Interpreting viscosity numbers

[Sierra048]

I have read about viscosity in the oil universiry section on BITOG. I'm just not getting it. Probably my age but it seemed a bit above me. I look at members posting UOAs and VOAs. When it comes to viscosity, what does one gleem from the numbers given, and what is the significance?

As an example, from a recent UOA posted in the UOA section, SUS viscosity @210°F = 44.8 and cSt viscosity @100°C = 5.65. Can someone help me understand what this is telling me? Would one interpret these values on a VOA differently since one is new and one used?

Let's say I was in the market for a thicker oil and I was looking at VOAs of different options. What would tell me which one was thicker than the others?

I'll apologize ahead of time if this little simplistic for some here on BITOG. It's just not for me. Thanks.

 

[The motor guy]

100 degrees celcius is the same as 210 farenheit. Actually I think it's 212. The CST number is the grade of the oil.

 

[RichardS]

As I understand it, the cSt would then tell you where on the scale an oil grade lands (thin vs thick within the specified grade), and in a UOA allows you to see how well that oil kept it's cSt going through the life of the oil change interval.

It's one of the things that you'd look at when deciding to extend or shorten an OCI for that engine with that oil going forward.

So, if you started with a 30 grade oil (9.30-12.4 at 100 cSt), and at 5k miles, the cSt was down to 8.0, then you know that your engine is beating that oil like it owes them money, and the oil has sheared down to a 20 grade.

Again, as far as I understand.

 

[Sierra048]

Originally Posted By: RichardS
As I understand it, the cSt would then tell you where on the scale an oil grade lands (thin vs thick within the specified grade), and in a UOA allows you to see how well that oil kept it's cSt going through the life of the oil change interval.

It's one of the things that you'd look at when deciding to extend or shorten an OCI for that engine with that oil going forward.

So, if you started with a 30 grade oil (9.30-12.4 at 100 cSt), and at 5k miles, the cSt was down to 8.0, then you know that your engine is beating that oil like it owes them money, and the oil has sheared down to a 20 grade.

Again, as far as I understand.



So, an oil weight/grade like 20, 30, 40 has a specified range as shown in your example above? Do all 30 weight oils, whether they are 0W, 5W, 10W etc.. fall into this range, with the thinner 30 weight closer to the 9.30 value and the thicker oils closer to the 12.4 value? Would a 40 weight oil be anything above the 12.4 value and a 20 weight be anything less than the 9.30 value? If so, I think I might be understanding this a little better. I appreciate your response.

 

[69GTX]

Originally Posted By: Sierra048
So, an oil weight/grade like 20, 30, 40 has a specified range as shown in your example above? Do all 30 weight oils, whether they are 0W, 5W, 10W etc.. fall into this range, with the thinner 30 weight closer to the 9.30 value and the thicker oils closer to the 12.4 value? Would a 40 weight oil be anything above the 12.4 value and a 20 weight be anything less than the 9.30 value? If so, I think I might be understanding this a little better. I appreciate your response.


You basically have it now. Though it might be hard to find quality 30 grades as thin as 9.30. The thinner 30 grades are usually in the 9.8-10.0 range, iirc. And if your car is specced for a 30 grade oil, it would be preferable to stay as close to the new viscosity rating as possible.

I use a M1 0w-40 FS oil for my 5w-30 specced car. It's a thinner 40 grade that starts out at around 12.8 cSt. Within a couple thousand miles it would probably shear down by a point or more, and close to where M1 5w-30 starts out (11.1 cSt at 100c).

 

[RichardS]

^ what he said, you've got the basics. Each grade (20, 30, 40, 50, 60) has a viscosity range to meet for it to qualify. They can be thick or thin within the grade, but still be a 30. SO you could pick a 30 with a VOA cSt closer to the 12.4, and it would be a thicker 30 oil.

The w has little/no bearing on the 100c cSt of the oil grade. It's msotly just cold pumping performance. Unless you live somewhere that it gets - degrees, you can mostly just do whatever xw-30 suits your fancy. It starts to get hairier when you're dealing with an engine that is hard on oil, and causes it to shear quickly to a lower grade.

 

[Sierra048]

Thanks everyone. I feel a little more confident in my understanding of it now.

 

[RichardS]

No sweat. I'm glad I was able to help. Happy motoring.

 

[Garak]

Originally Posted By: Sierra048
Let's say I was in the market for a thicker oil and I was looking at VOAs of different options. What would tell me which one was thicker than the others?

I wouldn't do it that way. I'd pay attention to HTHS. You can get some ideas, depending upon grade and specification met.

If you're looking at an ordinary ILSAC 5w-20 or 0w-20 and are only wanting to run a 20 grade, most are more similar than they are different. If you want thicker within the grade, you're stuck with something like Red Line, which doesn't meet ILSAC standards, for good and for bad.

If you're using an ordinary 5w-30 SN/GF-5, if you want thicker within that grade, you look at an HDEO, or an A3/B4 or a C3 oil, if you want to stay within the 5w-30 grade but be thicker at operating temperatures. The viscosity difference between one 5w-30 SN/GF-5 and another at operating temperatures is hair splitting and not worth the effort to determine. Note that moving from a 5w-30 SN/GF-5 to a 10w-30 SN/GF-5, while we're at it, isn't giving you a thicker oil, either, at least not at operating temperature.

 

[Sierra048]

Thanks Garak. When looking at an oil's PDS, and all they have listed is the kinematic viscocity at 40°C and 100°C, where would one get the HTHS value? And, do I understand that minus an HTHS value, these values will give one an idea as to its thickness?

 

[Garak]

Some have it, some don't; perhaps most don't, unfortunately. HTHS is far, far more important at determining operational viscosity. But, you can usually make a fairly good estimate of HTHS, at least with mainstream oils meeting ordinary specifications. With boutiques and race oils, it's harder to guess, but they're more likely to publish the figure in the first place.

Basically, if you're looking at an ILSAC 30, you've got an HTHS of 3.1 +/- 0.1, almost without exception. If you're looking at a 20 grade, your minimum HTHS is 2.6, and you're not going to see an ILSAC 20 leapfrog that by any significant amount, at least not into the 30 grade HTHS minimum. Red Line's 20 grades do, but they're not ILSAC approved.

 

[Sierra048]

Again Garak, much appreciated. I had added another paragraph to my last post but it didn't get posted. No doubt something I did wrong.
I'll try again.

I'm considering trying the Delo 400 XLE 10w30 semi-syn for our Nissan Frontier. It is a grade suitable for the Frontier. The PDS for this newer CK4/SN shows KV @: 40°C = 81, 100°C = 11.9. How would this rate as far as thickness, assuming it can be determined by these numbers? Or would additional info be required.

We live in the N. Georgia mountains, several of our access roads to our home are pretty steep, and I thought a little thicker oil might be beneficial with our summer heat.

 

[RichardS]

Garak,
How does the HTHS (high temp/high sheer, right?) affect the operating thickness of the oil? It determines how robust the oil is to resisting viscosity loss during operation, yes?

Thanks

 

[Sierra048]

Just did some searching and found that any CK rated oil has to have a minimum HTHS of 3.5. I read that a minimum HTHS for a 30 weight was 2.9. Could one assume that a CK4 30 weight oil is at least 21% thicker at a minimum or am I looking at this wrong?

 

[RichardS]

I think because it's not API rated, the requirements are different? Also, I'm not sure what the max HTHS is for a 30, and if they cross over from API.

 

[Jetronic]

There is no MAX HTHS, only a minimum.

 

[Jetronic]

Originally Posted By: Sierra048
Just did some searching and found that any CK rated oil has to have a minimum HTHS of 3.5. I read that a minimum HTHS for a 30 weight was 2.9. Could one assume that a CK4 30 weight oil is at least 21% thicker at a minimum or am I looking at this wrong?


You're looking at it wrong.

CK rated oils have a HTHS minimum of 3.5 Cst, yes. ACEA A3/B4 and C3 or C4 oils aswell.

For just API rated oils, the minimum is 2.9, but they can be anywhere upwards of that limit. So you could find an oil without diesel rating that has a higher than 3.5cP HTHS aswell. But those won't be ILSAC rated.

 

[Sierra048]

Originally Posted By: Jetronic
Originally Posted By: Sierra048
Just did some searching and found that any CK rated oil has to have a minimum HTHS of 3.5. I read that a minimum HTHS for a 30 weight was 2.9. Could one assume that a CK4 30 weight oil is at least 21% thicker at a minimum or am I looking at this wrong?


You're looking at it wrong.

CK rated oils have a HTHS minimum of 3.5 Cst, yes. ACEA A3/B4 and C3 or C4 oils aswell.

For just API rated oils, the minimum is 2.9, but they can be anywhere upwards of that limit. So you could find an oil without diesel rating that has a higher than 3.5cP HTHS aswell. But those won't be ILSAC rated.


OK. Thanks for the info.

 

[Garak]

Originally Posted By: Sierra048
I'm considering trying the Delo 400 XLE 10w30 semi-syn for our Nissan Frontier. It is a grade suitable for the Frontier. The PDS for this newer CK4/SN shows KV @: 40°C = 81, 100°C = 11.9. How would this rate as far as thickness, assuming it can be determined by these numbers? Or would additional info be required.

You'll probably be at or a bit over 3.5 in HTHS, which is fine. I don't know if you have warranty left, but with Nissans, you can use any 5w-30 SN, not just SN/GF-5. So, you could use something like Shell Rotella T5 Multi-Vehicle 5w-30 or Mobil Delvac 1 LE 5w-30, and still be technically satisfying warranty requirements, all the while having your HTHS up at 3.5 or higher. But, the Delo would do a fine job, I'm sure. It will certainly be thicker at operating temperatures than your run of the mill 5w-30 SN/GF-5 you'd find on the shelf.

The KV numbers are not of a lot of use to us here, other than determining the actual SAE grade, really.

RichardS: Here is a fairly readable definition of HTHS from Lubrizol.

Jetronic answered the rest of the questions very nicely.

 

[Sierra048]

Great information. Thanks to all.