If all oil is too thick when cold...

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665
Location
WA
What's the point of oil grades like 5w-30 or 10w-30 or 15w-40? Why not just use 0w-30/0w-20/0w-40 when possible? I've read and searched but could never find a definitive answer
 
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13,255
Location
North Carolina
I don't know if there is a lot of difference in a 0w30 and a 5w 30 above freezing. I've always thought that it would be more useful to have cst numbers for 0c as well as 100c, verses 40c and 100c.
 

CT8

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15,392
Location
Idaho
Originally Posted By: SnowDrifter
What's the point of oil grades like 5w-30 or 10w-30 or 15w-40? Why not just use 0w-30/0w-20/0w-40 when possible? I've read and searched but could never find a definitive answer
Not everything on the internet is actually fact that really matters.
 
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2,191
Location
VA
0w-xx reminds me of Subaru's 'Partial Zero Emissions Vehicle.' You can't have a partial 0. I don't dig into numbers for flow rates and such, but i'm just not going to run a 0w oil in anything unless the manufacturer state to use a 0w oil.
 
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43,676
Location
'Stralia
All lubricants are a compromise, and the compromise comes in different areas. e.g. * a 15W40 will generally have a higher HTHS, and be more shear stable (temporary and permanent shear) than a 0W40. * a 0W40 starting at -25C is a cakewalk, versus the 15W40 that will be struggling to pump at those temperatures. * 0W40 will not thicken as much below operating temperature as the 15W, and return slightly better average fuel economy. * 15W40 will likely be less volatile. * And the 0W40 is undoubtedly more expensive than nearly every 15W40. Similar arguments for all the other grades.
 
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2,744
Location
San Antonio, TX
And even Texas - such as the Panhandle and Davis Mountains . . . My last truck (a 5.9L or 360 V8) spec'd either 10W-30 or 5W-30 based on expected ambient temperature during the OCI (both minimum & maximum). In Ohio, I ran 5W-30 about half the year and 10W-30 about half the year. In Southeast Louisiana, I ran 10W-30 year-round. This is a robust engine design that had been manufactured for decades with decades of experience on its service life. If the manufacturer had seen an advantage at the time of its production to switch to some 0W-XX oil, including CAFE effects, I'm confident they would have spec'd things differently. Others may not be so confident. I sold it earlier this year with 154,000 miles on it running strong and zero lubrication issues.
 

Kestas

Staff member
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13,983
Location
The Motor City
As I understand it, vaporization starts to become a significant factor for 0W oils. That's why most of these oils are synthetic. Also, going from 10W to 5W "buys" you about 16 degrees F to get the same viscosity. I'm not sure how much more temperature you'll buy going to 0W.
 
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262
Location
Central Florida
Originally Posted By: Kestas
As I understand it, vaporization starts to become a significant factor for 0W oils. That's why most of these oils are synthetic. Also, going from 10W to 5W "buys" you about 16 degrees F to get the same viscosity. I'm not sure how much more temperature you'll buy going to 0W.
All 0w oils are synthetic. Viscosity Index of conventional base stocks are not high enough to produce a 0w-xx oil. 0w-xx oils will flow faster and provide less resistance upon cold start in all climates. Those that live in really cold climates like the upper mid-west and Canada will benefit most. In Florida, not so much.
 
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43,676
Location
'Stralia
Originally Posted By: BrianC
0w-xx oils will flow faster and provide less resistance upon cold start in all climates.
How do they flow faster...? The positive displacement oil pump ensures that the same volume of oil is shifted per revolution, regardless of viscosity... Until you get down to the point that the 0W, 5W, 10W start to play a part in terms of oil not actually being pumpable, or starving the supply side of the pump.
 
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8,051
Location
Michigan
Because not all oil is "too thick" when cold. It's just much thicker than it needs to be. The API defines "too thick when cold" as 60,000 cP at their defined temperature setpoints for the various W-grades in the Cold Pumpability test.
 
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262
Location
Central Florida
Originally Posted By: Shannow
Originally Posted By: BrianC
0w-xx oils will flow faster and provide less resistance upon cold start in all climates.
How do they flow faster...? The positive displacement oil pump ensures that the same volume of oil is shifted per revolution, regardless of viscosity... Until you get down to the point that the 0W, 5W, 10W start to play a part in terms of oil not actually being pumpable, or starving the supply side of the pump.
Well, "faster" might not be the best word. But less resistance and parasitic drag might better describe it.
 
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3,561
Location
Central Iowa
Or do what I do... I use oil pan heaters on all my vehicles and equipment. 15w40 flows, at cold startup, like a warm summer's day. And that is even at -30F which I experience a few times in the upper midwest winters.
 
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6,388
Location
Washington St.
Quote:
If all oil is too thick when cold...
To thick for what? Racing? Running a cold engine at highway speeds? Well, yes. To just get you going easy until your engine is warm? No.
Quote:
0w-xx oils will flow faster and provide less resistance upon cold start in all climates. How do they flow faster...? The positive displacement oil pump ensures that the same volume of oil is shifted per revolution, regardless of viscosity...
Well...yes, the pump is positive displacement, but it also has a pressure control valve. When the set point is reached, oil is dumped back to the sump to prevent excess pressure. With thick oil, less will be pumped through the engine. Does "less" mean "not enough?" No, not for an easy warm up. Recall the three jobs of oil--lubricate, carry away heat, carry away particles. During the warm up there is no excess heat, and not enough junk to worry about. So, why not use all 0W-x oils? Cost, mainly. If the 0W-x oils can be made without excessive viscosity index improvers (which do not lubricate, they just take up space in the oil), then they probably work fine.
 
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10,146
Location
Burlington, Ontario, Canada
Originally Posted By: Ken2
[quote] So, why not use all 0W-x oils? Cost, mainly. If the 0W-x oils can be made without excessive viscosity index improvers (which do not lubricate, they just take up space in the oil), then they probably work fine.
Where did you get the idea that polymer VIIs don't lubricate? It is very slippery stuff that does an excellent job of lubricating. The only negative with VIIs is shear stability when lower quality VIIs are used. The highest VI oils, predominately the OEM 0W-20s, actually use less VIIs than many of their much lower VI counterparts. The only reason 0W oils aren't used across the board is cost.
 
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