Simple oil question

[BlackBeard]

I've been an oil fanatic for some time now but I can't get one theory though my head. I'm sure someone here can explain it in simple terms for me. I'll get to the point:

5w-20 oil is very thin. Almost a consistency of water

10-49 oil is very thick compared to 5w-20. So in my mind the number 20 stands for a thinner index than the number 40w,
Here is where I get confused. When the oil is cold it's rated as a 10, when hot it's rated at a 40 weight. But in real world when you have that cold oil it's much much thicker than when it's hot. So how does the number system work because it doesn't make sense to me. And go ahead and get technical I've been a mechanic and engineer most my life this is just one theory that has me stumped. I like to visualize answers in my mind and I can't get over the fact that a 29 weight oil is so thin and a 40 weight so heavy yet when Cold that 10-40 is no where near 5-20 consistency even though it's cold rated at a. 10 weight

 

[Nick1994]

The first and second numbers have absolutely no correlation to each other. Nothing to do with each other.

The first number is basically the pumpability when cold
The second number is the oil's viscosity when warmed up

And no, a 20 weight oil is absolutely not the "consistency of water"

 

[Toaster_Jer]

Best advice I can think of, click at the top for Pennzoil Q&A then off to the right click on Putting the Simple Back into Viscosity and read it over. Then ask any questions you might have.

 

[jorton]

Oh. 5w-20, 10w-40. None on these numbers are viscosity numbers. They are oil grade numbers.

Grade 10w-40 is about viscosity 800 when cold, but it is still pumpable. And it's about viscosity 14 at 212 f.

ref: http://www.viscopedia.com/viscosity-tables/substances/engine-oil/

 

[Rand]

the average 5w20 is aprox 8.5x thicker than water.

the average 5w30 is aprox 10.5x thicker than water.


The first number is the winter rating.. the second number is the viscosity grade at operating temperature.

one of the measurements of viscosity is cSt

 

[Kuato]

Originally Posted By: BlackBeard
I've been an oil fanatic for some time now but I can't get one theory though my head. I'm sure someone here can explain it in simple terms for me. I'll get to the point:

5w-20 oil is very thin. Almost a consistency of water

10-49 oil is very thick compared to 5w-20. So in my mind the number 20 stands for a thinner index than the number 40w,
Here is where I get confused. When the oil is cold it's rated as a 10, when hot it's rated at a 40 weight. But in real world when you have that cold oil it's much much thicker than when it's hot. So how does the number system work because it doesn't make sense to me. And go ahead and get technical I've been a mechanic and engineer most my life this is just one theory that has me stumped. I like to visualize answers in my mind and I can't get over the fact that a 29 weight oil is so thin and a 40 weight so heavy yet when Cold that 10-40 is no where near 5-20 consistency even though it's cold rated at a. 10 weight


Yeah it can be confusing. Take a 0w20 and a 0w40. Both will meet the requirements of a 0w oil when it is cold. The first number can be read "performs at this weight at the specified temperature". The second number can be read "performs at this weight at operating temperature". As stated earlier the "w" specifies a winter weight oil.

As they warm up and get to operating temperature, the 0w20 will be much thinner than the 0w40.

So with your comparison, the 10w40 is thicker at both ends, behaving as a 10w at low temperatures and a 40 weight at operating temperature, vs the 0w20.

 

[OVERKILL]

Originally posted here:
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3515622/Oil_change_question

Updated a little.

The number in front of the W is not a representation of an SAE 5 "when cold", which doesn't exist as a motor oil grade, neither does a 10 or a 15, all of which are a xW classifications. The same goes for a 0. Is there an SAE 0? No. The SAE grading system for oils under the non-W classification starts at SAE 20 (or did, it is now 16).

Just as an example here, Mobil 1 0w-40 and Mobil 1 0w-20 both carry the 0w designation. Which means they meet the cold temperature performance requirements for that classification. This classification is simply a set of limits for MAXIMUM viscosity at -40C and -35C respectively. That is the ONLY thing those two oils have in common:

M1 0w-20:
Visc@100C: 8.7cSt
Visc@ 40C: 44.8cSt
MRV@ -40C: 9,200cP

M1 0w-40:
Visc@100C: 13.5cSt
Visc@ 40C: 75.0cSt
MRV@ -40C: 31,000cP


Is 9,200cP close to 31,000cP? Nope. But they are both under 60,000cP at -40C (and under 6,200cP for CCS @ -35C), so they both get to carry the 0w designation. There is no temperature that M1 0w-40 is even CLOSE to the same viscosity as the 0w-20.

You'll notice the 0W and 5W designations have the exact same visc minimums @ 100C, with no maximums for 100C or HTHS. You'll also notice the distinct absence of an SAE 5, 10 and 15 grade on the chart wink Those grades only exist as ISO hydraulic oil grades, not engine oils.

 

[Dyusik]

Cold flow ratings are at -x degrees. The 20w20 will be thinner than 0w40 at warmer temps, to put it in perspective. The chart above, notr at what temps the "w" ratings are at.

 

[eljefino]

In England (?) they used to call diesel "32 second oil" because a certain amount at a certain temp would drip through a cup with a certain size orifice at the bottom until it was all gone. Kerosene was "28 second oil" because it was thinner. You can imagine motor oil dripping through a hole and being measured similarly.

Oil has an "absolute viscosity" at temp, which is measured in centistokes, which is translated into SAE grade. Typically room temperature oil is many hundreds of centistokes, but 100'C oil is 8-12. "Everybody" would like to move the room temp viscosity down, without compromising anything else (eg wear.)

So they test oil when its cold and when it's at running temp, and you get your two numbers that way. Some has a "wider spread" than others, by design.

 

[alarmguy]

Originally Posted By: OVERKILL
Originally posted here:
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3515622/Oil_change_question

Updated a little.

The number in front of the W is not a representation of an SAE 5 "when cold", which doesn't exist as a motor oil grade, neither does a 10 or a 15, all of which are a xW classifications. The same goes for a 0. Is there an SAE 0? No. The SAE grading system for oils under the non-W classification starts at SAE 20 (or did, it is now 16).


Just as an example here, Mobil 1 0w-40 and Mobil 1 0w-20 both carry the 0w designation. Which means they meet the cold temperature performance requirements for that classification. This classification is simply a set of limits for MAXIMUM viscosity at -40C and -35C respectively. That is the ONLY thing those two oils have in common:

M1 0w-20:
Visc@100C: 8.7cSt
Visc@ 40C: 44.8cSt
MRV@ -40C: 9,200cP

M1 0w-40:
Visc@100C: 13.5cSt
Visc@ 40C: 75.0cSt
MRV@ -40C: 31,000cP


Is 9,200cP close to 31,000cP? Nope. But they are both under 60,000cP at -40C (and under 6,200cP for CCS @ -35C), so they both get to carry the 0w designation. There is no temperature that M1 0w-40 is even CLOSE to the same viscosity as the 0w-20.

You'll notice the 0W and 5W designations have the exact same visc minimums @ 100C, with no maximums for 100C or HTHS. You'll also notice the distinct absence of an SAE 5, 10 and 15 grade on the chart wink Those grades only exist as ISO hydraulic oil grades, not engine oils.


Great Post.

 

[AirgunSavant]

You guys stepped up with some QFI for the OP........ Great!
QFI is my lingo for " Quality Free Information "

 

[440Magnum]

Originally Posted By: BlackBeard
I like to visualize answers in my mind and I can't get over the fact that a 29 weight oil is so thin and a 40 weight so heavy yet when Cold that 10-40 is no where near 5-20 consistency even though it's cold rated at a. 10 weight



I'll offer up my usual explanation, which starts with "you're thinking of it all backward." Stop thinking of the oils at room temperature.

Any oil's "natural state" is at engine operating temp, say 200 degrees F, +/- a bit. The number after the "w" in 0w40 or 5w20 is intended to be a representation of the oil's viscosity AT OPERATING TEMPERATURE.

So in theory, a 0w40, 5w40, 10w40, and 15w40 oils are all "40 weight" at engine operating temperature. Of course there are variances allowed so not all 10w40's are actually exactly the same, let alone a 0w40 and a 15w40. But you'd be wrong to assume that the 15w40 is necessarily the thicker one at engine operating temp.

So now for the number before the "w". Its a measure of how much the oil gets thicker as it cools down (actually a measure at a specific low temp, which I forget). All those Xw40 oils I mentioned start out the same thickness at engine temp, but as you cool them down, the 15w40 gets thicker than the 5w40, which in turn gets thicker than a 0w40. That's an oversimplification, because the "getting thicker" process isn't necessarily linear, but it gives you a rough idea. And room temperature is a no-man's land way between the hot and cold temps where the ratings matter, so it really doesn't mean much at all to observe an oil at room temp.

 

[Doog]

M1 0w-20:
Visc@100C: 8.7cSt
Visc@ 40C: 44.8cSt
MRV@ -40C: 9,200cP

M1 0w-40:
Visc@100C: 13.5cSt
Visc@ 40C: 75.0cSt
MRV@ -40C: 31,000cP

This means that both of these oils will pump in your car's engine if you decide to park on the dark side of the moon.

However, if you park here you will have issues:

What is the coldest place on Earth? It is a high ridge in Antarctica on the East Antarctic Plateau where temperatures in several hollows can dip below minus 133.6 degrees Fahrenheit (minus 92 degrees Celsius) on a clear winter night.

So as long as you don't park there or in the arctic circle you should be fine.

 

[BlackBeard]

Thanks very much everyone. What throws me off is if I had a straight 40 weight oil and a straight 20 weight oil side by side. It's just hard to believe that a 0-20 and 0-40 can both be the same in cold. But if I understand correctly it doesn't mean it looks and feels the same its just that it meets pour requirements. In my mind I am seeing a 0-40 in a cup looking like a watery 20 weight then heating up to be as heavy as a straight 40 weight oil and my mind finds that impossible so I know somethings askew

 

[kschachn]

One of the things askew is thinking the oil will thicken up when heated. Neither the 0W-20 nor the 0W-40 will be "watery" when cold, both will be thick. Having the oil thicken up when heated is impossible as you state.

Originally Posted By: BlackBeard
Thanks very much everyone. What throws me off is if I had a straight 40 weight oil and a straight 20 weight oil side by side. It's just hard to believe that a 0-20 and 0-40 can both be the same in cold. But if I understand correctly it doesn't mean it looks and feels the same its just that it meets pour requirements. In my mind I am seeing a 0-40 in a cup looking like a watery 20 weight then heating up to be as heavy as a straight 40 weight oil and my mind finds that impossible so I know somethings askew