With a 0w-30 oil, I assume that the 30 is the actual weight of the oil but at freezing temps it will act as a zero weight oil. So, does this oil become thinner at colder temps? As the temps become higher through driving and during the summer months, then this same oil's viscosity would raise to at least the 30w or higher depending on the oil used. Correct? For instance the GC 0w-30 oil will actually become almost a 40w oil according to tests but at freezing temps it acts as a 0w oil? Viscosity numbers are confusing to me!
Understanding Viscosity Numbers
- Thread starter yankees1
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Actually, the best phrase is "a 0W is less thick at very cold, sub-zero temperatures, than a 5W or a 10W engine oil".
Just keep in mind, what I'm sure you already know, "Oil gets thicker as the temperature gets colder".
The viscosity of GC 0W-30 follows this basic progression:
Full 212F Operating Temp - 12.1 cSt
Room 72F Temps - 150 cSt
Freezing 32F Temps - 545 cSt
Zero 0F Temps - About 2000 cSt
And on down to the 0W rating at -30C where the viscosity is several thousand centistokes.*
* Sorry, I don't have the time to look up & convert the GC cold crank rating from centipoise to centistokes.
Just keep in mind, what I'm sure you already know, "Oil gets thicker as the temperature gets colder".
The viscosity of GC 0W-30 follows this basic progression:
Full 212F Operating Temp - 12.1 cSt
Room 72F Temps - 150 cSt
Freezing 32F Temps - 545 cSt
Zero 0F Temps - About 2000 cSt
And on down to the 0W rating at -30C where the viscosity is several thousand centistokes.*
* Sorry, I don't have the time to look up & convert the GC cold crank rating from centipoise to centistokes.
Or how about something even simpler . . .
At cold temperatures it gets thicker, but not as thick as an old conventional straight 30 weight would . . . more like a 0 weight.
At hot temperatures, it gets thinner, but not as thin as an old conventional straight 0 weight would . . . more like a 30 weight.
Blue99 had a more technically correct explanation . . . but the SAE number started way back when conventional oil changed viscosity a lot with temperatures, and you had to change oil seasonally. A simple 10, 20 or 30 rating was easy for people to grasp. The multi-weight numbers were created to give the user some point of reference of how one oil could replace a range oils they used before. To try to understand it any other way gets confusing . . . c'mon, a zero weight oil seems like it should have no viscosity whatsoever, right?
At cold temperatures it gets thicker, but not as thick as an old conventional straight 30 weight would . . . more like a 0 weight.
At hot temperatures, it gets thinner, but not as thin as an old conventional straight 0 weight would . . . more like a 30 weight.
Blue99 had a more technically correct explanation . . . but the SAE number started way back when conventional oil changed viscosity a lot with temperatures, and you had to change oil seasonally. A simple 10, 20 or 30 rating was easy for people to grasp. The multi-weight numbers were created to give the user some point of reference of how one oil could replace a range oils they used before. To try to understand it any other way gets confusing . . . c'mon, a zero weight oil seems like it should have no viscosity whatsoever, right?
Keep in mind that a 0w-20 vs 0w-30 the 0w-20 will have much better cold starting specifications. It is in the way the specifications are allowed for each weight. 0w-40 oils cold starting specifications are not as good as 5w-30 specifications. So the 0 does not mean what one would think it means. Maybe some day it will but for now the best specs for cold starting are in the 0w-20 weights.
At 100°C (212°F) a 5w30 oil has the viscosity of a 30-weight oil. At -30°F, or thereabouts, a 5w30 oil has the viscosity of a 5-weight oil. The reason I say "thereabouts" is that as far as I know the lower "winter" viscosity number is referenced to various temperatures, depending on the manufacturer.
Completely wrong.
Actually only half wrong, the second half.
Reread my post, please. I don't believe I said or implied that the first viscosity number was "comparable" to the second.
I did, however, state, correctly or incorrectly, that the "W" number, in this case "5", may or may not be referenced to -30°F depending on the oil's manufacturer. In the case of GC, I understand the "0" to be referenced to -30°F.
I did, however, state, correctly or incorrectly, that the "W" number, in this case "5", may or may not be referenced to -30°F depending on the oil's manufacturer. In the case of GC, I understand the "0" to be referenced to -30°F.
Maybe this SAE J300 viscosity chart will help a bit:
Before CCS Specs, SAE w-rating would actually mean the oil would have the visc *that a SAE 10 would have* at freezing, although it was a 30 at operating temp.
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