Practical Lubrication & Filtration

[Doctor Lubricity]

Motor Oil

 

Before one can discuss the difference between a Semisynthetic, Full Synthetic and 100% Synthetics we need to know the blend stock that make these categories what they are.

What you normally get in such a presentation are the API Group boundary specifications (You can Google those if interested) but this time we will look at the typical values for those Groups and some subsets as it will paint a much truer picture.

 

Group 1:

 

Mineral oil, solvent refined.

65 – 85% saturates, 15 – 35% aromatics

Sulfur 300 – 3000 ppm

VI 95 to 105.

Possible viscosity range @ 212F = 4 – 32 cSt

 

Group 2:

 

Mineral oil, hydrocracked

93 – 99% saturates, 1 – 7% aromatics

Sulfur 5 – 300 ppm

VI 95 – 118.

Possible viscosity range @ 212F = 4 – 30 cSt

 

Group 2 Plus:

 

Mineral oil. A more refined Group 2. Not technically a group but a type of Group 2.

Saturates and Aromatic contents better than Group 2

Sulfur lower end of Group 2

VI 100 – 120.

 

Group 3:

 

Mineral oil, dewaxed, hydrocracked and hydro-treated and partially isomerized.

 

95 – 99% saturates, 1 – 5% aromatics

Sulfur 0 – 30 ppm

VI 123 - 150.

Possible viscosity range @ 212F = 4 – 8 cSt.

 

GTL: (a subset of Group 3)

 

Mineral oil synthesized from Natural Gas

Trace unsaturated.  

VI greater than 135.

Sulfur less than .0002% or 0 - 2 ppm

Cliff Notes version of GTL. Is natural gas that is converted to an ultra-sweet mineral crude that covers the range between light naphtha and lube oil. Highest percentage of isoparaffins. The most refined and cleanest of the mineral oil class but a mineral oil none the less. Once the synthetic crude in made it is processed like any other crude oil.

 

So ends the mineral oil Groups.

 

So what is the result of all this processing? As the process advances from Group 1 through Group 3 that C15 – C50 feed stock that came from the Atmospheric column or was synthesized becomes cleaner and more isoparaffinic.

What does that do?

1.)        Increases resistance to thermal and free radical oxidation.

2.)        Lower cloud point 

3.)        Results in an increase of the VI.

4.)        Possible viscosity range narrows

Are there down sides? Sure, but blenders know what these are and compensate for the minuses during formulation.

Moving on to the non-mineral products:

 

Group 4: (aka PAO)

 

Synthetic Polymer from natural gas and ethane conversion. Ethylene, C10 and C12 homo-polymers are intermediates not end products.

Greater than 99% saturates, aromatic in the ppb range. Nil.

Sulfur 0 ppm

VI 125 – 150.

Possible viscosity range @ 212F = 4 – 70 cSt

Unlike mineral oils the carbon chain length is singular and as such has a boiling point that varies with viscosity instead of a boiling range like mineral oil. It can have natural unassisted pour point of – 49F.

 

Group 5:

 

Everything else; POE’s Diesters. (Includes materials not routinely used in motor oil)

These are high VI synthetic single chain engineered ester polymers manufactured from plants oils/fats.

If you need the whole nine yards pick up a copy of “Synthetics, Mineral Oils and Bio-based lubricants” by Leslie R Rudnick

The materials in this book will explain the synergies that produce various beneficial results and the whys at the molecular level.  

As they are not mineral oils they haven’t any API touchstone requirements. They are never used alone. The finished product specs depend on the blender’s intentions and goals. Discussion of any API Group’s shortcomings as an individual component are therefore superfluous. Discussions of their strengths however are enlightening.  

 

 

Edited April 18, 2020 by Doctor Lubricity

[Doctor Lubricity]

Motor Oil 2

 

What’s in the bottle?

 

Re-refined/Recycled:

 

Literally anything within the carbon chain fence. C18 – C34. This is a cleaned up waste/recycled/spent oil stream. It may or may not contain some virgin materials. Example of a virgin/re-refined blend is Valvoline NextGen series of motor oils.

 

Conventional:

 

Groups 1 or 2 or 2 Plus or any combination of these three. In this day and age Group 1 oils are rarely in any named motor oil. The majority of the Group 1 materials are used in industrial lubrication in applications were oil temperatures rarely exceed 160 F.

 

Semi-Synthetic:

 

A blend of Conventional and a Group III. This can include GTL oils. Problem is that there isn’t any legal minimum requirement so the synthetic portion literally could be under 5% without reprisal.

 

Full Synthetic:

 

Must contain some Group 3. Could be all within this group. But may also contain some fraction of a higher group oil as well. PAO is often the go to here. GTL’s and conventional Group 3 blends are gaining traction.

 

100% Synthetic:

 

PAO (Group 4) and/or any material from Group 5.

 

Commentary:

 

These are listed above from lowest to highest performance. The lower in this group you go the more of the can becomes additives and their carriers.

 

All common additive carrier oils are conventional mineral oil and may be as little as 5% to as high as 25% of the can. This literally means there is no such thing as a truly 100% Synthetic oil. It is a marketing term used to distinguish the differences between Full and 100% for labeling purposes. Between a PAO/Group 3 and a PAO/Ester.

Edited April 18, 2020 by Doctor Lubricity

[Doctor Lubricity]

Motor Oil 3

 

Aniline points are indicators of polarity. They indicate solvency, lubricity and film strength. It is the temperate at which aniline and the test base mixed in equal parts separate. No longer miscible.

Aniline points rise with 40 C viscosity.

 

(Source: NIAZ SALIH M.)

Values based on viscosities within the motor oil ranges.

Aromatic oil, 75% aromatic, 32.2° - 48.9°C (90 – 120 F)

Naphthenic oil, 40% aromatic, 65.6° - 76.7°C (150 – 170 F)

Paraffinic oil, 15% aromatic, 93.3° - 126.7°C (200 – 260 F)

 

(Source Shell Oil & Chevron Research)

Values below based on a viscosity of 2 cSt.  

Group 1 = 75 C / 167 F (Naphthenic)

Group 2 = 90 C / 194 F (Paraffinic) 

Group 3 = 102 C / 216 F (Paraffinic)

Group 3 = 114 C / 237 F (GTL 100% Isoparaffins)

Group 4 = 105 C / 221 F (PAO)

Group 5 = 20 C / 68 F (Polyol Ester at 5 cSt)

Group 5 = 30 C / 86 F (oil soluble PAG)

 

High aniline points in a mineral oil say a base oil has:

1.)        Lower solvency  

2.)        Lower lubricity

3.)        Higher film strength

Low aniline points in a mineral oil say a base oil has:

1.)        Higher solvency

2.)        Higher lubricity

3.)        Lower film strength

4.)       

 

Caution: The use of the terms Higher and Lower are relative not absolute. The do not indicate by what degree of measurement and are only a directional indicator. More or less.

It is the blender’s job to create a lubricant that will hold the intended additive package (enough solvency) with enough cushion to prevent drop out and maintain sufficient film strength at the lowest friction (lubricity).

 

Example: (Source Exxon/Mobil)

 

A 20% POE 80% PAO blend produces a sliding friction coefficient of 0.1 in the 2 to 4 cSt range.

In comparison the same 2 -4 PAO alone has a sliding coefficient 200 – 230% higher. ASTM D6079 HFFR.

 

Synergies make good lube oils. Every base has some strengths and some weaknesses. Arguing them is pointless. Discussing them is the fruitful act of acquiring knowledge. Knowledge leads to better decisions. Knowledge is only useful if it is accurate.  

 

Quoting from Lube Magazine 89 Feb 2009:

 

Talking about lubricity, one refers to the slipperiness of lubricant films separating the rubbing surfaces from each other. As long as the lubricant film is thick and resilient enough to prevent direct asperity-asperity contact, the coefficient of friction tends to be very low. In this case, one talks about the film lubrication regime. However, solvent power alone does not guarantee good lubricity. Lubricity requires that polar and non-polar molecules be present simultaneously. Since metal surfaces are highly polar, polar oil molecules dissolved in nonpolar ambient tend to adsorb to the metal surface, forming a protective surface film. Strength of the film and solvent power are linked to the same cohesion parameters.

 

[End quote]

 

It is the synergy between the PAO and POE that makes this blend shine. In boundary conditions the POE attaches itself to the metal and the PAO molecules become the cream in the Oreo. It is the PAO moving over the POE that creates the exceptional slipperiness (lubricity) and excellent film strength.

To duplicate as closely as possible, this ability in a non-polar higher mineral oil group (Group 3) EP additives are required plus friction modifiers.

In all practical terms it is synergies that let us have our cake and eat it too

Edited April 18, 2020 by Doctor Lubricity

[Doctor Lubricity]

Motor Oil 4

 

Is a sharp knife “better”?

 

Better than what? A Colt 45? A sharp stick? A dull knife? A water balloon? ‘Better’ needs a standard to be judged against. So let’s talk about a standard.

 

I have a broad axe, a chain saw, a Samurai sword and a cleaver and I have hog carcass’s hanging in a cooler so I rate these tools by their ability to cleanly cleave that little pig in two with the least effort. After a result is achieved I wish to butter some bread. Do I use that information to choose the ‘best’ tool from this list to cut and spread a pat of butter? No!

 

The test not only needs a standard but one that is suitable for the task we wish to apply it against and therein is the rub with motor oil testing. Many test are designed to find the failure point. To take the oil to a place that it will never see in day to day operation.

 

Shell four ball scar test a case in point. Along with all its iterations.

 

Let’s example a range of lubricants that test film strengths whose results lie between 90,000 psi and 135,000 psi. We can make all manner of claims about protection. That is as long as we don’t reveal that real world loads never exceed 80,000 psi. (Not real values just numbers posing a real fact).

 

How about additive levels? Are we not conditioned to believe “More is better” or “If a little is good an excess falls just short”?

 

Phosphorus levels for (ZDDP) are tested using ASTM D-4951 or D-5185. According to the API Service Categories the levels are:

 

SH 1200 ppm maximum

SJ 1000 ppm maximum

SL 1000 ppm maximum

SM 800 ppm maximum 600 ppm minimum (D-4951 method only).

SN 800 ppm maximum 600 ppm minimum (D-4951 method only).

Initially ZDDP was used only as a corrosion inhibitor. It was found later to have pretty good antiwear properties. The part that gets all the attention.

 

ZDDP is also a major contributor to the antioxidant package.

 

Leave a peeled apple on the counter and it turns brown. That is oxidation.

 

Oxidation in oil is a precursor to varnish and sludge. Insolubles.

While an apple will do this at room temperature fluids used as lubricant need some heat to get them initiated. Some fluids resist this breakdown mode better than others. The worst among them is a Group I mineral oil having an initiation temperature of 160 F and the best of the bunch, POE which requires 250 F to get going. Increasing the temperature 10 C or 18 F doubles the rate of oxidation. The next step doubling the last. It gets ugly quickly.

 

Thermal breakdown is NOT the same thing as oxidation and requires higher temperatures. Some mineral oils as low as 250 F and POE’s about 300 F. Antioxidants will not prevent thermal destruction but can delay oxidation onset. The byproducts of thermal breakdown are also insoluble materials. This type of heat destroys seals and promotes oxidation precursors to become varnish and sludge.

 

Lubricating fluids are also subject to other things that degrade their usefulness. Nitration, contamination and volatility to name a few. Additives are used to combat and contain/control and they all require additives.

 

Lubricating fluids (oil) are a chemistry. A chemistry that when whole reduce wear; clean and cool and if really good lowers friction and parasitic energy losses. When that chemistry is altered by any means it loses its effectiveness in doing its primary functions. Alteration comes by oxidation, thermal break down, nitration, acidification, particulate abrasion, dilution, emulsification, foaming, misting; lose enough properties and the motor fails. It can be sudden, it can take hundreds of thousands of miles.

.

 

Wear is a thing that is controlled, not eliminated.

Edited April 18, 2020 by Doctor Lubricity

[Doctor Lubricity]

Motor Oil

Filtration 1

Does it matter how good the oil is if it is full of abrasive solids?

 

Picture two glass surfaces separated by a layer of the best oil on earth one thousandth of an inch apart. One is stationary and the other in motion. Now picture a rough diamond one thousandth of an inch in diameter entering that space. Can you picture the scratch? Now picture thousands of particles that size and that hard wearing away at those surfaces. This is three body wear and it’s what happens to your motor when a particle harder than the materials of construction enters the lubrication system that is the same size as the oils film thickness.

 

Note that this problem is a function of the size of the particles, the number of particles and the relative hardness of each entity.

 

There are isles of research at major universities dedicated to the study of wear and dirt. Some highlights.

 

Debris in motor has a limited number of routes into a healthy well maintained motor.

 

1.)        Ingestion.

2.)        Poor oil change hygiene.

3.)        Wear metals.

4.)        Byproducts of oil oxidation/degradation/Soot.

5.)        Ambient levels in fresh oil.

 

Ingestion is via the motors air inlet. Some interesting facts. 80% of all airborne contaminates are under 10 micron. Some of it is biological and quite soft. Of the 20% that remains most of that is silica. Hard as metal working tools. According to Exxon/Mobil good air filters trap nearly all particles to 5.5 micron. Oil film on a cylinder wall has a film thickness between 0.3 and 7 micron and while the ring face may be quite hard the cylinder wall is not. PCV fresh air comes from the downstream side of the air inlet in most modern motors.

 

Poor oil change hygiene. That dirty funnel. Dirt around the oil inlet. There is no limit to amount or size.  

 

Wear Metals. Interesting note is that ‘normal’ wear metals rarely exceed 10 micron in size. This is also about the limit of detection by elemental oil analysis. To detect the presence of larger particles a PQ index can be run. IF that number is smaller than the iron ppm value then there are no 10 micron or larger particles present. IF it is larger a third test can be run to quantify. Ask your lab. “Normal” wear and its rate is monitored by the elemental variations in particle quantity. Rapid changes in PPM under 10 micron are flagged.

 

Byproducts of Oil Oxidation/Degradation/Soot. Unless the additive package is depleted leading to amalgamation, the detergent/dispersant package of a modern motor oil will hold these particles to 0.5 to 1 micron. Until they amalgamate they are spherical. They are also relatively soft.

 

Conclusion: To this point the largest particles that enter your motor under normal conditions, or are created as part of normal wear is 10 micron and those particles are measured in the ppm range.

 

Ambient levels in fresh oil. Oils beginnings are in the dirt. How much of it remains is up to the processor. How clean it is in the bottle depends on how well it was processed and filtered. Particle size can reach 70 -100 micron in a bottle of new oil. Large enough to be seen by the naked eye or it can be exceeding clean. Clean enough that the best spin on filter has little to do. 

 

Conclusion: During normal operation particles exceeding 10 micron are nearly nonexistent. Over 10 micron they are the result of oil choice and abuse and maintenance hygiene.

 

During abnormal operation fatigue failures, spalling primary, sloppy maintenance and additive package depletion are primary sources of larger particles.

 

In the next post we will look at the methods used to quantify size and count and what those counts mean. How to read the report. It isn’t that hard..

Edited April 18, 2020 by Doctor Lubricity

[Doctor Lubricity]

Motor Oil

 

Filtration 2

 

Dirt/wear and contamination particles come in all sizes and as indicated in the last post how they affect wear depends on quantity, size and hardness. Tribology is the study of wear.

 

During that study devices were developed to gauge size and count then number of particles in an oil sample. Several in fact. One of the most popular is a test named APC or Automatic Particle Counting and the test method is ISO-11500. The reporting method is ISO-4406. An instrument takes a metered amount of your oil and counts the number of particles in the sizes of 4, 6, 10, 14, 21, 38, 70, & 100 micron. The raw data will be given for some to all of these sizes depending on the lab but the ISO-4406 sample will be given in either a two or three number code. It might look like 22/20/19 or it may look like 20/19 displaying just the last two numbers. In the three number code these numbers represent the counts of 4, 6 and 14 micron particles while the two number report gives just the 6 and 14 micron values. The numbers are not a count actually but a code that represents a ‘range’ of counts and the table looks like this:

 

Reference materials from:

 

WWW.Control and Instrumanetation.Com

 

 

 

 

So in our 22/20/19 example above this means in this sample there were:

More than 20,000 and up to 40,000 particles of 4 micron in size

More than 5,000 and up to 10,000 particles of 6 micron in size

More than 2,500 and up to 5,000 particles of 14 micron in size

 

Note that each number for this reporting method DOUBLES the number of particles of that size! A small change is a big deal.

 

So what does that indicate? CC Jensen, a Danish oil testing Concern gives us the following guidelines:

 

ISO 14/12/10 Very Clean Oil

ISO 16/14/11 Clean Oil

ISO 17/15/12 Lightly Contaminated

ISO 19/17/14 New Oil

ISO 22/20/17 Very Contaminated and not suitable for any service.

 

In addition CC Jensen gives a table showing how engine life is increased by cleaning up the oil. For example cleaning the oil from 19/17/14 to 13/11/8 will extend motor life by a factor of 6X.

 

But even cleaning it two “Life Extension Classes” will double motor life. So perhaps giving those classes would be useful:

 

21/19/16

20/18/15

19/17/14

18/16/13

17/15/12

16/14/11

15/13/10

14/12/9

13/11/8

 

Note: On average NEW OIL is two classes into contaminated.

 

In the next post we will look at how particle size and hardness affects wear.

.

Edited April 18, 2020 by Doctor Lubricity

[Doctor Lubricity]

Motor Oil

Filtration 3

 

Source of graph: Machinery Lubrication

 

 

There is a GM study that is referenced from time to time that is said to have indicated that particles of 5 micron do the most damage. Look at this Relative Engine Life Graph and ask yourself a question. Do you use 80 grit to remove paint or polish it? Do you use 5,000 grit to remove paint or polish it?

 

Size does matter and it matters allot but so does the volume of each particle, the count. Dirt in oil is a Maxwell

Boltzmann Distribution. Specifically the blue line.

 

Source (Wiki)

 

 

 

The opening graph shown is referenced to a Beta Ratio = 75.

 

It’s speaking about an oil filters efficiency in removing particles of a specific size so let’s decipher this ratio.

 

A Beta Test feeds a filter one million particles in a closed loop and after the number of passes specified by the test counts the umber of particles remaining on the downstream side of the filter. If we divide one million by the Beta Ratio we know how many particles remained. Let’s do that; 1,000,000 / 75 = 13,333 are left.

 

Now we subtract 13,333 from 1,000,000 = 986,667 and divide that by 1,000,000 and multiply by 100 to get a filtering efficiency of 98.7%.

 

So the opening graph says engine life increases when we filter our oil to a point where we are removing 98.7% of the particles of a given size represented in the graph. Let’s work the graph as it is shown.

 

The engine life factor for filtration at 98.7% of 40 micron particles is 3. Find 40 micron on the horizontal line and go up the curve then left to the vertical line to 3. Okay that is your reference point.

 

You choose a filter that has a Beta Ratio of 75 at 10 micron and repeat. That factor is 8.

 

Divide 8 / 3 = 2.67X which means if you were getting 150,000 miles between rebuilds with a 40 micron filter you will get 400,500 miles between rebuilds filtering with a Beta = 75 @10 micron filter.

 

I said we would cover hardness as well in this issue. In the last post we noted that for a particle to cause damage in the three body wear model it has to be harder than the surfaces it is contacting. It was also noted that the MAJORITY of particles in a well maintained motor are quite soft and do no damage unless they are allowed to amalgamate and plug oil passages.

 

Example the lifter roller to cam lobe space is exceedingly small. Just a few micron but it is also exceedingly hard. Most particles that enter this space are fractured into smaller pieces. Some could be hard enough to cause micro fractures in those surfaces and initiate spalling. That would lead to a catastrophic failure.

 

Journal bearings are quite soft but the space in a running motor are quite large. 25 micron is equal to 1 thousands of an inch. Particles larger than the space can’t enter and those smaller pass through harmlessly.

 

Ring face to bore. This is the place some damage can be done. This clearance ranges from 0.3 micron to 7 micron in a running motor depending on the point of crank rotation. While the rings are quite hard, the bores are less so. This is the space the GM study was talking about, bore wear.

 

Let’s tie these thoughts together. Filters don’t cut off the head of the snake and leave the body whole. In our example of comparing a 40 micron to a 10 micron filter it is good to be aware that the 10 micron just doesn’t do a better job a 10 micron but a better job at filtering every size below as well. So the graph isn’t just showing what happens at the peak size but at every size below. 

 

Next time we look at the filters themselves.  

Edited April 28, 2020 by Doctor Lubricity

[Doctor Lubricity]

 Motor Oil

Filtration 4

 

This is a discussion, not a recommendation nor endorsement of any filter. 

 

Filter efficiency is easier to get if you are looking for it correctly. The box isn’t that. You are looking for ISO 4548-12 results. Thing is these test results can have any point of reference that marketing wishes and they wish to look stellar. Usually reference, however is 20 micron. So let’s start with an easy one to get.

 

Royal Purple is not bashful about publishing ISO 4548-12 results.

 

25 Micron 99.0% Beta 100

20 Micron 98.7 % Beta 76.9

10 Micron 80.0% Beta 5

 

Let’s look at some others I plucked form a quick Google search:

 

WIX / NAPA Gold: 20 micron, 95%, Beta Ratio 20

Mobil 1: 30 micron, 99.9%, Beta Ratio 1,000 (red flag)

AC Delco Professional: 20 micron, 95.4%, Beta 21.7

AMSOIL Ea17: 20 micron, 98.7, Beta 75 

 

Beta of 75. So in descending order for the filters fitting the GM Ecotec3:

 

Purolator Pure One PL22500 > 12 micron

Royal Purple @ 18/19 micron

AMSOIL Ea017 20 micron.

WIX/NAPA @ 22 micron

AC Delco PF63E @ 23/24 micron.

Mobil 1 M1-212A @ 25 micron

 

Mobil 1 reports a high filter percentage by raising the micron passing reference point.

 

Sometimes the  ‘Extended Mileage’ filters gain the mileage extension by lowering the filter efficiency. 

 

Filters that refuse to supply ISO 4548-12 results with a point of reference should be avoided. Look hard. Sometimes there is a small asterisk at the percentage whose point of reference is in exceedingly small print somewhere else on the wrapper or web page. This is just a sampling.

 

I’m not going to get into construction. This is about efficiency.

 

Using the relative wear chart from the preceding post we have a range of filters in this small sampling with relative engine life factors ranging the 4 to 12 values meaning from top to bottom:

 

There is a 3X service life to be gained by an informed choice.

 

Next post will be on the ambient contamination in ‘new oil’. 

 

You will learn that you don't have to pay for an expensive ISO 4548-12 test but rather can infer it from some really simple test additions to your normal UOA. Have a favorite? Compare to the started list.

 

 

Edited January 7, 2021 by txab

[Doctor Lubricity]

Motor Oil

Filtration 5

ISO 4406 Classes:

Virgin oils compared to industry standard cleanliness.

 

 

 

Besides the obvious wide array of manufacture regard for what is clean a stunning stand out here is the effect a good filter can have on the oil in just a few hundred miles.

 

The actual particle counts for the sample filtered with an AMSOIL Ea were:

 

4um = 128

6um = 70

14um = 12

25um = 2

 

This would seem to validate Ea filters are 20 micron referenced.

 

Learn to rely on the ISO-4406 result to tell you how your filter is doing and not the packaging.

It’s been mentioned several times that a motor does not normally make particles larger than 10 micron. NORMALLY. But they can be introduced as you can see when you pour a bottle of your favorite oil into your motor.

 

Actual particle counts for virgin Mobil 1 5W30 pre-filtration :

 

4um = 21,400

6um = 8,450

10 um = 1558

14 um = 173

18 um = 68

21um = 47

38 um = 10

50um = 7

 

Particles of this size would remain in your motor filtered by your local box store $2 filter. Those are 40 micron typically.

 

When you use a good filter on dirty oil you can certainly clean it up but it does put a large initial load on the filter for a few hundred miles.

 

Dirty oil and a poor filter is more common that one might think.

 

 

 

Edited May 14, 2020 by Doctor Lubricity

[Doctor Lubricity]

Reserved

[Doctor Lubricity]

Motor Oil 4

Viscosity Index Calculation

 

Viscosity is defined as:  A measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. (Wiki).

 

We are all aware that viscosity is temperature dependent. For this reason we need a reference point to compare one fluid to another. Depending on what aspect of the fluids viscosity we are concerned with we may need several.

 

In the early 20^th century it was noted that oil from Pennsylvania changed less with temperature than oil from the Gulf region. Two temperatures were selected as stable reference points; 40 C and 100 C (104 F and 212 F).

 

It was further noted that by controlling elements of distillation that a lubricating oils viscosity at the 100 C point could be manipulated so that any viscosity requirement between 4 and 32 cSt was possible and that oils viscosity at 40 C was not directly linked to its 100 C viscosity.

 

A W30 has a 100 C viscosity median of around 10.5 cSt but a straight 30 from made from Penn crude would have a 40 C viscosity of 88.95 cSt while one made from a Gulf crude would display a 40 C viscosity of 160.6 cSt. (End Note 1)

 

Because of copyright laws I cannot publish the ASTM table these figures were taken from but I can tell you that you can obtain them from ASTM Document D 2270-04 with a bit of searching.

  

The oil we wish to index which shares the same 10.5 cSt 100 C value has a 40 C value of 120.0 cSt. The math then goes:

 

VI = ((A-B) / (A-C)) * 100

VI = ((160.6 - 120) / (160.6 – 88.95) * 100

VI = 56.7

 

As you can see from reading oils data sheets the VI can and is normally today well over 150. The math is a bit more complicated and the intent here is not to teach anyone to calculate VI but to understand what that number is and what it means.

 

Most simply it is an oils 40C viscosity proportionality ratio to two know reference oils ratio of which all three share the exact same 100 C viscosity. The number is only an indicator and not an absolute value.  The higher the VI the less change in viscosity there is between the 40 and 100 C references. In an ideal world the VI would be infinite and the 40 and 100 C viscosities would be identical.

 

So how is it we have base and finished oils with VI’s over 100?

1.)        The removal of wax. Saturation of hydrocarbons. Carbon chain fractionation. Changes in base  oil chemistry not found in normal distributions in any ground crude.

2.)        New base oil types not derived from mineral crudes.

3.)        High molecular weight viscosity index improvers or more simply, additive chemistry.

 

Something missed by even astute consumers is the fact that several base oils, such as Esters, PAG and PAO do naturally what chemistry does for mineral oils. Group III mineral oils are a step in between.

 

In the very first post on motor oil in this thread in discussion of base oils you will find the attending VI data possible for each type. In review you will note that processing a mineral crude can only take you so far.

 

It is now possible to manufacture a 10w30 with the 40C viscosity of a straight 15W and the HTHS viscosity of a straight 60W and the cold temperature pumping viscosity of a 0W.   

Edited January 7, 2021 by Doctor Lubricity

[Doctor Lubricity]

Oil Change Intervals 

Color method

 

The lubricant in you automatic transmission will stay in pretty good shape for 50,000 miles. Aviation gas turbine oils last longer, maybe 5 to 15 years. Stationary steam turbines may go 20 to 30 years! Yet in a gas motor 2,500 -7,500 miles. 

 

So what is the difference that creates such a wide range of usefulness between these applications for the same base oil selection? 

 

(Photo by AMSOIL)

 

Several things but the biggest is combustion gas degradation. Turbines, even ones run at high oil temperatures do not see combustion gasses. Neither do ATF's. 

 

Depending on base oil and additive package different 'brands' of motor oil will darken, degrade, at different rates given the EXACT same use. There is no 'standard' oil change interval. There is an interval for your motor and your service and your choice of oil and filter. 

 

The same oil in the same service, in the same motor will darken at different rates as blow by increases due to wear and or damage caused by time or abuse. A good ring seal is a really big deal; losing it over the useful life of the motor should shorten the OCI.  Getting a good ring seal past assembly a function of the break-in. If your observant you would have noticed that the first few oil changes of a new truck get darker quicker. 

 

Heat cycling will degrade, darken the oil. The fewer heat/cool cycles the oil experiences over the same number of miles the longer it will take to darken, degrade the oil. A city dweller with a 5 mile commute will need to change oil more often than the professional driver that doesn't shut off for days. 

 

Excessive heat will darken it quickly. A stuck thermostat, blocked radiator or other external coolant failure or an exceedingly heavy load over a long enough period of time can kill the oil in one occurrence. 

 

Fuel. Diesel is dirtier than gasoline and it dirtier than alcohol.

 

In a nutshell dark oil is telling you it is degraded. It doesn't tell you the reason, just that it is. Combustion acid promoted oxidation,  overheated or cyclic heating, soot, additive depletion. But oxidized oil no longer has the same chemical structure it had new and can not perform as it did new.

 

When the oil turns black sludge is on it's heals. Oxidation can not be effectively filtered out in the motor. Exchange for new.

 

Yes, oil can be dark due to the additives and sometimes dyes and if that is the case for your choice this method is impractical. But when it can be used; one might ask if it can still be functional for some longer period of time. Maybe, but it would take UOA's to determine that. This isn't a thing that can be done by eyeball once it has gone past dark brown.