Thin vs Thick Discussion Chapter 1

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A few things I keep hearing again and again:
“The flow will be proper because its a positive displacement oil pump. The flow will always be exactly related to the RPM. It makes no difference what oil weight you use” This is Wrong.
“0-30 is too thin, my engine requires a 10-30 oil.” Wrong again.

Statements as these are why I wrote these chapters almost 20 years ago. I feel it may be a good time to republish the original articles (with some updated editing) so here goes.

Chapter One - Motor Oil 101 (Revisited)

I think it is time to go over passenger car automotive engine oils in detail (again). Note that what I am writing is to the best of my knowledge and experience.

This is a very difficult topic to comprehend. Everybody including good mechanics think they are experts in this field but there are often misconceptions. Too often what I hear is the opposite of the truth. It is however easy to see how people get mixed up as there is always some truth to the misconception.

Please forgive me if I am too wordy or even verbose at times. I will be redundant for certain. This will be in areas that people have to hear things over and over again to get it right. Some will never be able to understand these concepts unfortunately. I will try to minimize technical terms and be somewhat vague rather than exact. I will round and average numbers to make the point simple rather than mathematically exact.

Thickness has the same meaning as viscosity. Viscosity is a measure of the resistance of a fluid (liquid or gas) to flow. Fluids with high viscosity, such as molasses, flow more slowly than those with low viscosity, such as water. Again, I am trying to explain general principals as I know them.

The greatest confusion is because of the way motor oils are labeled. It is an old system and is confusing to many people. I know the person is confused when they say that a 0W-30 oil is too thin for their engine because the old manual says to use 10W-30. This is wrong.

More confusion occurs because people think in terms of the oil thinning when it gets hot. They think this thinning with heat is the problem with motor oil. It would be more correct to think that oil thickens when it cools to room temperature and THIS is the problem. In fact this is the problem. It is said that 90 percent of engine wear occurs at startup. If we are interested in engine longevity then we should concentrate our attention at reducing engine wear at startup.

Also, cold is defined as 75F, not sub zero temperatures. Oil is “cold” at room temperature. Surely colder than this is even more difficult on engines but wear occurs much more in cold ( 75F ) engines than when they are up to operating temperature at around 212F.

Oils are chosen by the manufacturer to give the right thickness at the normal operating temperature of the engine. I will say this average oil temperature is 212 F, the boiling point of water. On the track that temperature is up to 302F. It is important to realize that these are two different operating environments and require different oils. In both cases the oil functions less well at room temperature than at operating temperature.

I will discuss driving around town first. Everything I say will be based on these conditions. At a later time I will discuss track conditions. Everything I say will be as accurate as possible without looking everything up and footnoting. I am trying to be general not ultra specific.

One thing that is less important is the ambient temperature. Older automotive owner manuals often recommended one oil for the summer and another for the winter. This is still necessary for air cooled engines but is no longer a consideration in pressurized water cooled engines. These engine blocks are kept at around 212 F all year round when the engine gets up to the designed operating temperature. The oil is around the same temperature as well. This allows for a single grade oil all year round. Again, this is not the same as on the track where the coolant temperature may be slightly higher and the oil temperature is much higher.

Please forget those numbers on the oil can. They really should be letters as AW-M, BW-N or CW-P. The fact that we are dealing with a system of numbers on the can makes people think that they represent the viscosity of the oil inside the can. The problem is that the viscosity of oil varies with its temperature. A “30” grade oil has a viscosity of 3 at 302 F ( 150 C ) and thickens to 10 at 212 F ( 100 C ). It further thickens to a viscosity of 100 at 104 F ( 40 C ) and may be too thick to measure at the freezing point of 32 F ( 0 C ).

Oils are divided into grades (not weights) such as a 20, 30 or 40 grade oil. This represents the viscosity range at operating temperature. But it is NOT the actual viscosity as we shall see. The issue is that viscosity is temperature dependent. Let’s look at a 30 grade oil and how the viscosity of this grade of oil varies with temperature.

People think that the “W” on the can means winter. It does not. One should not think that the first number on the oil can is for ice cold weather operation. It may be better to think that it represents the resistance to thickening when the engine cools to ROOM temperature. The first number gives base stock information on which the oil is formulated, designed.

Now let’s look at a 30 grade oil (often referred to as a 30 “weight” oil). This in your average passenger car engine.

Temperature ( F )....Thickness

302...........................3
212..........................10
104..........................100
32..........................250 (rough estimate)

The automotive engine designers usually call for their engines to run at 212 F of both oil and water temperature with an oil thickness of 10. This is the viscosity of the oil, NOT the weight or grade as labeled on the oil can. Let me say this again as it is very important here: This is the viscosity of the oil, NOT the weight or grade as labeled on the oil can. I want to stay away from those numbers as they are confusing. We are talking about oil thickness, not oil can labeling. This will be discussed later. Forget the numbers on that oil can for now. We are only discussing the thickness of the oil that the engine requires during normal operating conditions.

The engine is designed to run at 212 F at all external temperatures from Alaska to Florida. You can get in your car in Florida in September and drive zig-zag to Alaska arriving in November. The best thing for your engine would be that it was never turned off, you simply kept driving day and night. The oil thickness would be uniform, it would always be 10. In a perfect world the oil thickness would be 10 at all times and all temperatures. And the wear would be nearly Zero.

If the thickness of oil was 10 when you got in your car in the morning and 10 while driving it would be perfect. You would not have to warm up your engine. You could just get in the car and step on the gas. There would be little wear and tear on your engine, almost none. Unfortunately the world is not perfect.

The night before when you drove home from work the car was up to the correct operating temperature and the oil was the correct thickness, 10. Over night the engine cooled to room temperature and the oil thickened. It is 75 F in the morning now (I do live in Florida). The oil thickness is now around 150. It is too thick to lubricate an engine properly designed to run with an oil having a thickness of 10.

The wear is highest at the “cold” ( 75 F ) temperature when you first start your engine. The wear gradually decreases as your engine oil warms up to operating temperature, around 212F. Note: Many think the engine is warmed up within minutes as the water temperature warms up fast. In reality it takes up to 30 minutes for the oil temperature to warm from start up ( 75 F ) to the normal operating temperature. Do not be fooled. As most trips are shorter than 30 minutes the engine rarely gets up to full operating temperature. More water and fuel is retained in the oil and this is not a good thing.

It is time to introduce the concept of lubrication. Most believe that pressure = lubrication. This is false. Flow = lubrication. If pressure was the thing that somehow lubricated your engine then we would all be using 90 grade oil. Lubrication is used to separate moving parts, to keep them from touching. There is a relationship between flow and separation. The pressure at the bearing entrance is irrelevant.

In fact the relationship between pressure and flow is in opposition. If you change your oil to a thicker formula the pressure will go up. It goes up because the resistance to flow is greater and in fact the flow must go down in order for the pressure to go up. They are inversely related. Conversely if you choose a thinner oil then the pressure will go down. This can only occur if the flow has increased.

It seems then (in my opinion) that we should all be using the thinnest oil money can buy. This is partly true. Let me use my old 575 Ferrari Maranello as an example. I drove this car around town. The manual of this car states the target pressure is 75 PSI at 6,000 RPM. The gold standard, according to some of us, is that all engines should have a pressure of 10 PSI for every 1,000 RPM of operation, not more, not less. After all, you do need some pressure to move that oil along, but only enough pressure, not more. More pressure is not better, it can only result from the impedance of oil flow. Remember that oil flow is the thing that does the lubricating.

Note that Ferrari is not saying what thickness of oil to use. That can only be determined by experimentation. My engine oil temperature was running around 185 F as I drove around town on a hot Florida summer day. I have found that the thinnest oil I can buy that is API / SAE certified is Mobil 1’s thinnest oil. Even with this oil I get 80 PSI at 2,000 RPM. It is too thick for my application yet it is the thinnest oil money can buy. If I was on a hot Florida track in mid-summer the oil temperature would probably get up to 302 F. I will guess that the pressure would only be 40 PSI at 6,000 RPM. The oil I am using would not meet the requirement of 75 PSI at 6,000 RPM from Ferrari. I would have to choose a thicker oil for this racing situation. The oil I use now would be too thin at that very high temperature. (This is only partly true. Higher RPM running engines use thinner and thinner oils to get more and more flow. I will discuss this later).

High flow does more than lubricate. It is one of the things used to cool the hottest parts of your engine, the pistons, valve areas and bearings. This cooling effect is as important as lubrication in your engine. If your engine is running hot you may need to use a thinner oil. The flow will increase and so will the cooling. This is even more important in the racing condition.

Let us go back to the Ferrari manual. My older 550 Maranello only specified 5W-40 Shell Helix Ultra as the oil to use in all conditions. This car was designed for racing. As it turns out Ferrari now recognizes that not every owner races their cars. The newer 575 manual now states to use 0W-40 for around town situations even though Shell does not make this oil in the Helix Ultra formulation at this writing. They also recommend the 5W-40 by Shell if you insist on the Shell product. It is also the recommended oil for most racing conditions.

Ferrari recommends Helix Ultra Racing 10W-60 “for hot climate conditions racing type driving on tracks”. Note that they realize the difference between the daily urban driver like me and the very different racing situation. These are widely different circumstances. I want to emphasize that they only want you to use this oil while racing in “hot climate conditions”. If you are racing in Watkins Glen up north use the 5W-40. If you are racing in Sebring in the middle of the Florida summer use the 10W-60. Around town in any climate, use the 0W-40.

It is time to dispel the notion that 0W-30 oil is too thin when our manual calls for 10W-30. A 0W-30 is always the better choice, always. The 0W-30 is not thinner. It is the same thickness as the 10W-30 at operating temperatures. The difference is when you turn your engine off for the night. Both oils thicken over the evening and night. They both had a thickness, a viscosity of 10 when you got home and turned your engine off. That was the perfect thickness for engine operation.

As cooling occurs and you wake up ready to go back to work the next day the oils have gotten too thick for your engine to lubricate properly. It is 75 F outside this morning. One oil thickened to a viscosity of say 90. The other thickened to a viscosity of 40. Both are too thick in the morning at startup. But 40 is better than 90 on start up. Your engine wants the oil to have a thickness of 10 to work properly. You are better off starting with the viscosity of 40 than the honey - like oil with a viscosity of 90.

I repeat: More confusion occurs because people think in terms of the oil thinning when it gets hot. They think this thinning with heat is the problem with motor oil. It would be more correct to think that oil thickens when it cools to room temperature and THIS is the problem. In fact this is the problem. This is why multi-viscosity oils were developed.

This is the end of lesson number one.

AEHaas
 

4WD

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There will be plenty of folks get into the hydraulic/viscometric debate … part of my job as well.
But, to decide what W means lands with industry committees … Formulator companies follow:

 
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W-rating only says that an oil meets certain minimum pumpability requirements at -40C, -35C,-30C,etc and even then the range that's acceptable can be fairly wide, and even at room temp a 10w30 that's resource conserving may actually be thinner than a 0w30 that's A3/B4 because SAE viscosity is a fairly wide range, and different base stocks and different VIIs can make the oil have wildly different viscosity curves and still nail a particular W rating and operating viscosity.
 
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Good read and thanks for the post. Explains why I use 0w-20 in South Carolina!

Interesting that most "racing" oil sold in the U.S. for professional racing teams comes in 0W-xx or 5w-xx ratings.

Another consideration with wear and cold engines is the fact that moving parts have not reached their designed clearances when cold.
 
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South Carolina
W-rating only says that an oil meets certain minimum pumpability requirements at -40C, -35C,-30C,etc and even then the range that's acceptable can be fairly wide, and even at room temp a 10w30 that's resource conserving may actually be thinner than a 0w30 that's A3/B4 because SAE viscosity is a fairly wide range, and different base stocks and different VIIs can make the oil have wildly different viscosity curves and still nail a particular W rating and operating viscosity.
This is why I consider Viscosity Index such an important measure.
 
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Are you sure on the part where you mentioned the W doesn’t stand for winter? Because when I joined here I knew little about oil and thought it meant weight which is what they taught us in school but found out it was wrong. Everyone here says it means winter which is what I now believe. Unless I misunderstood what you were trying to say there.
 
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South Carolina
Are you sure on the part where you mentioned the W doesn’t stand for winter? Because when I joined here I knew little about oil and thought it meant weight which is what they taught us in school but found out it was wrong. Everyone here says it means winter which is what I now believe. Unless I misunderstood what you were trying to say there.
I caught that too. I think he missed this part with his edit. This piece was written probably 15 years ago.
 

4WD

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Good read and thanks for the post. Explains why I use 0w-20 in South Carolina!

Interesting that most "racing" oil sold in the U.S. for professional racing teams comes in 0W-xx or 5w-xx ratings.

Another consideration with wear and cold engines is the fact that moving parts have not reached their designed clearances when cold.
Good point. Even common brands like Mobil 1 sell the racing oils at a whole new price point … pretty high end material to formulate 0w50 and then the price for the R word …
On the other hand … M1 0w40 is very cheap even with A40 and other … 15w50 is cheap too …
 
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Nissan tells me in their 1990-1996 Z32 FSM to not go below a 10W-30 and not to use a 5W 30 unless you're operating the car in below freezing temperatures. It forbids the use of a 5W-20. Years later,Nissan issued a TSB saying "Use 5W-30 in all Nissan vehicles except 300ZX". To this day Nissan still specs 10W30/10W40 under normal operating conditions and 15W-50/20W-50 under racing or extended high speed conditions.

Nissan obviously wants a thick base oil on startup for the VG30DE/TT engines.

As soon as I get her back from the body shop she's getting a fresh belly full of PHM (dino juice) 10W-40. Everyone here knows that I♥️Molly;)
 

OVERKILL

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A few things I keep hearing again and again:
“The flow will be proper because its a positive displacement oil pump. The flow will always be exactly related to the RPM. It makes no difference what oil weight you use” This is Wrong.
“0-30 is too thin, my engine requires a 10-30 oil.” Wrong again.

Statements as these are why I wrote these chapters almost 20 years ago. I feel it may be a good time to republish the original articles (with some updated editing) so here goes.

Assuming the relief on the pump is closed, the flow will be the same regardless of the viscosity relative to RPM. In fact a heavier oil will flow ever so slightly more (again, the relief being closed) because it creates less "slip" in the pump.

When the relief opens, then flow will of course be reduced. If you know what the relief pressure is for your oil pump, this is easy enough to monitor with an oil pressure gauge.

This comes back to simply using an appropriate lubricant for the anticipated ambient conditions.
People think that the “W” on the can means winter. It does not.

No, it actually does in fact mean Winter.

Oil 101 and the like were revised to improve accuracy. This is why those pages were redone with the help of formulators and engineers.

Savant Labs offer testing according to (Society of Automotive Engineers) SAE J300 to determine an engine oil’s SAE viscosity grade. Four viscosity tests determine the multi-grade parameters. A multi-grade oil’s viscosity grade is often expressed as #W##, for example 5W30 or 0W20. The “W” in the viscosity grade stands for “winter”.

SAE J300 is the standard for automotive oils used in combustion engines (crankcases). These are complex oils that can be divided into three categories: winter, high-temperature and multi-grade.

The winter (W) group measures the cold-cranking and pumping ability of oil temperatures as low as minus 10 to minus 40 degrees C. They are measured in centipoise (cP). However, SAE viscosity grades 0W to 20W are also measured in centistokes (kinematic viscosity) at 100 degrees C as part of the high-temperature or operating-temperature group.

The viscosity grade of a lube oil is determined by the Society of Automotive Engineers (SAE). Oils can be separated into multigrade oils and monograde oils. Multigrade oils must fulfill two viscosity specifications, their viscosity grade consists of two numbers, e.g. 10W-40: 10W refers to the low-temperature viscosity ("Winter"), 40 refers to the high-temperature viscosity ("Summer"). Currently, most automotive engine oils are multigrade oils, while oils for restricted usage, e.g. for seasonally used engines like lawn mowers, are often monograde oils. While the two numbers specify the SAE viscosity grade, the viscosity index shows the temperature related change of viscosity.

Motor oil viscosity is commonly measured at lower and higher temperatures. The properties of the oil at lower temperatures define the first part of the motor oil grade. In the example of a 0W-20, the “0W” part of the grade is related to the measurement of viscosity at low temperatures as defined by SAE J300 (and the “W” stands for Winter – relating it to low temperature performance). The better the oil performs at lower temperatures, the lower the number before the W. The numbers are ranges defined by SAE J300, so zero doesn’t mean zero performance; it means the oil performs better at lower temperatures and flows easier than oils that fall in 5W, 10W, 20W, etc. ranges.

Overview: ASTM D5893 -Cold cranking viscosity or CCS - is used to simulates the viscosity of oil in crankshaft bearings during cold temperature start up. This is another viscosity requirement specified in SAE J300 standard which defines the viscosity grade of the oil. CCS viscosity helps define the “W” or “winter” part of a multigrade oils. As with kinematic viscosity, J300 defines mandatory ranges which must be met – one must claim the lowest “W” level met. For a 5W-30 engine oil, numbers in the red, indicate the oil does NOT meet the requirements to be labeled a 5W oil.

Note: This chart only includes viscosity at 100°C for the summer grade. It excludes winter grades designated by SAE ##W, it must meet additional low temperature testing listed on the corresponding SAE J300 or J306 viscosity classification table (not shown here).

ngine lubricants are classified using the Society of Automotive Engineers (SAE) J300 oil viscosity classification system. Multi-grade engine lubricants, such as SAE 5W-30 or 10W-30, must meet both low temperature and high temperature viscosity requirements. In a SAE 5W-30 engine lubricant:

  • “5W” refers to low-temperature viscosity (the "W" denotes winter) and is an indication of how easily the lubricant will flow in cold start-up conditions. At a given temperature a 5W lubricant has a lower viscosity than a 10W lubricant so flows faster during critical start-up. This is sometimes referred to as cold cranking simulator (CCS) viscosity.
  • “30” refers to the high temperature viscosity at 100°C, therefore replicating an engines operating temperature.
Hopefully Chevron, Lubrizol, Castrol...etc are authoritative enough sources to put this one to rest.
 

AEHaas

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‘A useless point to debate in reality.... but....
Interesting that the 167 page governing document:
Engine Oil Licensing and Certification System
API 1509
EIGHTEENTH EDITION, JUNE 2019
never once mentions the word “Winter.”
I spoke to an SAE engineer some years ago (when I was a member) and asked what the W stood for. He said no word in particular, that it could have been any other letter.
 

4WD

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‘A useless point to debate in reality.... but....
Interesting that the 167 page governing document:
Engine Oil Licensing and Certification System
API 1509
EIGHTEENTH EDITION, JUNE 2019
never once mentions the word “Winter.”
I spoke to an SAE engineer some years ago (when I was a member) and asked what the W stood for. He said no word in particular, that it could have been any other letter.
Then buy your oil from him … oil companies in the US and EU (how I buy mine) call it a winter rating …
If that does not fit your narrative … so be it …
BTW: hydraulics and rheology are parts of my job … and have never seen more exaggeration on the effects of viscosity than what this site brings …
 
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A few things I keep hearing again and again:
“The flow will be proper because its a positive displacement oil pump. The flow will always be exactly related to the RPM. It makes no difference what oil weight you use” This is Wrong.
With a PD pump, all of the oil leaving the pump will go through the engine, and only If the PD starts going into pressure relief, then that is when not all the oil leaving the pump will go through the engine. With increased RPM there is an increase in flow output to the engine oiling system, even if the pump is in pressure relief - see graph below. Exactly how much pump "slip" the pump has, the viscosity of oil being pumped (thicker oils pump better due to less slip) and the overall pumping efficiency of the pump will determine just how much flow roll-off there is before the pump hits pressure relief, and also while in pressure relief dependent on the relief valve design.

A PD pump certainty does ensure that the flow will be proper. The only time it's not proper is if there is a lack of lubrication, and that pretty much only happens when: 1) The PD pump is severely worn out, or 2) The oil is so cold and thick that it's not pumpable and can't be pumped. If the oil has total pumpability and the pump is healthy then there will always be adequate lubrication.

Oil Flow Requirements Chart.jpg
 

OVERKILL

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‘A useless point to debate in reality.... but....
Interesting that the 167 page governing document:
Engine Oil Licensing and Certification System
API 1509
EIGHTEENTH EDITION, JUNE 2019
never once mentions the word “Winter.”
I spoke to an SAE engineer some years ago (when I was a member) and asked what the W stood for. He said no word in particular, that it could have been any other letter.

I don't think it's a useless point to debate at all, you stated, rather authoritatively, that it didn't stand for "Winter", yet numerous oil companies and additive companies state that it in fact does.

The 620 page Chevron Products Digest has the following in its glossary:

Screen Shot 2021-04-03 at 2.20.35 PM.png


This page from Mobil Industrial is similar:

1617475428244.png


And the Society of Tribologists and Lubrication Engineers:
Screen Shot 2021-04-03 at 2.47.20 PM.png


From the DOI:
Screen Shot 2021-04-03 at 3.01.46 PM.png


So clearly, in the parlance of most of the companies actually involved in lubricant formulation and tribology, it is widely understood that the W does in fact stand for "Winter".
 

4WD

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Location
Texas
With a PD pump, all of the oil leaving the pump will go through the engine, and only If the PD starts going into pressure relief, then that is when not all the oil leaving the pump will go through the engine. With increased RPM there is an increase in flow output to the engine oiling system, even if the pump is in pressure relief - see graph below. Exactly how much pump "slip" the pump has, the viscosity of oil being pumped (thicker oils pump better due to less slip) and the overall pumping efficiency of the pump will determine just how much flow roll-off there is before the pump hits pressure relief, and also while in pressure relief dependent on the relief valve design.

A PD pump certainty does ensure that the flow will be proper. The only time it's not proper is if there is a lack of lubrication, and that pretty much only happens when: 1) The PD pump is severely worn out, or 2) The oil is so cold and thick that it's not pumpable and can't be pumped. If the oil has total pumpability and the pump is healthy then there will always be adequate lubrication.

View attachment 52586
$10 royalty for the graph Zee ! (PayPal is good) … 😷
 
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‘A useless point to debate in reality.... but....
Interesting that the 167 page governing document:
Engine Oil Licensing and Certification System
API 1509
EIGHTEENTH EDITION, JUNE 2019
never once mentions the word “Winter.”
I spoke to an SAE engineer some years ago (when I was a member) and asked what the W stood for. He said no word in particular, that it could have been any other letter.
See page 4: http://www.lelubricants.com/wp-content/uploads/pdf/news/White Papers/simple_viscosity.pdf
 

OVERKILL

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This statement is also wildly incorrect in the context of a PD pump:

AEHaas said:
In fact the relationship between pressure and flow is in opposition. If you change your oil to a thicker formula the pressure will go up. It goes up because the resistance to flow is greater and in fact the flow must go down in order for the pressure to go up. They are inversely related. Conversely if you choose a thinner oil then the pressure will go down. This can only occur if the flow has increased.

Flow stays the same (assuming the relief is closed) but pressure will go up if viscosity increases. Conversely, flow stays the same and pressure will go down if viscosity decreases.

Again, this is all in the context of a PD pump that isn't on the relief and bypassing back into the inlet (pumps don't bypass into the pan), which can be observed on this exploded view of a GM oil pump:
1617477446005.png


The same on the Ford modular crank-driven pump:
1617477747860.png
 
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