Thin vs Thick Discussion, Chapter 3

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Motor Oil 103
Part Three. You have a synthetic mind.

Let us compare mineral and synthetic oils. I will not talk about chemical but rather functional differences. We discussed before how some mineral oils are too thick at startup yet too thin when hot. The viscosity was corrected with the hot engine by adding VII, viscosity index improvers, VI improvers.

A 10W-30 multi-grade mineral based oil is made from a 10 grade oil and has VI improvers added to thicken the product in a 212 F engine. It acts as a 30 grade oil when hot. It acts more as a 10 grade oil at startup. I remind you that a 10 or 5 or 2 grade oil is still too thick to provide optimal lubrication at startup. They are all too thick at startup. There is currently no general engine oil thin enough to operate correctly at startup. They all cause excessive wear at startup. Again, we are discussing the needs of my single hypothetical engine for around town driving.

Oil type.. Thickness at 75 F ..Thickness at 212 F (For mineral based oils)

Straight 30..........250....................10
10W-30...............100....................10
0W-30.................40.....................10

Straight 10..........30.....................6
Straight 5...........20.....................4
Straight 2...........15.....................3
Straight 0...........12.....................3 est.

Remember that a Straight grade oil is also and more correctly a Single grade oil and not a Multi-grade oil. A grade is a group of oil properties. The actual viscosity varies widely with the temperature.

Let’s look at the make up of synthetic based oils. A 10W-30 synthetic oil is based on a 30 grade oil. This is unlike the counterpart mineral oil, based on a 10 grade product. There is no VI improver needed in the synthetic 10W-30 oil. The oil is already correct for the normal operating temperature of 212 F. It has a thickness of 10 while you drive to work. It will never thin (by VII depletion) yet has the same long term problem as the mineral based oil. They both thicken with extended usage/age.

Full synthetic oils are derived in the laboratory. They are pure, usually nearly clear. I describe mineral based motor oils as a distilled, concentrated product. The impurities need to be removed from the raw petroleum. These oils are therefore less clean and contain many impurities. Again, the problem is really more of theory than practice but the difference does exist.

As an aside, one of the most costly additives (per cc) that goes into motor oils are the dyes or coloring agents!

People repeatedly say that synthetic oils are more stable in a hot engine. I hear that they lubricate better. The answer is yes and no. Oil molecules do not break down, just the additives. Generally, the synthetic oils do not have VI improvers so have less to lose.

There are some properties of synthetic oils that actually may result in a little less wear than with mineral oils. These help increase your gas mileage as well. Due to a reduction of internal friction of the synthetic oil your engine will run a bit cooler. Wear increases as temperature increases, all other things being constant.

A main advantage that the synthetic has over the mineral based oil is the ability to lubricate better at startup. Both types of oil have the similar specifications at 104 F, 212 F and 302 F. It is often the startup viscosity characteristics that separate these oils. In general synthetic oils do not thicken as much on cooling. They have better fluidity as the temperature drops.

A synthetic oil that is labeled as 10W-30 is less honey like as a mineral based 10W-30 motor oil at startup. They both have a thickness of 10 at normal operating temperatures. At 75 F the synthetic is not as thick. At 32 F the difference between the two is even greater. At 0 F the mineral oil works poorly yet the synthetic works fairly well. Just keep the RPM to a minimum.

At temperatures below zero you may not be able to start your car with mineral oils while the synthetic oils may be used to -40 or - 50 F. Oils are so thick that the normal method of viscosity measurement is not possible. Instead we measure if the oil can even be pumped or poured. Again, we are only discussing a single category of oil, the multi-grade 10W-30 oil grade.

I took this excerpt from the web about Mobil 1 oils: They compared a 5W-30 synthetic Mobil 1 oil to a mineral based 10W-30 and a 10W-40 in ice cold conditions. The engine turned over at 152 RPM with the synthetic 5W-30 Mobil 1. The 10W-30 and 10W-40 mineral oils turned over at 45 and 32 RPM respectively. Neither of those engines started.

Motor oil becomes permanently thicker with exposure to northerly winter type weather. This is more of a problem to mineral based oils. Waxes form. This is why it is a bad idea to even store a bottle of oil in a cold garage. It goes bad on the garage shelf just because it is exposed to the cold.

To recap, synthetic oils have similar characteristics as mineral oils at operating temperatures. Often the synthetic oil will however be less honey - like at startup even though it has the same API / SAE rating. Yet the synthetic 10W-30 grade oil is based on a heavier 30 grade oil while the mineral based 10W-30 oil is based on a thinner 10 grade oil. They are both similar at operating temperatures yet the 30 grade based synthetic is actually less thick at startup and less honey - like at low temperatures. This is the opposite of what common sense dictates.

These days many mineral based oils are in fact mixed with some synthetic components. Some synthetics may not be purely synthetic. There may not be a big difference in motor oil quality between the major brands. There is evidence that for general use any main line oil will work well enough, mineral or synthetic.

As one can see this is no easy topic. Are you with me?

AEHaas
 
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737
Location
NC
Thank you for the thoughtful précis of this complex topic. I think your salient point is well stated; 'There is evidence that for general use any main line oil will work well enough, mineral or synthetic.' :geek:
 

MolaKule

Staff member
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A 10W-30 multi-grade mineral based oil is made from a 10 grade oil and has VI improvers added to thicken the product in a 212 F engine. It acts as a 30 grade oil when hot.

Not quite. Motor oils are made from binary and tertiary mixtures of disparate viscosities of various base oils. VII's are then added to achieve the target VI.
 
Messages
27,485
Location
PNW
Motor Oil 103
Part Three. You have a synthetic mind.

Let us compare mineral and synthetic oils. I will not talk about chemical but rather functional differences. We discussed before how some mineral oils are too thick at startup yet too thin when hot. The viscosity was corrected with the hot engine by adding VII, viscosity index improvers, VI improvers.

A 10W-30 multi-grade mineral based oil is made from a 10 grade oil and has VI improvers added to thicken the product in a 212 F engine. It acts as a 30 grade oil when hot. It acts more as a 10 grade oil at startup. I remind you that a 10 or 5 or 2 grade oil is still too thick to provide optimal lubrication at startup. They are all too thick at startup. There is currently no general engine oil thin enough to operate correctly at startup. They all cause excessive wear at startup. Again, we are discussing the needs of my single hypothetical engine for around town driving.

Oil type.. Thickness at 75 F ..Thickness at 212 F (For mineral based oils)

Straight 30..........250....................10
10W-30...............100....................10
0W-30.................40.....................10

Straight 10..........30.....................6
Straight 5...........20.....................4
Straight 2...........15.....................3
Straight 0...........12.....................3 est.

Remember that a Straight grade oil is also and more correctly a Single grade oil and not a Multi-grade oil. A grade is a group of oil properties. The actual viscosity varies widely with the temperature.

Let’s look at the make up of synthetic based oils. A 10W-30 synthetic oil is based on a 30 grade oil. This is unlike the counterpart mineral oil, based on a 10 grade product. There is no VI improver needed in the synthetic 10W-30 oil. The oil is already correct for the normal operating temperature of 212 F. It has a thickness of 10 while you drive to work. It will never thin (by VII depletion) yet has the same long term problem as the mineral based oil. They both thicken with extended usage/age.

Full synthetic oils are derived in the laboratory. They are pure, usually nearly clear. I describe mineral based motor oils as a distilled, concentrated product. The impurities need to be removed from the raw petroleum. These oils are therefore less clean and contain many impurities. Again, the problem is really more of theory than practice but the difference does exist.

As an aside, one of the most costly additives (per cc) that goes into motor oils are the dyes or coloring agents!

People repeatedly say that synthetic oils are more stable in a hot engine. I hear that they lubricate better. The answer is yes and no. Oil molecules do not break down, just the additives. Generally, the synthetic oils do not have VI improvers so have less to lose.

There are some properties of synthetic oils that actually may result in a little less wear than with mineral oils. These help increase your gas mileage as well. Due to a reduction of internal friction of the synthetic oil your engine will run a bit cooler. Wear increases as temperature increases, all other things being constant.

A main advantage that the synthetic has over the mineral based oil is the ability to lubricate better at startup. Both types of oil have the similar specifications at 104 F, 212 F and 302 F. It is often the startup viscosity characteristics that separate these oils. In general synthetic oils do not thicken as much on cooling. They have better fluidity as the temperature drops.

A synthetic oil that is labeled as 10W-30 is less honey like as a mineral based 10W-30 motor oil at startup. They both have a thickness of 10 at normal operating temperatures. At 75 F the synthetic is not as thick. At 32 F the difference between the two is even greater. At 0 F the mineral oil works poorly yet the synthetic works fairly well. Just keep the RPM to a minimum.

At temperatures below zero you may not be able to start your car with mineral oils while the synthetic oils may be used to -40 or - 50 F. Oils are so thick that the normal method of viscosity measurement is not possible. Instead we measure if the oil can even be pumped or poured. Again, we are only discussing a single category of oil, the multi-grade 10W-30 oil grade.

I took this excerpt from the web about Mobil 1 oils: They compared a 5W-30 synthetic Mobil 1 oil to a mineral based 10W-30 and a 10W-40 in ice cold conditions. The engine turned over at 152 RPM with the synthetic 5W-30 Mobil 1. The 10W-30 and 10W-40 mineral oils turned over at 45 and 32 RPM respectively. Neither of those engines started.

Motor oil becomes permanently thicker with exposure to northerly winter type weather. This is more of a problem to mineral based oils. Waxes form. This is why it is a bad idea to even store a bottle of oil in a cold garage. It goes bad on the garage shelf just because it is exposed to the cold.

To recap, synthetic oils have similar characteristics as mineral oils at operating temperatures. Often the synthetic oil will however be less honey - like at startup even though it has the same API / SAE rating. Yet the synthetic 10W-30 grade oil is based on a heavier 30 grade oil while the mineral based 10W-30 oil is based on a thinner 10 grade oil. They are both similar at operating temperatures yet the 30 grade based synthetic is actually less thick at startup and less honey - like at low temperatures. This is the opposite of what common sense dictates.

These days many mineral based oils are in fact mixed with some synthetic components. Some synthetics may not be purely synthetic. There may not be a big difference in motor oil quality between the major brands. There is evidence that for general use any main line oil will work well enough, mineral or synthetic.

As one can see this is no easy topic. Are you with me?

AEHaas
Why are these old Chapters being posted in this forum when there are already updated Chapters in the "Motor Oil University" link on the BITOG Home Page?

 

4WD

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16,800
Location
Texas
Again: This is a Mobil guide for Grp4/Grp5 motor oil
There is some level of VM in all … despite combined base stocks to form base oil

DF57E6A2-F6FF-44E0-AF3D-16292238C66A.jpeg
 
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27,485
Location
PNW
I feel like this is bitog 2004 again, BITOG has moved on but these error ridden chapters are being revisited.
 
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Location
Caldwell Idaho
Why is 10w too thick on start up? Will it not fit through the oil passages or between the bearinds at its recommed cold start temps?
 

AEHaas

Thread starter
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Location
Sarasota, Florida
It may be useful to point out that I am doing this to help the novice get a better understanding of basic principals. Please write your own chapters for tribology professors.

"Why is 10w too thick on start up? Will it not fit through the oil passages or between the bearinds at its recommed cold start temps?"
'This is explained in later chapters.

AEHaas
 
Messages
17,238
Location
Upper Midwest
Why is 10w too thick on start up? Will it not fit through the oil passages or between the bearinds at its recommed cold start temps?
It isn’t a 10-weight oil to start with. The finished product meets the cranking and pumpability requirement for an oil that carries a 10W winter rating.

I have no idea why this thread was even begun. It makes no sense.
 
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1,305
Location
canada
It may be useful to point out that I am doing this to help the novice get a better understanding of basic principals. Please write your own chapters for tribology professors.

"Why is 10w too thick on start up? Will it not fit through the oil passages or between the bearinds at its recommed cold start temps?"
'This is explained in later chapters.

AEHaas
I agree with you Doc , your writings may be easier for the novice or newcomers to the forum to help understand ..
 

jurko

Site Donor 2021
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Location
Carson City
A 10W-30 multi-grade mineral based oil is made from a 10 grade oil and has VI improvers added to thicken the product in a 212 F engine. It acts as a 30 grade oil when hot.

Not quite. Motor oils are made from binary and tertiary mixtures of disparate viscosities of various base oils. VII's are then added to achieve the target VI.
Hi Mola.
What is the max. VI you can achieve without using any viscosity improvers?
Amsoil claims that their 10W-30 ACD is formulated without viscosity index improvers.
 

MolaKule

Staff member
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21,908
Location
Iowegia - USA
Hi Mola.
What is the max. VI you can achieve without using any viscosity improvers?
Amsoil claims that their 10W-30 ACD is formulated without viscosity index improvers.
It depends on the individual VI's of the various base fluids used. Amsoil did have the ACD and it did not have any VII's, the VI was based on the totality of the base oils used.
 
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