiers. Ford originally did not want slip in clutch plates.
Dexron - GM - less Cf than Type F
Now Mercon and Dexron II are almost identical.
Reccomendations
Red Line does not reccomend DOT-5 Brake Fluid for racing. More compressible at temperature.
Red Line does not reccomend mixing race oil with regular oil.
Red Line reccomends breaking in an engine on straight viscosity oil.
Can not use silicone brake fluid in ABS systems, as there is no lubrication for ABS pump.
Can use Race Oil for 3 to 4 Events.
Bearing Grease
Dont fully pack the hub, as it will just overflow. As it turns, the bearing cust the grease, and oil leaks out.
This oil then provides the lubrication.
Slick 50
Lubrisol, Dema Elgin, a Ford Engineer all agree that it does not do anything. According to Roy, to plate
teflon on a metal needs an absolutely clean, high temperature surface, in a vacuum. Therefore, it is highly
unlikely that the teflon in slick 50 actually plates the metal surface. In addition the Cf (Coefficient of
friction) of Teflon is actually greater than the Cf of an Oil Film on Steel. Also, if the teflon did fill in 'craters'
in the steel, than it would fill in the honing of the cylinder, and the oil would not seal the piston rings.
Phomblin
Phomblin (Another chemical similar to Teflon, used in polishes) is a flouridated ether, has low valitility, is
very inert, has low surface tension, and is very expensive. Owned by MontEdison.
Miscellaneous
Red Line SI-1 - Injector and Valve Cleaner - Removes approximately 1/2 deposits on valve with each
bottle.
STP is a VI.
Castrol R is Castor Oil based. Good lubrication, but dirty.
Methyl Lead goes to intake faster than Ethyl Lead. EPA now has authority to outlaw lead entirely.
Marvel Mystery Oil and Rislone are surfactants and penetrants.
Neo and other Zero Weight oils are actually 0W - 20 multigrade oils, so as soon as they warm up, they
are effectively 20 weight oil.
Engine Temperature Chart (F)
Upper Cylinder Wall 300 - 500
Exhaust Valve 1200 - 1500
Piston Crown 700 - 800
Hydraulic Valve Lifter 250 - 300
Crankcase 200 - 300
Top Ring 300 - 650
Exhaust Gases 500 - 1000
Combustion Chamber 3000 - 5000
Coolant Jacket 165 - 230
Connecting Rod Bearings 200 - 375
Main Bearings 200 - 350
Motor Oil Limits (F)
700 -------------------------------------------------------------
|
600 Maximum Useful Range of All Proof Synthetic Motor Oil |
|
500 ------------------------------------------------ |
--------------------------------- Maximum | |
400 ----------------| | Useful | |
Maximum Useful | Maximum | Range of | |
300 Range of | Useful | Diester | |
Premium | Range of | Synthetic | |
200 Petroleum | Polyolefins | Motor Oils | |
Motor Oils | | | |
100 | | | |
| | | |
0_______________________|_______________|_______________|___________|
