Relevance of MRV spec

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The_Eric

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I've been searching a bit for my "winter" oil. I'd like to run a 40 grade as it's right in the middle of the Hyundai spec and was thinking Mobil 0w-40 or RLI 5w-40 if I can find it for a reasonable price.

My question is, using the Widman graph, it appears that Mobil 1 0w-40 is a pretty good choice for the cold, if you look at it's MRV spec, it doesn't look so good. So what gives?

The two 5w30's are simply in there for comparison. If it matters any, the Kendall is their blend with the liquid titanium. Could someone help me understand the MRV spec?

WidmanGraph3.jpg
 
1. The Widman graph isn't very accurate at very low temps.

2. You're looking at kinematic viscosity. MRV is a measure of pumpability.
 
Agreed.
I'd go on to say the MRV spec' is an accurate
a measure of viscosity at very cold temps.

For the OP, I'd say you certainly don't require a 40wt oil for winter use and would suggest M1's 0W-30.
 
Quote:
So what gives?


The (almost universal) assumption that all that is of a given "W" is/are created/perform equal(ly).

A 40 grade is ALWAYS heavier at ALL temps than a 30 grade ..is heavier than a 20 grade ..in all sensible terms. Always. It will react within certain limits at extremely cold temps.

The MRV will give you a decent comparison between two "0w's". You'll note that a 0w30 tends to have a lower MRV than a 0w-40 and a higher MRV than a 0w-20.

Makes sense to me, even if I can't really grasp all the fundamentals of non-Newtonian physics.


If you think about it, would there be any assumption that a 40 grade would get some "free ride" up to operating temperature? That, if compared, a 0w20 vs. 0w30 vs. 0w-40 ..all appeared the same from -35F ...all the way up to 100C/212F?

No. That would be unrealistic. It works the same way in the other direction if you're thinking of "sensible flow".
 
Originally Posted By: Gary Allan
A 40 grade is ALWAYS heavier at ALL temps than a 30 grade ..is heavier than a 20 grade ..in all sensible terms. Always. It will react within certain limits at extremely cold temps.

...All else equal (e.g. base stocks, measurement method, shear conditions).
 
Originally Posted By: d00df00d
1. The Widman graph isn't very accurate at very low temps.

2. You're looking at kinematic viscosity. MRV is a measure of pumpability.

Originally Posted By: CATERHAM
Agreed.
I'd go on to say the MRV spec' is an accurate
a measure of viscosity at very cold temps.

For the OP, I'd say you certainly don't require a 40wt oil for winter use and would suggest M1's 0W-30.


Ah, yes, I see it now. I remembered someone talking once about an oils cold temperature pumpability. This is obviously what they were saying.


Originally Posted By: Gary Allan
Quote:
So what gives?


The (almost universal) assumption that all that is of a given "W" is/are created/perform equal(ly).

A 40 grade is ALWAYS heavier at ALL temps than a 30 grade ..is heavier than a 20 grade ..in all sensible terms. Always. It will react within certain limits at extremely cold temps.

The MRV will give you a decent comparison between two "0w's". You'll note that a 0w30 tends to have a lower MRV than a 0w-40 and a higher MRV than a 0w-20.

Makes sense to me, even if I can't really grasp all the fundamentals of non-Newtonian physics.


If you think about it, would there be any assumption that a 40 grade would get some "free ride" up to operating temperature? That, if compared, a 0w20 vs. 0w30 vs. 0w-40 ..all appeared the same from -35F ...all the way up to 100C/212F?

No. That would be unrealistic. It works the same way in the other direction if you're thinking of "sensible flow".


Gary, my replies will be in order of your paragraphs.

-I knew this to be untrue, but not why.

-Why is this? Could you better explain it?

-Thank you for the pointer

-Makes two of us

-I honestly figured that's what additives did. Evidently not.


While I'm here, I have a couple of other questions...

1) I remember asking here once, why not all oils that were a 5w (for example) had the same or similar 40* spec... Gary Allan said that they were a standard and gave me a PDF of how they were measured. Now for the life of me, I can't find it. Does anyone have that PDF, or have the ability to convey the principle?

2) Why do different oil companies give the MRV spec at different temperatures? Also, is it fair to say that the MRV spec would be linear through the temps?

Example: @ -20* its 6000, @ -30* 7000 and @ -40* 8000

Or is it more of a curve like this?

@ -20* 6000, @ -30 6500, @ -40* 8000
 
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The MRV for each W grade is done at a different temperature - ie, for any 0w-xx oil, it's tested at -40C, compared to 5w-xx at -35c. Therefore it has a lower MRV viscosity by definition of the SAE oil grading system.
 
Originally Posted By: Drew99GT
The MRV for each W grade is done at a different temperature - ie, for any 0w-xx oil, it's tested at -40C, compared to 5w-xx at -35c. Therefore it has a lower MRV viscosity by definition of the SAE oil grading system.


Wow Drew, you answered my question before I finished typing it! You're goooooooood!
 
So what is it about the Widman graph that is inaccurate?

Also, how do the MRV and CCS figures compare?
 
The widman graph is accurate - it shows the measured kinematic viscosity of oil. MRV and CCS numbers are 2 entirely different things then kinematic viscosity. They are measured differently using different tests.
 
Originally Posted By: d00df00d
Originally Posted By: Gary Allan
A 40 grade is ALWAYS heavier at ALL temps than a 30 grade ..is heavier than a 20 grade ..in all sensible terms. Always. It will react within certain limits at extremely cold temps.

...All else equal (e.g. base stocks, measurement method, shear conditions).


Can you name a 12.5+ cst fluid that's lighter than a 9.3cSt fluid (expand as you sensibly can without me filling in the obvious details) at any temp ..assuming that you're comparing "w" to "w" or monograde to monograde ..conventional to conventional or synthetic to synthetic? I doubt that you can find a fluid out there with narrow vs. broad VI to "cross over" on the divergence.

We're obviously talking kinetic visc here.
 
Originally Posted By: Gary Allan
Can you name a 12.5+ cst fluid that's lighter than a 9.3cSt fluid (expand as you sensibly can without me filling in the obvious details) at any temp ..assuming that you're comparing "w" to "w" or monograde to monograde conventional to conventional or synthetic to synthetic?

...

We're obviously talking kinetic visc here.

Exactly my point. Without those qualifications, it's not true that a higher grade oil is "ALWAYS" heavier than a lower one.

You did add "in all sensible terms" in your post; just saying you should emphasize and qualify that.

...which seems to have been done. So it's all good now.
thumbsup2.gif
 
Originally Posted By: The_Eric
So what is it about the Widman graph that is inaccurate?

I'm not sure of the details, but my understanding is that at super-low temps, oils don't always behave the way the graph's calculations predict.


Originally Posted By: The_Eric
Also, how do the MRV and CCS figures compare?

From here: https://bobistheoilguy.com/forums/posts/1836257/

Originally Posted By: XS650
The viscosity of many liquids, oil included, vary with how much pressure is used and/or how fast the test is run.

The old low temperature viscosity test was basically a glorified pour test and didn't tell you much about how the oil would behave in a cold engine while it is cranking, or how it would pump.

There are two SAE J300 tests to determine low temperature viscosity. One is to determine the pumpability of the oil.The test method is designed to determine if an oil pump can pick the oil up and pump it. Pumpability is done 5 degrees colder than the cold cranking test, you don't want your engine to start if the pump can't supply oil.

The cold cranking test is done in a device that approximate how the oil gets sheared while an engine is cranking. There is a more force involved. If you want to look further, this looks like a good start...http://en.wikipedia.org/wiki/Cold-Cranking_Simulator
 
So my next question is this: Is there a way to compare the MRV/CCS of a 0w and say a 5w? It kind of goes back to my previous question of are the MRV/CCS numbers a straight line or a curve (viewed on a graph) from temp to temp...
 
In general, you can double the number of the higher w oil. For instance, say a 5w30 has a CCS of 4,000 cP @ -30C, and a MRV spec of 15,000 cP @ -35C. To compare it to a 0w oil, which tests CCS @ -35C and MRV @ -40C, double the numbers. It's not totally accurate, but in the ball park.

What you'll find though is, it's a futile excersize as oils are engineered to fit in each SAE W grade, so most 5w30s will never pass the CCS test for a 0w by definition. Most grades, especially synthetic, will pass the next lower W grade MRV test though.
 
Okay so using the 0w30 M1 (17100 MRV) as an example and comparing that to say, Ultra 5w30 (13000 MRV), I'd just double the Ultra MRV (26000) and compare to M1 (17100).

Looking at it that way, it appears that M1 will pump considerably easier than Ultra?

Out of curiousity, why the need to (approximately) double the higher W number's MRV spec?
 
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