all about viscosity


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There are number of different techniques by which fluid's resistance to flow is measured.

Because Viscosity changes with temperature and sometimes also with pressure, it is alsoimportant that when different fluids are compared that the measurements were conductedunder the same temperature and pressure conditions.

The common metric unit of absolute viscosity is the poise.

For convenience, the CentiPoise (cP) [one one-hundredth of a poise] is the unit customarilyused.

Laboratory measurements of viscosity normally use the force of gravity to produce flowthrough a capillary tube ( viscometer ) at a controlled temperature. This measurement iscalled kinematic viscosity .

The more customary unit is the centistoke (cSt) [one one-hundredth of a stoke].

VISCOSITY - General

We are accustomed to the notion of friction as a force that is exerted opposite to that whichbrings about motion when one solid moves in contact with another.

Such friction force tends to slow and eventually stop movement, unless the propulsive forceis maintained so that the friction force is equalized.

There is also a friction where solid moves through liquid, as when ship plows through water.The ship once set in motion will come to halt; unless the propulsive force is maintained heretoo. Although water seems so smooth and lacking any projection to catch the ship, waternevertheless absorbs enough energy when it is pushed apart by the ship to eventually stopit.

This friction arises from the fact that it is necessary to expend energy (power) to pull thewater apart against its own cohesive forces in order to make room for the ship to pass

through it.

The energy expanded varies greatly with the shape of the object that passes through thefluid.

If the fluid is pulled apart gently and gradually, and then brought back even more gently andgradually, then the energy needed to be expanded is minimal.

Such action is possible only by object that is of teardrop shape.

By contrast if the fluid is pulled apart abruptly in such a way as to force it into eddies andother turbulence , such as by cube, the maximum energy will have to be expanded to move

the cube through the fluid.The friction between a moving solid and a surrounding liquid increases with velocity, so nomatter how streamlined the object may be, eventually a terminal velocity will be reachedand thus and object falling through the water accelerated by gravitational pull, willeventually fall at a constant speed.

Any object will sink faster in fluid of low viscosity such as water, and will sink much slower ina high viscosity fluid such as glycerin.

Viscosity of a fluid can thus be " measured " by the time it takes for object, such as a steelball bearing, fall through a test tube with oil, for example.


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Steel Ball fall speed is inversely proportional to Oil ViscosityFaster through less viscous oil; Slower through more viscous oil

The friction makes itself evident even when the liquid itself is the only substance involved.When any liquid moves, or pours, it does not move all-in-one as a solid does.

Instead, a given portion of the liquid will move relative to a neighboring portion and " internal friction " between these two portions will counter the motion. Where the cohesive forces thatimpose this internal friction are low, as in water, we are not ordinarily very aware of this.When the cohesive forces are high such as in cold honey, the fluid pours very slowly.

The internal friction for any fluid is higher at low temperature, and much lower at highertemperatures. So honey that was in refrigerator, will barely flow, but once warmed to roomtemperature will pour easily.

The difference in flow between freezing cold and boiling hot water however is so small as notbeing perceivable by human senses. However, very sophisticated laboratory equipment can

detect the difference.

Where the difference in flow between hot and cold fluid is very small, such fluid is said tohave HIGH VISCOSITY INDEX. (High VI)

By contrast honey will be solid at freezing and water like at boiling temperatures, such fluidis said to have LOW VISCOSITY INDEX. (Low VI)

At room temperature water has viscosity of just about ONE CentiPoise, while the commonanesthetic - diethyl ether has viscosity of 0.23 CentiPoise or 23 MilliPoise, and glycerol isabout 1,500 CentiPoise or 15 Poises.

The unit of viscosity the Poise has been named in honor of French physician Jean LouisPoiseuille (1799-1869), who in 1843 was the first to take time to study viscosity inquantitative manner.

As a physician he was interested in the manner in which blood moved through blood vessels.But his observations proved to be valid for ALL liquids.

For the purpose of lubrication, viscosity has been since the beginnings of LubricationEngineering held as the most important quality of the Lubricant.

The reason for this is that if the lubricant is too thin, it gets forced out from bearing surfaceunder pressure and poor lubrication occurs, this leads to bearing surface damage.

If the lubricant is too viscous, it either does not flow into the bearing surface, causing lubestarvation, and thus certain bearing damage. Or it consumes too much energy, which is thenconverted to heat and the bearing may be overheated, at which point it can seize due to lossof running clearance.

Therefore oil that is either too viscous or too thin, will cause premature failure of any


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bearing surface.

The proper viscosity for given application is therefore extremely important.

That is why the first lubricant standard J300 that was developed by SAE in 1911 wasViscosity Classification of Motor Oils , and although this standard was revised andupdated many times it is still used today world-wide for Motor Oil applications.

However unlike the exact scientific value of Poise for Absolute Viscosity, the SAE viscositynumbers are " staircase " approximations for KINEMATIC Viscosity.

For example Motor Oil that is measured to have viscosity of 9.5 cSt @ 100C will be rated asSAE 30 , while another Motor Oil that is measured to have viscosity of 12 cSt ( or 26% moreviscous ) will also be rated as SAE 30 Motor Oil.

Yet in real life operation 26% difference in viscosity may make difference between enginethat will run forever and one that will wear out prematurely.

That is why " stay in grade " over the service life of the Motor Oil is also important!

The SAE J300Standard is only relating to a FRESH UNUSED MOTOR OIL.

As few as 20 hours of operation will change viscosity of pure petroleum oil.

Some oils classified as SAE 30 when Fresh will with use and temperature shear and thin outto SAE 20 or below, while some other oils will oxidize and sludge up to become much moreviscous like SAE 40 or even SAE 60 !

The " best " motor oil will be SAE 30 when fresh and SAE 30 when drained out after its use,this is termed as " Stay in Grade ".

Motorists make the common mistake that every SAE 30 oil is the same in performance, butthe reality, however, is quite different.

Even more drastic differences in viscosity for fresh and used oils can be observed in multi-

viscosity or multi-grade oils such as SAE 5W-30 .

The SAE J300 Standard for viscosity classification of Motor Oil therefore should not beconfused with any level of quality or long term performance.

API Service Classifications are used to distinguish Motor Oil performance levels and arebased on specific engine and laboratory tests.

No matter what oil you use for any purpose the ideal viscosity that provides the ultimatelubrication, that is TOTAL bearing surface separation, and at MINIMUM power that isconsumed by the lubricants viscosity (MINIMUM TEMPERATURE RISE) occurs ONLY at ONEcombination of:

SPEEDLOADTEMPERATURE

Under ALL other combinations of the three factors, the lubricant is NOT IDEAL.

Some lubricants, due to much higher than normal viscosity index, can have moreadvantageous performance over much wider range of TEMPERATURE, SPEED and LOAD,than others and therefore can be used more universally in wide range of applications.

That is why some lubricants such as single grade SAE 30 , must be changed to SAE 20 whenoperating temperature is reduced or to SAE 40 or SAE 50 when the operating temperatureis increased.

So thicker more viscous oil is needed when engine is operated at higher temperature such ashigh summer heat.

Similarly the proper viscosity depends on Load , the higher the load the thicker or higherSAE number is required. Therefore on highly loaded engine designed to use SAE 30 oil


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under normal operation; SAE 40 or SAE 50 should be utilized.

Speed however has the opposite effect, when engine designed to run at 2,000 RPM isconstantly run at 6,000 RPM but at the same load, the SAE 30 oil should be substituted withSAE 20 oil. Higher operating speed requires thinner or lower viscosity lubricant.

It is possible in some applications that the increase in Load can be just offset by theincrease in Speed and then the same oil such as SAE 30 that is just right for NORMALoperation will be also JUST RIGHT for the new HIGH LOAD and HIGH SPEED regime.

"Old" truckers are well aware of this from experience, they get much better and longerengine life when running in lower gear up-hill. Extra LOAD is imposed on the engine byclimbing uphill (lifting cargo weight against the pull of gravity requires more power thereforethe engine LOAD is increased = this requires thicker lubricant), this can be balanced byrunning engine at much higher RPM (this requires thinner lubricant).

The alternative of running uphill in low gear, that is at slow engine speed and increased loadwould surely require increase in motor oil viscosity or else almost certain engine damagewould result.

It would be rather inconvenient to change motor oil before and after every major hill on theInterstate. Therefore changing gears is much more feasible.

Thinner motor oils such as SAE 5W-20 or even SAE 0W-20 are becoming more popularthese days and were specified by some OEM's (FORD & HONDA) on new cars since 2001Model Year.

Although these oils are promoted as " energy conserving " they generally trade a gain of lessthan 0.1 MPG in Corporate Average Fuel Economy (CAFE) for shorter useful engine life.

FORD which has previously designed cars to have 10 year or 150,000 miles life has reducedthe mileage life expectation to "beyond 100,000 miles" on vehicles that are operated on SAE5W-20 Motor Oil.

HONDA only claims " useful life " as 7-years or 70,000 miles in EPA certifications for theirCIVIC which uses SAE 5W-20 Motor Oil, while the previous model year that utilized SAE5W-30 Motor Oil was certified for 10 year or 100,000 mile durability.

Since both HONDA and FORD Warranty their NEW cars for ONLY 3-years or 36,000-milesthe reduction in engine life expectancy is not a factor.

By contrast Mercedes-Benz recommends use of ONLY Synthetic Motor Oil that is at leastSAE 5W-40 !

This is a recent increase in recommended viscosity from SAE 5W-30 . Apparently customerresearch indicated that engine longevity is more important to typical MB customer than fueleconomy.

Similarly BMW specifies the use of Synthetic Motor Oil that has a rating of SAE 10W-60 !This is for use in some of their high performance engines.As a result BMW has to pay annually CAFE fines ranging in millions of dollars, but theyconsider this as "cost of doing a business in USA".

Apparently customer research again indicated that engine reliability is more important totypical BMW customer than fuel economy.

Even more important is the High-Shear High-Temperature MINIMUM specification in SAEJ300 .In tables below you will notice that there are "two" SAE 40 specifications, one with minimumHSHT value of 2.9 cP for Automotive Oils (SAE 0W-40; 5W-40; 10W-40) and the other forHeavy Duty Oils (HDO) (SAE 15W-40; 20W-40; 25W-40; 40).

This double specification is at insistence of heavy duty engine manufacturers who haverequired HSHT viscosity limits consistent with good engine durability in high-load, severeservice operation.HSHT value of 3.7 cP or 27% more viscous oil at 150C (300F).


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Yes, a 27% increase in viscosity makes a difference between Automotive engine that lasts100,000 miles and Truck engine that lasts 1,000,000 miles!

When you consider that most Automotive Motor Oils are ONLY 3 cP, while ourSynLube Lube4Life Motor Oil has rating of 5 cP, you can readily appreciate why we canclaim 300% to 500% increase in typical Automotive engine durability, and that is withsubstantial " safety " reserve!

If you wish to learn more about viscosity, following definitions which are also mirrored in ourGLOSSARY should give you more technical know-how than you ever dreamed possible!

DEFINITIONS

Viscosity

The measure of the internal friction or the resistance to flow a liquid.Low viscosity fluids flow easily (water);High viscosity fluids pour slowly (molasses).

Measurement of a fluid's resistance to flow. The common metric unit of absolute viscosity isthe poise, which is defined as the force in dynes required to move a surface one squarecentimeter in area past a parallel surface at a speed of one centimeter per second, with thesurfaces separated by a fluid film one centimeter thick. For convenience, the CentiPoise (cP)[one one-hundredth of a poise] is the unit customarily used.

Laboratory measurements of viscosity normally use the force of gravity to produce flowthrough a capillary tube ( viscometer ) at a controlled temperature. This measurement iscalled kinematic viscosity .

The unit of kinematic viscosity is the stoke , expressed in square centimeters per second.The more customary unit is the centistoke (cSt) [one one-hundredth of a stoke].

Kinematic viscosity can be related to absolute viscosity by the equation:

cSt = cP * fluid density

In addition to kinematic viscosity, there are other methods for determining viscosity,including:

Saybolt Universal SecondsSaybolt Furol ViscosityEngler DegreeRedwood Viscosity .

Since viscosity varies inversely with temperature, its value is meaningless unless thetemperature at which it is determined is reported.

See: viscosity index , viscosity-temperature relationship ,

Absolute Viscosity

The ratio of shear stress to shear rate .

It is a fluid's internal resistance to flow.

The common unit of absolute viscosity is the poise and CentiPoise cP (see viscosity ).

Absolute viscosity divided by the fluid's density equals kinematic viscosity .

Absolute Viscosity is the tangential force per unit area of two parallel planes at unit distance


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apart when the space between them is filled with a fluid and one plane moves with unitvelocity in its own plane relative to the other.

Absolute viscosity is also known as " coefficient of viscosity ".

Absolute viscosity is typically measured by a rotary viscometers to determine the torque onrotating spindle and so measure the fluid's shear resistance. Changing the rotor (spindle)dimensions and the gap between the rotor and stator wall (container) and the speed of rotation can change the rate of shear.

Examples of rotary viscometers that are used for Absolute Viscosity measurements:Cold Cranking Simulator (CCS)Mini-Rotary Viscometer (MRV)Brookfield ViscometerTapered Bearing Simulator

In relation to oils for Automotive applications such as Motor Oil or Gear Oil, the CCS andMRV test equipment at low temperatures is used to determine if the test lubricant does notget too thick to prevent safe engine or transmission operation at low temperatures.

If Motor Oil is too viscous to flow, even if engine can be started, certain mechanical damagewill result due to localized oil starvation. In transmissions both manual and automatic, propershifting may be impaired, affecting safe vehicle operation once vehicle is put in motion.

In the new SI system, it is proposed that values for the Poise be stated as Pascalseconds .

The conversion factor being:

1 Poise equal to 1x10 -1 Pas.

A common measurement unit is the milliPascal second (mPas).

Conversion factors are as follows:

1 centipoise (cP) = 0.01 poise (P)

1 Pas = 10 P

1 cP = 0.001 Pas = 1 mPas

1 Pas = 1000 cP

Apparent Viscosity

The ratio of shear stress to rate of shear of a non-Newtonian fluid such as lubricatinggrease, or a multi-grade oil, calculated from Poiseuille's equation and measured in poises.

The apparent viscosity changes with changing rates of shear and temperature and must,therefore, be reported as the value at a given shear rate and temperature (ASTM Method D1092).

Apparent Viscosity is value obtained by applying the instrumental equations used inobtaining the viscosity of a Newtonian fluid to viscometer measurements of a non-Newtonianfluid.

Kinematic Viscosity [mm 2/s = cSt]

Absolute viscosity of a fluid divided by its density at the same temperature of measurement.


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It is the measure of a fluid's resistance to flow under gravity, as determined by test methodASTM D 445.

To determine kinematic viscosity , a fixed volume of the test fluid is allowed to flow through acalibrated capillary tube ( viscometer ) that is held at a closely controlled temperature.

The kinematic viscosity, in centistokes (cSt), is the product of the measured flow time inseconds and the calibration constant of the viscometer.

The kinematic viscosity is the quotient of the dynamic viscosity and the fluid density ,

=/

The physical principle of measurement is based on the rate at which a fluid flows undergravity through a capillary tube viscometer.

Measured in stokes (St) or centistokes (cSt). One centistoke = 0.01 stokes.

The metric unit is square meters per second (m 2 /s).

Kinematic Viscosity conversion factors

ConvertFROM

ConvertTO Multiply by

cSt m2 /s 0.000001

St m2 /s 0.000100

cm 2 /s m2 /s 0.000100

ft2 /h m2 /s 2.580640

ft2 /s m2 /s 9.290300

in 2 /h m2 /s 1.792110

in 2 /s m2 /s 6.451600

m2 /h m2 /s 2.777780


1 St = 1 x 10 -4 m 2 /s

1 m2 /s = 10,000 St

1 cSt = 1 x 10 -6 m 2 /s = 1 mm 2 /s

1 m 2 /s = 1,000,000 cSt

Centistokes may be converted to centipoise (cP) by multiplying by the density of the fluidbeing measured, both measured at the same temperature.

Dynamic viscosity [mPas = cP]

The dynamic viscosity is the viscosity that relates shear stress and shear rate du/dz in afluid:


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= du/dz

The viscous shear stress is proportional to the shear rate, the dynamic viscosity beingthe proportionality factor.

So, thicker oils have a higher viscosity value causing relatively higher shear stresses at thesame shear rate.

Dynamic viscosities are usually measured under high shear conditions, for example, the coneon plate or cylinder viscometer in which the viscous shear torque is measured between twocylinders.

The SI derived unit for dynamic viscosity is:Newton second per square meter (Ns/m 2 ) = 1 Pascal second (Pas)

Dynamic Viscosity conversion factors

ConvertFROM

ConvertTO Multiply by

cP Pas 0.00100

P Pas 0.10000

dyns/cm 2 Pas 0.10000

gfs/cm 2 Pas 98.06650

g /(cms) Pas 0.10000

kgfs/cm 2 Pas 9.80665

kg/(ms) Pas 1.00000

Ns/m 2 Pas 1.00000

poiseuille Pas 1.00000

lbfs/ft 2 Pas 47.88030lbm/(fts) Pas 1.48816

lbm/(ins) Pas 17.85800

reyns Pas 1.48816

slug/(fts) Pas 47.88030

slug/(ins) Pas 574.56300


1 (Ns/m 2 ) = 1 (Pas) = 10 poise (P) = 1 dekapoise (dP)

9.806 65 kg = 1 kgf

VI (Viscosity Index)

An arbitrary scale used to show the magnitude of viscosity changes in lubricating oils withchanges in temperature.

Oils with low VI number such as VI=0 ("zero") have high dependence of viscosity change ontemperature. They thicken quickly with decreasing temperature, and thin out quickly with

increasing temperature.Oils with high VI number such as VI=200, will still thicken with decreasing temperature butnot as rapidly, and also will thin out with increasing temperature, but again not as much aslow VI oil.

Calculated VI number can also be " negative "


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Tables found in ASTM Method D 2270 are widely used to determine VI number.

However, VI does not tell the whole story -- it only reflects the viscosity/temperaturerelationship between temperatures of 40C and 100C.

Two lubricants or base oils with the same VI number may perform dramatically different atlow temperatures in the -5C to - 50C range.

In many cases the temperature dependency is expressed in the Viscosity Index standardizedby ISO 2909 / ASTM D2270-226.

Viscosity Index Improver (VII)

Chemical additive that is added to finished lubricants to improve the viscosity index .

Lubricant additive , usually a high-molecular-weight polymer , that reduces the tendency of anoil to change viscosity with temperature.Multi-grade oils , which provide effective lubrication over a broad temperature range, usuallycontain V.I. improver.

While Viscosity Index Improver can enhance viscosity index (VI), they can break down undershear or over time, resulting in diminished performance.

viscosity-temperature relationship

The manner in which the viscosity of a given fluid varies inversely with temperature.Because of the mathematical relationship that exists between these two variables, it ispossible to predict graphically the viscosity of a petroleum fluid at any temperature within alimited range if the viscosities at two other temperatures are known. The charts used for thispurpose are the ASTM Standard Viscosity-Temperature Charts for Liquid Petroleum Products,available in 6 ranges. If two known viscosity-temperature points of a fluid are located on thechart and a straight line drawn through them, other viscosity-temperature values of the fluidwill fall on this line; however, values near or below the cloud point of the oil may deviatefrom the straight-line relationship.

Viscous

Possessing viscosity. From the Latin word for a sticky species of birdlime that is a slowly-pouring liquid.Frequently used to imply high viscosity.

viscometer

Device for measuring viscosity ; commonly in the form of a calibrated capillary tube throughwhich a liquid is allowed to pass at a controlled temperature in a specified time period.


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Various types of Laboratory Viscometers

See kinematic viscosity , Saybolt Universal Viscosity .

SAE

The Society of Automotive Engineers (SAE) is an engineering society founded to develop,collect, and disseminate knowledge of mobility technology.

SAE

SAE J300 Viscosity Classification ( April 1997 )SAE Viscosity

GradeLow Temp.Cranking

Low Temp.Pumping

MinimumKinematic

MaximumKinematic

Hi-Temp.Hi-Shear

0W 3,250 @ -30 60,000 @ -40 3.8

5W 3,500 @ -25 60,000 @ -35 3.8

10W 3,500 @ -20 60,000 @ -30 4.1

15W 3,500 @ -15 60,000 @ -25 5.6

20W 4,500 @ -10 60,000 @ -20 5.6

25W 6,000 @ -5 60,000 @ -15 9.3

20 5.6 9.3 2.6

30 9.3 12.5 2.940 12.5 16.3 2.9

40 12.5 16.3 3.7

50 16.3 21.9 3.7

60 21.9 26.1 3.7

5W-50 3,500 @ -30 30,000 @ -40 16.9 18.0 5.0

The SAE 5W-50 rating shown above is for SynLube Lube4Life Motor Oil.

However, the previous specification has been revised by SAE in December 1999 to onetabulated below.

According to "new" J300 our existing version of SynLube Lube4Life Motor Oil shouldhave been classified as SAE 0W-50 , however our customer research has shown that thisunusual classification was " too radical " and " too scary ", so we have decided to retain ourexisting rating of SAE 5W-50 that was originated in 1985. This required slight " thickening "


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of the lubricant at low temperatures, achieved by only 2% increase of one of our existingingredients. By " missing " the target SAE 0W low temperature viscosity by50 cP at -40C we can " legally " label our lubricant as SAE 5W-50 , while for practicalpurpose offer to our customers cold performance that " almost matches " SAE 0W motor oil.

SAE J300 Viscosity Classification - Motor Oil ( January 2009 )

SAE ViscosityGrade

Low Temp.Cranking(mPa.s)

max at temp C

Low Temp.Pumping(mPa.s)

max at temp C

Minimum

Kinematic(mm 2 /s)at 100C

Maximum

Kinematic(mm 2 /s)at 100C

Hi-Temp.Hi-Shear(mPa.s)

at 150C @ 10/s

0W 6,200 @ -35 60,000 @ -40 3.8

5W 6,600 @ -30 60,000 @ -35 3.8

10W 7,000 @ -25 60,000 @ -30 4.1

15W 7,000 @ -20 60,000 @ -25 5.6

20W 9,500 @ -15 60,000 @ -20 5.6

25W 13,000 @ -10 60,000 @ -15 9.3

20 5.6 9.3 2.6

30 9.3 12.5 2.9

40 12.5 16.3 2.9

40 12.5 16.3 3.7

50 16.3 21.9 3.7

60 21.9 26.1 3.7

5W-50 6,250 @ -35 30,000 @ -40 16.9 18.0 5.0

The SAE 5W-50 rating shown above is for SynLube Lube4Life Motor Oil.

NEW - SAE J300 Viscosity Classification - Motor Oil( April 2013 )The new SAE 16 Viscosity has been approved for inclusion in a new version of the SAE J300Viscosity Classification that is planned to be published in April 2013.

The SAE 20 Viscosity Grade Minimum Kinematic Viscosity will be increased from the 5.6 mm 2

to 6.9 mm 2 .

The new SAE 16 grade will have minimal impact on the North American engine oil market,since it is being specified by only one automaker (Honda) for 2013 model year engines.However, the advantages in term of fuel economy will undoubtedly encourage other OEMs toevaluate SAE xW-16 engine oils in the future.

SAE ViscosityGrade

Low Temp.Cranking(mPa.s)

max at temp C

Low Temp.Pumping(mPa.s)

max at temp C

MinimumKinematic

(mm 2 /s)at 100C

MaximumKinematic

(mm 2 /s)at 100C

Hi-Temp.Hi-Shear(mPa.s)

at 150C @ 10/s

16 6.1 8.2 2.3

20 6.9 9.3 2.6

SAE Viscosity of Automotive Gear Oils - SAE J306( Jan 2005 )

SAEViscosity Grade

Maximum Temperaturefor a viscosity of 150,000 cP (C)

Minimum Viscosityat (cSt) a 100C

Maximum Viscosityat (cSt) a 100C

ASTM D 2983 ASTM D 445 ASTM D 445


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15 15 13.5 16.5 75

22 22 19.8 24.2 105

32 32 28.8 35.2 150

46 46 41.4 50.6 215

68 68 61.2 74.8 315

100 100 90 110 465

150 150 135 165 700

220 220 198 242 1000

320 320 288 352 1500

460 460 414 506 2150

680 680 612 748 3150

1000 1000 900 1100 4650

1500 1500 1350 1650 7000

The SAE 5W-50 SynLube Lube4Life Motor Oil is rated ISO VG 100 .

The SAE 70W-90 SynLube Lube4Life Gear Oil is rated ISO VG 120 .

Saybolt Universal Seconds (SUS)

S aybolt Universal S econds is a measure of lubricating oil viscosity in the oil industry.

The measuring apparatus is filled with specific quantity of oil or other fluid and its flow timethrough standatized offrice is measured in Seconds.

Fast flowing fluids (low viscosity) will have low value; Slow flowing fluids (high viscosity) willhave high value.

Saybolt Furol viscosity

The efflux time in seconds required for 60 milliliters of a petroleum product to flow throughthe calibrated orifice of a Saybolt Furol viscometer , under carefully controlled temperature,as prescribed by test method ASTM D 88.The method differs from Saybolt Universal viscosity only in that the viscometer has a largerorifice to facilitate testing of very viscous oils, such as fuel oil (the word "Furol" is acontraction of "fuel and road oils").

The Saybolt Furol method has largely been supplanted by the kinematic viscosity method.

Engler degree

A measure of viscosity. The ratio of the time of flow of 200 ml of the liquid tested, throughthe viscometer devised by Engler, to the time required for the flow of the same volume of water gives the number of degrees Engler .

Redwood viscosity

method for determining the viscosity of petroleum products; it is widely used in Europe, buthas limited use in the U.S.The method is similar to Saybolt Universal viscosity ; viscosity values are reported as

"Redwood seconds."

Viscosity Comparison Table

Due to the fact that there are number of differing Viscosity measuring standards it issometimes confusing to determine what is the viscosity of fluid in a viscosity system of


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interest if the viscosity is quoted in units used in another viscosity system.

The chart below gives approximate equivalence of values for a typical conventional fluids.

Newtonian vs. Non-Newtonian Fluids

A Newtonian fluid can be described as a fluid that maintains constant viscosity across allshear rates (shear stress varies linearly with shear rate).

These fluids are called Newtonian because they follow the original formula established by Sir Isaac Newton in his Law of Fluid Mechanics.

Some fluids, however, don't behave this way.

In general, they are called non-Newtonian fluids.A group of non-Newtonian fluids referred to as thixotropic are of particular interest in usedoil analysis because the viscosity of a thixotropic fluid decreases as the shear rate increases.The viscosity of a thixotropic fluid increases as shear rate decreases. With thixotropic fluids,set-time can increase apparent viscosity as in the case of grease.


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Newtonian Fluid

Fluid whose viscosity does not change with rate of flow.

Examples of Newtonian Fluids

Straight Mineral OilSingle Grade Motor OilHoneyWater

non-Newtonian Fluid

Fluid whose viscosity does change with rate of flow.

Examples of non-Newtonian Fluids

MayonnaiseKetchupGreaseSynLube Lube-4-Life Lubricants

Generally speaking, a fluid is non-Newtonian if it is comprised of one substance suspended(but not chemically dissolved) in a host fluid.

For this to happen, there are two basic categories, emulsions and colloidal suspensions.

An emulsion is the stable physical coexistence of two immiscible fluids. Mayonnaise is acommon non-Newtonian fluid, comprised of eggs emulsified into oil, the host fluid. Becausemayonnaise is non-Newtonian, its viscosity yields with applied force, making it easy tospread.

A colloidal suspension is comprised of solid particles stably suspended in a host fluid.

Many paints are colloidal suspension. If the paint was Newtonian it would either spread easilybut run if the viscosity is low, or spread with great difficulty and leave brush marks, but notrun if the viscosity is high. Because the paint is non-Newtonian, its viscosity yields under theforce of the brush, but returns when the brush is taken away. As a result, paint spreads withrelative ease, but doesn't leave brush marks and doesn't run.

SynLube Lube-4-Life Lubricants are non-Newtonian, as a result they flow easily (as lowviscosity oil would) but create " thicker " oil film and " stick " to parts (as high viscosity oilwould).

Viscosity of non-Newtonian Fluids

If one were to measure the absolute viscosity of one of these commonly encounteredemulsions or colloids described above with a variable shear rate absolute viscometer (forexample, ASTM D4741), the measurement would decrease as the shear rate increases, up toa point of stabilization.

If one were to divide this stabilized absolute viscosity by the specific gravity of the fluid toestimate the kinematic viscosity, the calculated value would differ from the measuredkinematic viscosity.

This is because the equations in apply to Newtonian fluids only, not non-Newtonian fluidsdescribed above, which is why this discrepancy in viscosity measurement occurs.

Specific Gravity Effects


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The absolute and kinematic viscosities of a Newtonian fluid are related as a function of thefluid's specific gravity.

Kinematic Viscosity Measurement

Consider the apparatus in Figure above, the bulb that contains the sample oil, which isreleased when the vacuum is eliminated, then produces a head of pressure that drives theoil through the capillary tube. Can one assume that all fluids will produce the same head of pressure? No, the pressure is a function of the fluid's specific gravity, or weight relative tothe weight of an identical volume of water.

Most hydrocarbon-based lubricating oils typically have a specific gravity of 0.85 to 0.90.

However, this can change over time as the oil degrades or becomes contaminated (glycol,water and wear metals for example), which produces a differential between absolute andkinematic viscosity measurements.

In the interest of economy, simplicity and the fact that new lubricant test procedures arecommonly borrowed for used oil analysis, the kinematic viscosity of the oil is typically themeasured parameter used for trending and making lube management decisions.

However, in certain cases this may be introducing needless errors in determining theviscosity of an oil.

The problem can be reduced to simple mathematics.

As the viscosity equations suggest, the absolute and kinematic viscosity are related as afunction of the oil's specific gravity.

If both the viscosity and specific gravity are dynamic, but only one is measured, an error willoccur, and the kinematic viscosity will not provide an accurate assessment of the change inthe fluid's absolute viscosity, the parameter of interest. The amount of error is a function of the amount of change in the unmeasured parameter, the specific gravity.

Temperature Effects

The absolute and kinematic viscosities of a Newtonian fluid are related as a function of thefluid's specific gravity.

As fluids are heated up they expand, and thus their specific gravity is reduced, this in turnof course affects the viscosity.


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SynLube Lube4Life Synthetic Motor Oil is rated SAE 5W-50 (ISO 100)

Below is the list of SAE Viscosity Ratings in order of preference from Best to Worst:

The Best PossibleSAE 0W-60 (Very Expensive)

1.

The Best AvailableSAE 5W-50 (Possible only with Fully Synthetic Motor Oil)

2.

Very GoodSAE 5W-40 - for Colder Climates (Synthetic or Blend)

SAE 10W-50 for Warmer Climates (Synthetic or Blend)

3.

GoodSAE 5W-30 for Colder ClimatesSAE 10W-40 for Normal ClimatesSAE 20W-50 for Hot Climates**

4.

AverageSAE 10W-30 for Light Duty UseSAE 15W-40 for Heavy Duty Diesel Applications

5.

AcceptableSAE 30 for Normal Climates, but not in WinterSAE 40 for Warmer Climates, but not in WinterSAE 50 for Hot Climates, but not in WinterSAE 5W-20 for sub-zero temperatures, Winter use only (unless use is prohibited by the enginemanufacturer)

6.

To make sense of the above recommendations we must define what all those climaticconditions mean. The definitions can be found in the table below:

ClimaticCondition

ClimaticCode

MinimumLow F

MinimumLow C

MaximumHigh F

MaximumHigh C

TypicalCoolantTemp.F

TypicalCoolantTemp.C

Ideal SAEViscosity

Very Hot AA >80 >26 >110 >43 212 100 60

Hot A >60 >16 >110 >43 200 93 50

Warm B >50 >10 4 -7


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Recognize that non-Newtonian fluids don't provide the same film protection for a givenkinematic viscosity as a Newtonian fluid of the same kinematic viscosity. Because theviscosity of a non-Newtonian fluid will vary with the shear rate, the film's strength isweakened under operating load and speed. That is one of the reasons that emulsified waterincreases the rate of wear in components such as rolling element bearings, where fluid filmstrength is critical (of course, water also causes other wear mechanisms like vaporouscavitation, rust and hydrogen embrittlement and blistering).

Viscosity is a critical fluid property, and viscosity monitoring is essential to oil analysis.Absolute and kinematic viscosity measurement techniques can produce very different results

when testing used oils. Be sure the ins and outs of viscosity measurement and viscous fluidbehavior are understood so accurate lubrication decisions can be made.

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