Pour point vs. W rating....questions...

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Hey guys,

I have learned a ton here over the years without starting to many threads, but I can't seem to find an answer to my question. A friend brought up this subject yesterday and I was not able to add too much to the discussion..

Anyway, why/how is there such a variance in the pour point with a given weight of oil? Is there a minimum pour point that must be met for each weight? (Is this the same as the coldest temp the weight is rated to?) He is interested in finding the 'best' oil for cold starts in very cold weather (we are in very far Upstate NY). Is the pour point the most important spec when determining this?

To me, it seems like the pour point and viscosity can be related, but not always (meaning that a thinner oil typically has a lower pour point, but not always?)

Hope this makes sense.

-Travis
 
Originally Posted By: TurboTravis
Hey guys,

I have learned a ton here over the years without starting to many threads, but I can't seem to find an answer to my question. A friend brought up this subject yesterday and I was not able to add too much to the discussion..

Anyway, why/how is there such a variance in the pour point with a given weight of oil? Is there a minimum pour point that must be met for each weight? (Is this the same as the coldest temp the weight is rated to?) He is interested in finding the 'best' oil for cold starts in very cold weather (we are in very far Upstate NY). Is the pour point the most important spec when determining this?

To me, it seems like the pour point and viscosity can be related, but not always (meaning that a thinner oil typically has a lower pour point, but not always?)

Hope this makes sense.

-Travis


The reason that Pour Point was abandoned for determining an oil's cold temperature performance was due to its unreliability. It was so bad that they came up with two entirely new tests: CCS and MRV, to properly gauge it.

An oil with a ton of PAO in it will have a wickedly low pour point because PAO has no wax in it that will crystallize at low temperatures. However, it still thickens as temperature drops. PPD's and VII treat in a lighter base oil blend that doesn't consist of PAO can still outperform it at the temperatures the tests are performed at, the wildcard is if you are using an oil below that range; below the temperature acceptable for the grade.
 
Look at the CCS. 5W-30 is good for a -30 C (-22 F) start. The all time low for Syracuse, New York was -13 F on New Year's Day. Not a problem for a 5W-xx oil. If you'd like to have an even more dependable start 0W-xx would make it a non-event. I'm speaking from experience. Used to live in Edmonton, Alberta, Canada.

SF
 
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Originally Posted By: OVERKILL
Originally Posted By: TurboTravis
Hey guys,

I have learned a ton here over the years without starting to many threads, but I can't seem to find an answer to my question. A friend brought up this subject yesterday and I was not able to add too much to the discussion..

Anyway, why/how is there such a variance in the pour point with a given weight of oil? Is there a minimum pour point that must be met for each weight? (Is this the same as the coldest temp the weight is rated to?) He is interested in finding the 'best' oil for cold starts in very cold weather (we are in very far Upstate NY). Is the pour point the most important spec when determining this?

To me, it seems like the pour point and viscosity can be related, but not always (meaning that a thinner oil typically has a lower pour point, but not always?)

Hope this makes sense.

-Travis


The reason that Pour Point was abandoned for determining an oil's cold temperature performance was due to its unreliability. It was so bad that they came up with two entirely new tests: CCS and MRV, to properly gauge it.

An oil with a ton of PAO in it will have a wickedly low pour point because PAO has no wax in it that will crystallize at low temperatures. However, it still thickens as temperature drops. PPD's and VII treat in a lighter base oil blend that doesn't consist of PAO can still outperform it at the temperatures the tests are performed at, the wildcard is if you are using an oil below that range; below the temperature acceptable for the grade.



This.

No one seems to understand and too many walk away thinking an oil with a lower pour point is a better product or is made up of more PAO. As I've said before anyone can just pour a bunch of VII and it appears to look quote good on paper vs a product with substantially more PAO content in it.
 
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It's not that simple though. You can't just pour ppd and VII into an ordinary base oil and expect to hit CCS and MRV numbers as well as KV100. Not to mention the secondary impact on API and ACEA bench and engine tests.
 
Originally Posted By: TurboTravis
Anyway, why/how is there such a variance in the pour point with a given weight of oil? Is there a minimum pour point that must be met for each weight? (Is this the same as the coldest temp the weight is rated to?) He is interested in finding the 'best' oil for cold starts in very cold weather (we are in very far Upstate NY). Is the pour point the most important spec when determining this?


Travis,
the pour point (or the more modern "Youtube Bottle Glug") test inherently feel like they are applicable to low temperature starting, and for a long, long time, the "W" rating was based on it, or factors like it.

Testing identified that the brookfield viscosity was a better correlation to how long it took things to get to the top end in test engines.


And later yet, they found that there were specific cooling rates, that occurred one winter causing engine carnage encouraged the wax crystals to grow regardless of the actual temperature extreme that was reached (so neither pour point nor straight viscosity applied).

The MRV test has the "perfect storm" of cooling rates, designed to show any weakness in wax formation, with the viscosity limit of 60,000mPa-s (600P), and importantly not to have a "yield" stress, or "jello" like phase.

This test is about whether when the pump starts pumping, the oil is capable of
a) being sucked up the feed tube (OVERKILL's analogy); or
b) "falling" back in around the pickup tube to replace the oil that has been pumped into the engine.

(CCS is about how well the engine cranks, and therefore starts).

So in order
* pick a "W grade" that suits...assuming that he wants 0W.
* pick one with a smaller MRV (for example GM has a limit of 40,000MPa-s on dexos oils, 2/3 of the absolute limit.
* if you want to flavour it with Pour point, do so, but it's last on the list.
 
Originally Posted By: Shannow
And later yet, they found that there were specific cooling rates, that occurred one winter causing engine carnage encouraged the wax crystals to grow regardless of the actual temperature extreme that was reached (so neither pour point nor straight viscosity applied).

The MRV test has the "perfect storm" of cooling rates, designed to show any weakness in wax formation, with the viscosity limit of 60,000mPa-s (600P), and importantly not to have a "yield" stress, or "jello" like phase.

This test is about whether when the pump starts pumping, the oil is capable of
a) being sucked up the feed tube (OVERKILL's analogy); or
b) "falling" back in around the pickup tube to replace the oil that has been pumped into the engine.

(CCS is about how well the engine cranks, and therefore starts).


Exactly. The pour point test is not part of motor oil specifications because it fails to predict an oil's low temperature performance in an engine due to its low shear rates and an inappropriate cooling rate.

The CCS test is a higher shear test that correlates well to an oil's ability to be pumped.

The MRV test uses a slow cooling rate to promote wax crystallization and correlates well to an oil's ability to flow back into the pick-up tube cavity.

Tom NJ/VA
 
Originally Posted By: Snagglefoot
Look at the CCS. 5W-30 is good for a -30 C (-22 F) start. The all time low for Syracuse, New York was -13 F on New Year's Day. Not a problem for a 5W-xx oil. If you'd like to have an even more dependable start 0W-xx would make it a non-event. I'm speaking from experience. Used to live in Edmonton, Alberta, Canada.

SF


Just for the record
smile.gif
-13f was the coldest new year's day on record...not coldest day ever. At one time -26f was the record low in Syracuse, not sure if it has gone lower than that or not.

Northern NY (OP's location) is a whole different story. I saw -34 in my brief travels up there this year. I live a little southeast from Syracuse where it's down right balmy compared to the north country. Somebody in Quebec keeps leaving the door open, allowing the Arctic air to drift straight down into northern NY.
 
Originally Posted By: Tom NJ
The CCS test is a higher shear test that correlates well to an oil's ability to be pumped.


Tom, the CCS is specifically related to the cranking speed, and the ability of the engine to start.

The flow velocities in the galleries are still low shear.
 
Yes, if the engine won't start, it won't pump, but if it won't start it doesn't need to pump.

CCS is about cranking speed and starting...not pumping.

CCS
https://www.researchgate.net/publication...nd_Fuel_Economy
the relationship between viscosity and engine performance

MRV
http://www.tandfonline.com/doi/abs/10.1080/10402000601105540

The MRV ensures that every revolution the Positive Displacement pump makes it stays filled and delivering.

Because the engine needs to turn to deliver oil mechanically, does not make CCS any determinant of ability to pump oil...other than getting the engine running of course.
 
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