Thin vs Thick Discussion, Chapter 2

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Motor Oil 102
Chapter two. It gets more difficult.

We left off discussing that a 0W-30 grade oil is not thinner than a 10W-30 oil. They both have the same thickness at operating temperature. The 0W-30 simply does not get as thick on cooling as the 10W-30. Both are still too thick to properly lubricate an engine at startup. Again start up is defined as 75F and anything cooler is even more dramatic.

We will discuss multi-grade oils. Earlier we said that a Straight, or more properly a Single, 30 grade oil has a thickness of 10 at the normal operating temperature of your engine. The Multi-grade oils 0W-30 and 10W-30 also have a thickness of 10 at 212 F.

The difference is at 75 F, your startup temperature in the morning.


Oil type... Thickness at 75 F...Thickness at 212 F

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

Straight 10........30....................... 6

Now you can see that the difference between the desired thickness your engine requires ( = 10 ) is closest to the 0W-30 multi-grade oil at startup. It is still too thick for normal operation. But it does not have far to go before it warms up and thins to the correct viscosity. Remember that most engine wear occurs during the startup interval when the oil is too thick to lubricate properly. It cannot flow freely and therefore cannot lubricate properly. Most of the thick oil at startup actually goes through the bypass valve back to the engine oil sump and not into your engine oil ways. This is especially true when you really step on that gas pedal. You really need more lubrication and you actually get less.

Many engines are ruined because they were run at high RPM before the oil temperature gets up to full operating temperature. Ferrari warns against running their engines at higher RPM until the oil is fully warmed up.

Note that a straight 10 grade oil is also too thick for your engine at startup. It has a thickness of 30. Yet at operating temperatures it is too thin having a thickness of 6. It needs to be around 10. The oil companies have added viscosity index improvers or VII to oils to solve this dilemma. They take a mineral based oil and add VI improvers so that it does not thin as much when it gets hotter. Now instead of only having a thickness of 6 when hot it has a thickness of 10, just as we need.

The penalty is the startup thickness also goes up to 100. This is better than being up at 250 as a straight 30 grade oil though. Oil with a startup thickness of 100 that becomes the appropriate thickness of 10 when fully warmed up is called a 10W-30 grade motor oil. This is NOT as thick as a straight 30 grade oil at startup and it is NOT as thin as a straight 10 grade oil at full operating temperature.

The downside of a mineral based multi-grade oil is that this VII additive wears out over time and you end up with the original straight 10 grade oil. It will go back to being too thin when hot. It will have a thickness of 6 instead of 10. This may be why Porsche (according to some people years ago) did not want a 0W-30 but rather a 10W-30. If the VII wears out the 0W-30 will ultimately be thinner, a straight 0 grade oil. When the VII is used up in the 10W-30 oil it too is thinner. It goes back to a straight 10 grade oil. They are both still too thick at startup, both of them. The straight 0 grade oil, a 5 grade oil and a 10 grade oil are all too thick at startup.

This is just theory however. With normal oil change intervals the VI improver of today will not wear out and so the problem does not really exist. In fact, oils do thin a little with use. This is partly from dilution with blow by gasoline and partly from VI improvers being used up. What is more interesting is that with further use motor oils actually thicken and this is much worse than the minimal thinning that may have occurred earlier. In fact, oxidative thickening is why you cannot just keep using the same oil year after year.

Fully synthetic oils are a whole different story. There is little to no VI improver added so there is nothing to wear out. The actual oil molecules never wear out. You could almost use the same oil forever. The problem is that there are other additives and they do get used up. I suppose if there was a good way to keep oil clean you could just add a can of additives every 6 months and just change the filter, never changing the oil.

I might add that there is evidence that changing the oil filter every other oil change has benefits. They filter better when some of the pores are made smaller by filtering out the larger particles.

When the additives wear out in a synthetic oil it still has the same viscosity. It will not thin as a mineral oil. The fear that some say Porsche had, that oils thin when the VII runs out, is not applicable to these synthetic oils. These oils will always have the correct thickness when hot and will still be too thick at startup as with all oils of all types, regardless of the API / SAE viscosity rating.

Automotive engine manufacturers know these principals of motor oils. They know there is thinning or thickening that will occur. They take these things into account when they write that owners manual. Mineral oil change recommendations will generally include shorter time intervals than those of synthetic oils.

The reality is that motor oils do not need to be changed because they thin with use. It is the eventual thickening that limits the time you may keep oil in your engine. The limit is both time itself (with no motor use) and/or mileage use. The storage of motor oil in your garage, particularly mineral based oils, slowly ages the oil limiting its use later. Do not store huge volumes of oil in your garage that is exposed to extremes of temperature, especially cold temperatures.

End of part two.

AEHaas
 
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This may be why Porsche (according to some people years ago) did not want a 0W-30 but rather a 10W-30. If the VII wears out the 0W-30 will ultimately be thinner, a straight 0 grade oil.
I totally agree with this (y)

Nissan still says in updated TSB's in bold print DO NOT use anything less than a 10W in the 1990-1996 Z32 300ZX.
 

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Straight 10........30....................... 6

Now you can see that the difference between the desired thickness your engine requires ( = 10 ) is closest to the 0W-30 multi-grade oil at startup. It is still too thick for normal operation. But it does not have far to go before it warms up and thins to the correct viscosity. Remember that most engine wear occurs during the startup interval when the oil is too thick to lubricate properly. It cannot flow freely and therefore cannot lubricate properly. Most of the thick oil at startup actually goes through the bypass valve back to the engine oil sump and not into your engine oil ways. This is especially true when you really step on that gas pedal. You really need more lubrication and you actually get less.

Many engines are ruined because they were run at high RPM before the oil temperature gets up to full operating temperature. Ferrari warns against running their engines at higher RPM until the oil is fully warmed up.

Note that a straight 10 grade oil is also too thick for your engine at startup.

There is no straight 10 in J300.

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What you are calling straight 10 would be an SAE 12, on the very cusp of SAE 16.

May I ask why this is being re-hashed when we already have the entire Motor Oil University series on the main page of this site? For example, this "chapter" is covered on the following page:
 

AEHaas

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What some people cannot understand is that these chapters are meant for beginners, in a way that principals are easy to understand as I stated from the start. I am doing these chapters in the best way I can.

"Why would be a straight 10 be too thick at startup if it is able to pump?"
Good question. You will see in later chapters why this is so. For now it is sufficient to say that our example engine is designed to run with an oil having a viscosity of 10. The designers made the engine to run BEST at this single oil viscosity. Best meaning, the optimal combination of wear resistance, good fuel economy, most power, longevity. Any viscosity lower or higher than this may work but in going further away from the designed optimal viscosity has negative consequences.

I am updating the chapters in the Oil University that have been edited several times over the years (by others). I wrote the original chapters almost 20 years ago.

AEHaas
 

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I am updating the chapters in the Oil University that have been edited several times over the years (by others). I wrote the original chapters almost 20 years ago.

AEHaas

They were edited by formulators and engineers to be more accurate, and this was quite recently, you aren't going to improve on that. If this thread and the previous one are any indication, you are in fact attempting to impose edits that are regressive.

While I applaud the effort, I really must insist that you consider WHY those articles were revised by people who actually work in the industry and what they hoped to accomplish in doing so. This was a board-level effort, not the product of one person. The entire site agreed that these articles needed to be revised and improved to contain more accurate material and a SERIOUS amount of effort was put forth by numerous professionals who collaborated to make those changes.
 

AEHaas

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When I was a surgeon in training there were professors who explained things to patients. After the professors left, often patients were wholely confused. I would go back and explain things again but in a manor they were able to understand. Too often highly educated people are not able to leave out details that only confuse those with less education. To be able to educate others you have to be able to see things from their level. Only then can you teach them anything.

My goal at this web site is to read and learn from those who know more than I do. Another goal is to educate those who may need help, in a way they can understand. If you can edit my chapters to make them easier to elucidate basic principals then I applaud you. Go for it.

AEHaas
 

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When I was a surgeon in training there were professors who explained things to patients. After the professors left, often patients were wholely confused. I would go back and explain things again but in a manor they were able to understand. Too often highly educated people are not able to leave out details that only confuse those with less education. To be able to educate others you have to be able to see things from their level. Only then can you teach them anything.

My goal at this web site is to read and learn from those who know more than I do. Another goal is to educate those who may need help, in a way they can understand. If you can edit my chapters to make them easier to elucidate basic principals then I applaud you. Go for it.

AEHaas

Sure, and I appreciate that approach, but I think the revisions made did try and retain the easy readability while still keeping things factually correct. I took advantage of the encouragement for members to proof-read the revised articles when they were being drafted, so being part of that process and aware of the immense amount of work that went into them perhaps if there are going to be some suggested edits to improve readability, these revised versions are used as the foundation?

This would help avoid things like your SAE 10 example above, a grade that doesn't exist. So, while I get what you are trying to say, doing it with a grade that doesn't appear in J300 doesn't do anyone any favours and in fact will cause more confusion than anything. The updated articles have 8, 12 and 16 in them, all now ratified grades below SAE 20.
 

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Lower grade schools have been dropping spelling, choosing to concentrate on the meaning of the words. Spelling is never corrected nor mentioned. The educators figure that the student can learn spelling on their own later on. Let’s learn the meaning of the word now and worry about the details later.

As I stated in chapter one I would use examples that reveal the principal rather than be totally accurate. I believe that 10 - 20 - 30 - 40 is easier to use as examples than the J300 correct 8 - 12 - 16 - 20 - 30 - 40. Things are easier to visualize in groups of 10, at least for me.

I love teaching.

AEHaas
 

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As I stated in chapter one I would use examples that reveal the principal rather than be totally accurate. I believe that 10 - 20 - 30 - 40 is easier to use as examples than the J300 correct 8 - 12 - 16 - 20 - 30 - 40. Things are easier to visualize in groups of 10, at least for me.

I prefer to start with factually correct information. If you find the nuance of the 8, 12 and 16 grades confusing why not simply skip them and start with 20, 30, 40? Just bump your reference viscosity up a few cSt to be an SAE 20 and then you don't have to make up a grade that is going to cause confusion later on.

AEHaas said:
I love teaching.
Nothing wrong with that. Both my parents are educators, my dad a university prof, my mom taught special ed, so she's intimately familiar with teaching people who have a difficult time learning and dealing with concepts. However, not once do I recall her intentionally changing something to be factually incorrect on the off chance it might make it easier to understand, she'd simply work the concepts around it to make it easier to understand. I also have two sisters that have either taught, or teach presently.
 
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Motor Oil 102
Chapter two. It gets more difficult.

We left off discussing that a 0W-30 grade oil is not thinner than a 10W-30 oil. They both have the same thickness at operating temperature. The 0W-30 simply does not get as thick on cooling as the 10W-30. Both are still too thick to properly lubricate an engine at startup. Again start up is defined as 75F and anything cooler is even more dramatic.
Pretty much any oil viscosity provides proper lubrication at a 75F start-up because at that temperature they all will be 100% pumpable by the PD oil pump. Only time any oil doesn't provide proper lubrication is when it's too cold for the oil pump to pump at 100% (ie, the oil pumpability has degraded), and that's certainly not at 75F ambient temperature.
 
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We will discuss multi-grade oils. Earlier we said that a Straight, or more properly a Single, 30 grade oil has a thickness of 10 at the normal operating temperature of your engine. The Multi-grade oils 0W-30 and 10W-30 also have a thickness of 10 at 212 F.
It's not a "thickness" ... it's a viscosity of 10 cSt. Talking with no units isn't accurate and is confusing.
 
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When the additives wear out in a synthetic oil it still has the same viscosity.
There are plenty of VIIs in full synthetic to make them shear with use. They may not shear as badly, but they still shear down in viscosity.

The reality is that motor oils do not need to be changed because they thin with use. It is the eventual thickening that limits the time you may keep oil in your engine.
Go read the VOA and UOA forums for awhile. Compare the same oil's VOA to its UOA, and you will see that pretty much every oil will shear and the viscosity will be less from use. Fuel dillution will also decrease the viscosity. I don't think I've ever seen an oil actually get thicker in viscosity than the virgin oil. Maybe if it was ran way beyond a reasonable OCI and it started to turn to sludge.
 

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There are plenty of VIIs in full synthetic to make them shear with use. They may not shear as badly, but they still shear down in viscosity.


Go read the VOA and UOA forums for awhile. Compare the same oil's VOA to its UOA, and you will see that pretty much every oil will shear and the viscosity will be less from use. Fuel dillution will also decrease the viscosity. I don't think I've ever seen an oil actually get thicker in viscosity than the virgin oil. Maybe if it was ran way beyond a reasonable OCI and it started to turn to sludge.
There have been a couple of them, but they are few and far between. Viscosity loss dominates, most of it due to fuel dilution, which appears to be getting worse with the DI mills.
 
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In many paper I read, viscosity is often referred to as the thickness of a fluid.
So let's not nitpick here.
Then at least just don't say "10" ... explain that it's a unit of viscosity - Ie, 10 cSt. If I say "a thickness of 10", is it 10 microns or 10 cP or 10 cSt or 10 SSUs or 10 whats?
 
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I might add that there is evidence that changing the oil filter every other oil change has benefits. They filter better when some of the pores are made smaller by filtering out the larger particles.
That is not always true. Hummel+Mann/Purolator showed that oil filters can become less efficient as they load up and the delta-p across the media increases and dislodges already captured particles. Then near the end of their useful life, they quickly become more efficient right before they totally clog and go into bypass. A condition you really don't want an oil filter to do. I never see you in the oil filter forum. ;) IMO, oil filters are off topic in an oil article.
 
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