Viscosity, viscosity, viscosity

Pennzoil motor oil
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Originally Posted by slickoil
At 100 degrees C, why is Mobil 1 5W30 more viscous than their 10W30?

See https://mobiloil.com/en/motor-oils/mobil-1/mobil-1

Higher viscosity index.

The 5w30's viscosity changes less with temperature, so it will tend to be thicker than the 10w30 at the hottest temps and thinner at the coldest temps.


Originally Posted by slickoil
Also, which is the more important value to look at: Viscosity at 40 degrees C, or Viscosity at 100 degrees C?

Both are important. 40 tells you more about how it runs when it's cold; 100 is more relevant to how your engine will run when everything's up to temp.


Originally Posted by slickoil
Regular vehicle is a Prius, and it doesn't show engine temp on the display.

Don't Priuses take xW-20?
 
Originally Posted by d00df00d
Originally Posted by slickoil
At 100 degrees C, why is Mobil 1 5W30 more viscous than their 10W30?

See https://mobiloil.com/en/motor-oils/mobil-1/mobil-1

Higher viscosity index.

The 5w30's viscosity changes less with temperature, so it will tend to be thicker than the 10w30 at the hottest temps and thinner at the coldest temps.


OK. I'm officially confused. I thought a 5W30 acts like a 5W when it is cold, and like a 30W when it is hot. So wouldn't that mean it changes viscosity more than a 10W30 due to temperature?


Originally Posted by d00df00d
Originally Posted by slickoil
Also, which is the more important value to look at: Viscosity at 40 degrees C, or Viscosity at 100 degrees C?

Both are important. 40 tells you more about how it runs when it's cold; 100 is more relevant to how your engine will run when everything's up to temp.


Thanks. 40 is still fairly hot (takes my truck over 2 minutes to get that hot, according to the guage). Why don't oil companies routinely post specs for less than 40 Celsius?

Originally Posted by d00df00d
Originally Posted by slickoil
Regular vehicle is a Prius, and it doesn't show engine temp on the display.

Don't Priuses take xW-20?


Ya, long story. It takes 0W20, but it's consuming oil, and several people recommended trying something thicker to see if that helps.
 
Originally Posted by slickoil
Originally Posted by d00df00d
Originally Posted by slickoil
At 100 degrees C, why is Mobil 1 5W30 more viscous than their 10W30?

See https://mobiloil.com/en/motor-oils/mobil-1/mobil-1

Higher viscosity index.

The 5w30's viscosity changes less with temperature, so it will tend to be thicker than the 10w30 at the hottest temps and thinner at the coldest temps.


OK. I'm officially confused. I thought a 5W30 acts like a 5W when it is cold, and like a 30W when it is hot. So wouldn't that mean it changes viscosity more than a 10W30 due to temperature?


Originally Posted by d00df00d
Originally Posted by slickoil
Also, which is the more important value to look at: Viscosity at 40 degrees C, or Viscosity at 100 degrees C?

Both are important. 40 tells you more about how it runs when it's cold; 100 is more relevant to how your engine will run when everything's up to temp.


Thanks. 40 is still fairly hot (takes my truck over 2 minutes to get that hot, according to the guage). Why don't oil companies routinely post specs for less than 40 Celsius?

Originally Posted by d00df00d
Originally Posted by slickoil
Regular vehicle is a Prius, and it doesn't show engine temp on the display.

Don't Priuses take xW-20?


Ya, long story. It takes 0W20, but it's consuming oil, and several people recommended trying something thicker to see if that helps.


The 5W-xx means it passes the CCS and MRV requirements at -30C and -35C for the 5W Winter rating. The number in front of the W isn't the same as the number that comes after it.
 
Originally Posted by slickoil
OK. I'm officially confused. I thought a 5W30 acts like a 5W when it is cold, and like a 30W when it is hot. So wouldn't that mean it changes viscosity more than a 10W30 due to temperature?

Good questions.

First thing: The W number is based on pumpability testing at very low (usually sub-freezing) temps. The bigger number is based mainly on kinematic viscosity (basically how easily the oil flows through a hole with gravity alone) at 100º C, plus a couple of other things. Different kinds of tests performed at very different temperatures. It's best not to think of them as comparable in any way. So, don't think of 5W as being "like a 5" at low temp; just think of it as 5W. Likewise, don't think of 30 as being "like a 30" at high temp; just think of it as 30.

Second thing: All oils, regardless of grade, are MUCH thicker at low temps than at high temps. The goal is to keep it from thickening too much at low temps and thinning out too much at high temps.

5w30 does behave "thinner" than 10w30 at low temps in the sense that it's more pumpable at those low temps where the W numbers are determined. But again, both oils are MUCH thicker when cold than when hot. The 5w30 just thickens less as you cool it down. The flip side of that is that it thins out less when you heat it up. Hence, 5w30 generally experiences less viscosity change than 10w30 (which experiences less than SAE 30). Etc.

Does that make sense?


Originally Posted by slickoil
Thanks. 40 is still fairly hot (takes my truck over 2 minutes to get that hot, according to the guage). Why don't oil companies routinely post specs for less than 40 Celsius?

40º C is ambient temp on a hot summer day. Hot for humans, but not for engines.

Oil companies often (but not always) post actual numbers from the pumpability tests that determine the W number. But even if they don't, the W number itself gives some info for temps far below 40º C.
 
Don't let the numbers play tricks on your mind. The truth is, most gasoline powered passenger cars would do just fine on 10w30; and I mean all of them.
 
Originally Posted by slickoil
. . .
Regular vehicle is a Prius, and it doesn't show engine temp on the display.

You just need to get yourself one of these:
[Linked Image]

It's a Scangauge-II. It's looking a bit sloppy since I haven't finalized its install just yet. You can display any four of dozens of parameters, the ones you see here are the four I set to monitor. Coolant temp is easy on the SG. Trans temp requires adding so-called custom "X-gauges". I'm not sure if there's an X-Gague for oil temp or not. Even if not, you can infer, roughly of course, the oil temps after the coolant temp has peaked and stabilized.

Note: not sure why the pic is displaying so small today. At any rate, I've got coolant temp, in deg F, showing in the lower right display.
 
Originally Posted by d00df00d

Good questions.

First thing: The W number is based on pumpability testing at very low (usually sub-freezing) temps. The bigger number is based mainly on kinematic viscosity (basically how easily the oil flows through a hole with gravity alone) at 100º C, plus a couple of other things. Different kinds of tests performed at very different temperatures. It's best not to think of them as comparable in any way. So, don't think of 5W as being "like a 5" at low temp; just think of it as 5W. Likewise, don't think of 30 as being "like a 30" at high temp; just think of it as 30.

Second thing: All oils, regardless of grade, are MUCH thicker at low temps than at high temps. The goal is to keep it from thickening too much at low temps and thinning out too much at high temps.

5w30 does behave "thinner" than 10w30 at low temps in the sense that it's more pumpable at those low temps where the W numbers are determined. But again, both oils are MUCH thicker when cold than when hot. The 5w30 just thickens less as you cool it down. The flip side of that is that it thins out less when you heat it up. Hence, 5w30 generally experiences less viscosity change than 10w30 (which experiences less than SAE 30). Etc.

Does that make sense?

Thank you for the excellent explanation. I read what you wrote several times, and things started making more sense.

Then I watched this: https://www.youtube.com/watch?v=Hb6CX_rWoIA

The YouTube video reinforces what I originally wrote: "I thought a 5W30 acts like a 5W when it is cold, and like a 30W when it is hot."

Is the video a bunch of bullarky?

You mentioned that a person can't think of 30 as being "like a 30" at high temp; just think of it as 30. Are you saying to think of xW-30 as an SAE30 oil, or not to do that?

It sounds like a 5W30 might be a good choice for what I'm trying to achieve. It'll be more viscous than 10W30 at high temps, which is good, and less viscous than 10W30 at low temps, which is also good.
 
Originally Posted by slickoil
Then I watched this: https://www.youtube.com/watch?v=Hb6CX_rWoIA

The YouTube video reinforces what I originally wrote: "I thought a 5W30 acts like a 5W when it is cold, and like a 30W when it is hot."

Is the video a bunch of bullarky?

You mentioned that a person can't think of 30 as being "like a 30" at high temp; just think of it as 30. Are you saying to think of xW-30 as an SAE30 oil, or not to do that?

As others have stated, the temperatures that the "5W" represents are extreme subzero. Not "cold', but "you're going to die out there" cold. What it does in between is variable. I use Mobil 1 0W-40. It's not thinner than regular Mobil 1 5w30 at any ambient temperature I'm likely to find in my part of California. But at an extreme cold temperature it will pump better than the 5w30.

The 30 represents being within a viscosity range at 100ºC. It doesn't necessarily represent the viscosity when it goes beyond that, which can happen in many engines. It's more or less regulated by the cooling system, but the oil is usually going to be hotter than the coolant for various reasons.

The whole SAE viscosity scale is probably outdated at this point, but we've had them so long that it would be difficult to use a different scale.

As far as your original question goes, there's nothing really all that unusual about it. 30 represents an acceptable range. Many times those are "typical" and there might be differences from manufacturing variations.
 
Originally Posted by slickoil
At 100 degrees C, why is Mobil 1 5W30 more viscous than their 10W30? ...





The second number is the oil grade, based on a viscosity range measured at 100 c. NOT WEIGHT . In the 10w30 example, 30 means nothing regarding the actual thickness of the oil, or weight of anything. It is a grade given to the oil if its measured viscosity at 100 c (212 f ) is between a certain range of thickness, in this case 9.3 Cst to 12.4 Cst. Any oil falling between this range is labelled a 30 grade. So you can, and do, have 30 grade oils that are thinner or thicker at the measured 100 c temperature. The oil manufacturer decides what exact viscosity their various 30 grade oils will actually be, but they will always fall between the allowable range.

So yes, different 30 grade oils can have different viscosities when measured at 100 c , like the Mobil 1 5w30 compared to Mobil 1 10w30.
 
Originally Posted by slickoil
Thank you for the excellent explanation. I read what you wrote several times, and things started making more sense.

cheers3.gif



Originally Posted by slickoil
Then I watched this: https://www.youtube.com/watch?v=Hb6CX_rWoIA

The YouTube video reinforces what I originally wrote: "I thought a 5W30 acts like a 5W when it is cold, and like a 30W when it is hot."

Is the video a bunch of bullarky?

It's solid info plus a couple of major misconceptions.

The biggest error is where he says the SAE grade would go up at low temps. The viscosity itself goes up at low temps, but the SAE grade does not because it's based on measurements at specific temps.

The part about 5W acting like an SAE 5 at cold temps isn't entirely without merit; I think that's how the W numbers were originally derived, though lubricant technology has moved on since then and a modern SAE 5 could have far better cold viscometrics than 5W. Hopefully someone corrects me if I'm wrong about that.

But either way, an SAE 5 is WAY thicker at those cold temps than an SAE 30 is at 100º C. That's key when it comes to your statement that you quoted above. And again, the W number and the big number are based on entirely different kinds of viscosity testing. So, it's still better to think about the W number and the big number as their own separate things, and it's still the case that a bigger "spread" between the numbers usually means less viscosity change with temperature, not more.
 
Originally Posted by d00df00d
slickoil said:
...
But either way, an SAE 5 is WAY thicker at those cold temps than an SAE 30 is at 100º C. That's key when it comes to your statement that you quoted above. And again, the W number and the big number are based on entirely different kinds of viscosity testing. So, it's still better to think about the W number and the big number as their own separate things, and it's still the case that a bigger "spread" between the numbers usually means less viscosity change with temperature, not more.


Thanks again. Your brain seems to work similar enough to mine that your posts are extra helpful. The second half of the last sentence above is the hardest part for me to wrap my head around, but here's what I came up with to try to understand (and remember ) it... tell me if I've got it right: A 5w30 oil will have to work in a larger range of conditions than a 10w30 oil; therefore its viscosity changes less overall; thus, in lower temperatures 5w30 will be less viscous than 10w30, and in higher temperatures the 5w30 will be more viscous than 10w30.
Click to expand...
 
Originally Posted by slickoil
Originally Posted by d00df00d
slickoil said:
...
But either way, an SAE 5 is WAY thicker at those cold temps than an SAE 30 is at 100º C. That's key when it comes to your statement that you quoted above. And again, the W number and the big number are based on entirely different kinds of viscosity testing. So, it's still better to think about the W number and the big number as their own separate things, and it's still the case that a bigger "spread" between the numbers usually means less viscosity change with temperature, not more.


Thanks again. Your brain seems to work similar enough to mine that your posts are extra helpful. The second half of the last sentence above is the hardest part for me to wrap my head around, but here's what I came up with to try to understand (and remember ) it... tell me if I've got it right: A 5w30 oil will have to work in a larger range of conditions than a 10w30 oil; therefore its viscosity changes less overall; thus, in lower temperatures 5w30 will be less viscous than 10w30, and in higher temperatures the 5w30 will be more viscous than 10w30.


No, the 10w30 could be a heavier lubricant overall and thus be heavier at 100C too.

I wrote up a long explanation for this a while back, let me see if I can dig it up.
Click to expand...
 
Originally Posted by OVERKILL
Originally Posted by slickoil
Originally Posted by d00df00d
slickoil said:
...
But either way, an SAE 5 is WAY thicker at those cold temps than an SAE 30 is at 100º C. That's key when it comes to your statement that you quoted above. And again, the W number and the big number are based on entirely different kinds of viscosity testing. So, it's still better to think about the W number and the big number as their own separate things, and it's still the case that a bigger "spread" between the numbers usually means less viscosity change with temperature, not more.


Thanks again. Your brain seems to work similar enough to mine that your posts are extra helpful. The second half of the last sentence above is the hardest part for me to wrap my head around, but here's what I came up with to try to understand (and remember ) it... tell me if I've got it right: A 5w30 oil will have to work in a larger range of conditions than a 10w30 oil; therefore its viscosity changes less overall; thus, in lower temperatures 5w30 will be less viscous than 10w30, and in higher temperatures the 5w30 will be more viscous than 10w30.


No, the 10w30 could be a heavier lubricant overall and thus be heavier at 100C too.

I wrote up a long explanation for this a while back, let me see if I can dig it up.


I think op is asking why:

Mobil 1 10Wx30 VT100 = 10.1
Mobil 1 05Wx30 VT100 = 11.0

Based on this particular case (spec), 5W has a higher cSt At 100°C.

iirc, for 5W (vs. 10W), a thicker base oil can be (or is) used to achieve the spread ... and not sure if that explains it or maybe I'm oversimplifying it.

Just noticed @d00df00d explained it in general.
Click to expand...
 
Last edited:
Originally Posted by slickoil
A 5w30 oil will have to work in a larger range of conditions than a 10w30 oil

It's more that a 5w30 is designed to be able to work down to lower temps. The range may or may not be higher.


Originally Posted by slickoil
therefore its viscosity changes less overall

Usually, yes.

Originally Posted by slickoil
thus, in lower temperatures 5w30 will be less viscous than 10w30

Generally true -- though technically it depends on the oils in question, the temps in question, and the measurements used. A 5w30 will have lower numbers than a 10w30 on pumpability tests at the absolute lowest temps, but it could still have higher kinematic viscosity at all other temps, including some that might still be considered "cold".


Originally Posted by slickoil
and in higher temperatures the 5w30 will be more viscous than 10w30.

Not always. Its viscosity will most likely decline less with heat, but that doesn't necessarily mean it'll end up being more viscous.

Let's say we have a 5w30 that is 65 cSt @ 40º C, and a 10w30 that is 75 cSt @ 40º C. Now let's say we heat them both up to 100º C, and the 5w30 drops to 10 cSt while the 10w30 drops to 11 cSt. The 10w30's viscosity dropped more, but it's still slightly thicker at 100º C.

Or it could be the other way around. The 5w30 could drop from 65 to 11 cSt while the 10w30 drops from 75 to 10.

It really depends on the oils in question.
 
Originally Posted by OilUzer
Originally Posted by OVERKILL
Originally Posted by slickoil
Originally Posted by d00df00d
slickoil said:
...
But either way, an SAE 5 is WAY thicker at those cold temps than an SAE 30 is at 100º C. That's key when it comes to your statement that you quoted above. And again, the W number and the big number are based on entirely different kinds of viscosity testing. So, it's still better to think about the W number and the big number as their own separate things, and it's still the case that a bigger "spread" between the numbers usually means less viscosity change with temperature, not more.


Thanks again. Your brain seems to work similar enough to mine that your posts are extra helpful. The second half of the last sentence above is the hardest part for me to wrap my head around, but here's what I came up with to try to understand (and remember ) it... tell me if I've got it right: A 5w30 oil will have to work in a larger range of conditions than a 10w30 oil; therefore its viscosity changes less overall; thus, in lower temperatures 5w30 will be less viscous than 10w30, and in higher temperatures the 5w30 will be more viscous than 10w30.


No, the 10w30 could be a heavier lubricant overall and thus be heavier at 100C too.

I wrote up a long explanation for this a while back, let me see if I can dig it up.


I think op is asking why:

Mobil 1 10Wx30 VT100 = 10.1
Mobil 1 05Wx30 VT100 = 11.0

Based on this particular case (spec), 5W has a higher cSt At 100°C.


It's not a spec, it's just how the two lubes were blended. Mobil 1 High Mileage 10w30 has a 100C visc of 12.1cSt. The Winter rating has nothing to do with the 100C visc, it's just what the blender (in this case Mobil) chose to blend it to.
Click to expand...
 
OVERKILL,
I think I added more after you quoted me. Please see my previous post again.

By spec I meant M1 published spec. or data sheet maybe a better choice.

How about 5Wx30 using thicker base oil than 10Wx30 causing higher kv100 theory. Any truth to that?
 
Last edited:
Btw, meant to type kv not sure how vt got in there! lol

Mobil 1 10Wx30 KV100 = 10.1
Mobil 1 05Wx30 KV100 = 11.0
 
Last edited:
Originally Posted by OilUzer
OVERKILL,
I think I added more after you quoted me. Please see my previous post again.

By spec I meant M1 published spec. or data sheet maybe a better choice.

How about 5Wx30 using thicker base oil than 10Wx30 causing higher vt100 theory. Any truth to that?


5w30 can use a thinner base (blend) or a thicker base depending on who is blending it. Typically however, the lower the W rating, the thinner the bases used because a heavier base isn't going to meet the W rating. The issue comes when there are ceilings on volatility, where you need to put in some expensive and heavier PAO to keep the Noack down, like with the Euro lubes.
 
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