Understanding Viscosity and HTHS

[JustN89]

After pondering viscosity and HTHS and my vehicles, I had a couple of questions that I thought I would ask on here.

My cars spec 5W-20, 5w30 and 10w30, and I've been running 5w30 in both for the majority of the time I've owned them. They're both port injected, naturally aspirated, and seem relatively easy on oil. Anyways, I started looking at different 5w30 oils and got to wondering something.

One of the oils I looked at was Motul 8100 X-Clean EFE 5w30. This is an API certified oil, so I picked out another API certified oil to compare it to. This version of Motul would be perfectly acceptable in both of my vehicles because, as the owner's manual states, any API certified 5w30 is fine.

Here's the stats on Motul 8100 X-Clean EFE, and a few highlighted below:

Visc. @ 40C: 70.1
Visc. @ 100C: 12.1
HTHS: 3.5

Now, as I stated, this oil would be perfectly fine witth regards to the warranty, as it meets the stated requirements. However, lets compare it to an oil that would be outside the requirements of my warranty.

Mobil 1 0W-40, a well regarded oil on here, would be an oil that could technically void my warranty if I ran it as it's not a recommended viscosity. However, here's the stats for this oil. Compare it to the Motul 8100 5w30.

Visc. @ 40C: 70.8
Visc. @ 100C: 12.1
HTHS: 3.6

Now, I'm sure I'm missing something obvious and I know Visc. @ 40/100 isn't everything, so please excuse my ignorance on the subject, but why would the Motul be a 5w30 and the Mobil 1 be a 0W-40? I'm also assuming that, since the obvious thick 5w30 would be fine in my engine (per the OM), the Mobil 1 0W-40 would also be perfectly fine (though outside the recommended viscosity)? I thought I remembered reading that a 5w30 couldn't have an HTHS above 3.5, but I could be wrong. Is the .1 mPa.s make that much difference?

Thanks!


Note: Please leave brand out of the discussion as much as possible. I know that any 5w30 is fine (IBTQSUD5w30BestValueAtWalmart$19.50), I just had some questions about how two similar oils could have a different viscosity and one be within my warranty and one outside.

 

[CT8]

The 2 oils are very different. The Motul is low ash the M1 High ash. Both are good oils but different.Go with the MFG recommendations ..

 

[jbutch]

Viscosity and HTHS can be similar, yet the additives can be very different and therefore not be recommended for that reason.

12.1 @ 100c is a very thick 30 weight oil and a very thin 40 weight at the same time.

 

[d00df00d]

Originally Posted by JustN89
Mobil 1 0W-40, a well regarded oil on here, would be an oil that could technically void my warranty if I ran it as it's not a recommended viscosity. However, here's the stats for this oil. Compare it to the Motul 8100 5w30.

Visc. @ 40C: 70.8
Visc. @ 100C: 12.1
HTHS: 3.6

Now, I'm sure I'm missing something obvious and I know Visc. @ 40/100 isn't everything, so please excuse my ignorance on the subject, but why would the Motul be a 5w30 and the Mobil 1 be a 0W-40? I'm also assuming that, since the obvious thick 5w30 would be fine in my engine (per the OM), the Mobil 1 0W-40 would also be perfectly fine (though outside the recommended viscosity)? I thought I remembered reading that a 5w30 couldn't have an HTHS above 3.5, but I could be wrong. Is the .1 mPa.s make that much difference?

Looks like the spec sheet for Mobil 1 0W-40 FS says 12.9 cSt @ 100º C, not 12.1. So, between that and the HTHS values, you're looking at two oils that straddle the line between xW-30 and xW-40: the Motul at or just below, and the Mobil just above.

Beyond that, though, the formulations are going to be different. They both meet some very tough specs, but X-Clean EFE is a low SAPS engine oil and FS 0W-40 isn't.

I wouldn't expect the differences in viscosity to matter as long as the application was appropriate for either oil. But if the application calls for specs that only one of them carries, I wouldn't run the other.

EFE looks like incredible stuff. MB 229.52 is no joke. If my application could take that oil, and if cost weren't a consideration, I wouldn't look twice at Mobil 1 FS 0W-40.

 

[JustN89]

Originally Posted by d00df00d
Originally Posted by JustN89
Mobil 1 0W-40, a well regarded oil on here, would be an oil that could technically void my warranty if I ran it as it's not a recommended viscosity. However, here's the stats for this oil. Compare it to the Motul 8100 5w30.

Visc. @ 40C: 70.8
Visc. @ 100C: 12.1
HTHS: 3.6

Now, I'm sure I'm missing something obvious and I know Visc. @ 40/100 isn't everything, so please excuse my ignorance on the subject, but why would the Motul be a 5w30 and the Mobil 1 be a 0W-40? I'm also assuming that, since the obvious thick 5w30 would be fine in my engine (per the OM), the Mobil 1 0W-40 would also be perfectly fine (though outside the recommended viscosity)? I thought I remembered reading that a 5w30 couldn't have an HTHS above 3.5, but I could be wrong. Is the .1 mPa.s make that much difference?

Looks like the spec sheet for Mobil 1 0W-40 FS says 12.9 cSt @ 100º C, not 12.1. So, between that and the HTHS values, you're looking at two oils that straddle the line between xW-30 and xW-40: the Motul at or just below, and the Mobil just above.

Beyond that, though, the formulations are going to be different. They both meet some very tough specs, but X-Clean EFE is a low SAPS engine oil and FS 0W-40 isn't.

In an application that could take either oil, I wouldn't expect significant differences. But I wouldn't run either of those oils in an application that didn't call for its specs/approvals.

You're right, I mis-typed that. I understand that they are different formulations, sorry for the confusion. I was strictly talking about viscosities, but it looks like I just found an oil at the very top of the XW-30 and an oil at the very bottom of the XW-40.

Thanks everyone for the input.

 

[RDY4WAR]

I tend to view a higher HTHS for the same KV100 as an indicator of superior base oils.

 

[OVERKILL]

Originally Posted by RDY4WAR
I tend to view a higher HTHS for the same KV100 as an indicator of superior base oils.


Yes, and likely less VII content.

 

[oil_film_movies]

This confusion is why German engine specs say "use 229.52" for example, to take most of the XwXX debate out. The spec itself is sufficient to choose an oil. (Although, it's true if you want better severe cold performance, you do choose a 0wXX within your spec.) Some engine makers do combine the old fashioned XwXX grouping with a spec, like "use Xw30 & dexos1 oil" for example.

Originally Posted by JustN89
One of the oils I looked at was Motul 8100 X-Clean EFE 5w30. This is an API certified oil, so I picked out another API certified oil to compare it to. This version of Motul would be perfectly acceptable in both of my vehicles because, as the owner's manual states, any API certified 5w30 is fine.
Maybe not "Owner's Manual Legal". Some OMs say an oil must be SN and GF-5, & to get GF-5 it's HTHS must be low enough to pass the Sequence VID fuel economy tests. That usually puts HTHS at 3.2 at the most. More HTHS makes MPG go down, hydrodynamic drag.

Originally Posted by JustN89
I thought I remembered reading that a 5w30 couldn't have an HTHS above 3.5, but I could be wrong. Is the .1 mPa.s make that much difference?
Minimum oil film thickness (MOFT) is pretty close to proportional to HTHS, so 0.1/3.5 = 1/35 = about 3% difference in MOFT, not really that much. As MOFT shrinks, more surface metal-to-metal happens inside your engine, so you'd better have really good zddp, moly, tungsten, titanium, polymer esters, etc. variety of stuff fighting on the surface to keep wear and friction down more.

A 5w30 is allowed to have HTHS greater than 3.5 (Redline 5w30 has HTHS 3.7) by definition. The official definition to define an XwXX is (note HTHS is expressed as the minimum value only):

 

[Snagglefoot]

I happened to have a pic of the Motul product. Not that common in the States. It's actually Dexos 2 approved. Enjoy.

 

[53' Stude]

Originally Posted by Snagglefoot
I happened to have a pic of the Motul product. Not that common in the States. It's actually Dexos 2 approved. Enjoy.



That's the DEXOS 2 for Diesel engines not DEXOS 1 GEN2 for gas applications

 

[Snagglefoot]

Correct and Dexos 2 was developed by GM for use in Petrol and Diesel engines.

 

[Gokhan]

Originally Posted by JustN89
After pondering viscosity and HTHS and my vehicles, I had a couple of questions that I thought I would ask on here.

My cars spec 5W-20, 5w30 and 10w30, and I've been running 5w30 in both for the majority of the time I've owned them. They're both port injected, naturally aspirated, and seem relatively easy on oil. Anyways, I started looking at different 5w30 oils and got to wondering something.

One of the oils I looked at was Motul 8100 X-Clean EFE 5w30. This is an API certified oil, so I picked out another API certified oil to compare it to. This version of Motul would be perfectly acceptable in both of my vehicles because, as the owner's manual states, any API certified 5w30 is fine.

Here's the stats on Motul 8100 X-Clean EFE, and a few highlighted below:

Visc. @ 40C: 70.1
Visc. @ 100C: 12.1
HTHS: 3.5

Now, as I stated, this oil would be perfectly fine witth regards to the warranty, as it meets the stated requirements. However, lets compare it to an oil that would be outside the requirements of my warranty.

Mobil 1 0W-40, a well regarded oil on here, would be an oil that could technically void my warranty if I ran it as it's not a recommended viscosity. However, here's the stats for this oil. Compare it to the Motul 8100 5w30.

Visc. @ 40C: 70.8
Visc. @ 100C: 12.1
HTHS: 3.6

Now, I'm sure I'm missing something obvious and I know Visc. @ 40/100 isn't everything, so please excuse my ignorance on the subject, but why would the Motul be a 5w30 and the Mobil 1 be a 0W-40? I'm also assuming that, since the obvious thick 5w30 would be fine in my engine (per the OM), the Mobil 1 0W-40 would also be perfectly fine (though outside the recommended viscosity)? I thought I remembered reading that a 5w30 couldn't have an HTHS above 3.5, but I could be wrong. Is the .1 mPa.s make that much difference?

Thanks!


Note: Please leave brand out of the discussion as much as possible. I know that any 5w30 is fine (IBTQSUD5w30BestValueAtWalmart$19.50), I just had some questions about how two similar oils could have a different viscosity and one be within my warranty and one outside.

Mobil 1 FS 0W-40 KV100 = 12.9 cSt, not 12.1 cSt.

Running a quick calculation:

Mobil 1 FS 0W-40 VII content: 7.7%
Motul 8100 X-clean EFE 5w30 VII content: 5.8%

Mobil 1 FS 0W-40 base-oil viscosity: 2.1 cP
Motul 8100 X-clean EFE 5w30 base-oil viscosity: 2.2 cP

Therefore, Motul uses a slightly thicker base oil to start with and has 3/4 of the VII Mobil 1 has. These are both good things and Motul wins in both the base-oil viscosity (thicker the better) and VII content (less the better).

Motul also has the modern mid-SAPS C3 and dexos2 specs, which makes it compatible with more cars in the modern day in contrast to the Mobil 1 FS's full-SAPS A3/B4 spec, which was popular with the Euro cars of the past but it is getting less common in the latest cars because a lower phosphorus and ash content is preferred for aftermarket systems and direct injection and better additive packages and base oils make up for the lower detergent content of the C3/dexos 2.

 

[Gokhan]

Originally Posted by Gokhan
Running a quick calculation:

Mobil 1 Full Synthetic 0w40 VII content: 7.7%
Motul 8100 X-clean EFE 5w30 VII content: 5.8%

Mobil 1 Full Synthetic 0w40 base-oil viscosity: 2.1 cP
Motul 8100 X-clean EFE 5w30 base-oil viscosity: 2.2 cP

Therefore, Motul uses a slightly thicker base oil to start with and has 3/4 of the VII M1 has. These are both good things and Motul wins in both the base-oil viscosity (thicker the better) and VII content (less the better).

I could also calculate the base-oil viscosity index from the VII content:

Mobil 1 Full Synthetic 0w40 base-oil viscosity index: 134
Motul 8100 X-clean EFE 5w30 base-oil viscosity index: 130

Therefore, M1 has a higher-quality base oil than the Motul (higher the base-oil viscosity index, the better) and it wins in that respect.

However, the Motul wins hands down in the VII content, as it has only 3/4 the VII M1 has (less the better).

 

[d00df00d]

Gokhan, you know better. Stop this.

 

[oil_film_movies]

Originally Posted by 53' Stude
Originally Posted by Snagglefoot
I happened to have a pic of the Motul product. Not that common in the States. It's actually Dexos 2 approved. Enjoy.
That's the DEXOS 2 for Diesel engines not DEXOS 1 GEN2 for gas applications

The Motul says "SN" on it, so its good for gasoline engines too. Its also true that GM has endorsed a dexos2 for their gasoline Corvettes as well, here in the states.

 

[Gokhan]

Originally Posted by d00df00d
Gokhan, you know better. Stop this.

Stop what? I calculated the viscosity-index improver (VII) content and from that the viscosity and viscosity index (VI) of the base oil.

The original poster was asking how the viscosity worked out and I think this has answered this question.

 

[JAG]

Quote
Minimum oil film thickness (MOFT) is pretty close to proportional to HTHS, so 0.1/3.5 = 1/35 = about 3% difference in MOFT, not really that much.

I've read multiple papers that said it is proportional to the SQUARE ROOT of the high shear rate viscosity at whatever the temperature of the oil is.

 

[Gokhan]

Originally Posted by JAG
I've read multiple papers that said it is proportional to the SQUARE ROOT of the high shear rate viscosity at whatever the temperature of the oil is.

That sounds correct:

This is the dependence of the bearing wear on HTHSV and MOFT, the latter being proportional to the square root of the HTHSV:

Contrary to what one might naïvely expect, the bearing wear actually increases with the increasing HTHSV and increasing MOFT. My guess for the reason for this phenomenon is that the increasing HTHSV increases the bearing temperature, which in turn increases the bearing corrosion and wear. Nevertheless, there is a minimum HTHSV that is needed below which catastrophic bearing failure occurs. As Jim Allen once said, the optimal oil viscosity grade is the thinnest oil that is thick enough (or something to that effect -- I can't remember his exact words).

https://www.jstor.org/stable/44472105

Effect of oil rheology on journal-bearing performance: Part 4 -- Bearing durability and oil-film thickness
Published September 1, 1989 by SAE International in United States
Event: 1989 SAE International Fall Fuels and Lubricants Meeting and Exhibition
T. W. Bates -- Shell Research Ltd.,Thornton Research Centre, Chester, England
G. B. Toft -- Shell Research Ltd.,Thornton Research Centre, Chester, England

(You need to create a free account to read the article.)

My take: Find out what the required HTHSV is for your car and don't go any higher. Then, find an oil that with the least viscosity-index improver (VII) content that meets this HTHSV spec. This will result in the highest fuel economy, smoothest- and cleanest-running engine, and probably the least engine wear as well.

 

[Garak]

Originally Posted by JustN89
My cars spec 5W-20, 5w30 and 10w30, and I've been running 5w30 in both for the majority of the time I've owned them. They're both port injected, naturally aspirated, and seem relatively easy on oil. Anyways, I started looking at different 5w30 oils and got to wondering something.

You mention warranty concerns, so I thought I should bring up something in the regard. And no, it's not about whether using the wrong viscosity will or won't void your warranty, either. I'll leave that one alone.

Note that when a manual specifies one or more viscosities, they usually specify something else along with viscosity, such as API, ILSAC, ACEA, or proprietary specifications. You mentioned API, but most will specify something else. My G37 specifies only 5w30 in API (SM was current then). ILSAC was only optional. A dexos2/SN 5w30 or a CK-4/SN 5w30 perfectly meet my [expired] warranty requirements, but that's not the case for everyone.

When it comes to your italicized question, that's been creating debate here for a very long time. The difference in HTHS between the 5w30 CK-4 I'm running and an A3/B4 or C3 0w-40 is much closer than the difference between my 5w30 and an ILSAC 5w30.

 

[d00df00d]

Originally Posted by Gokhan
Originally Posted by d00df00d
Gokhan, you know better. Stop this.

Stop what? I calculated the viscosity-index improver (VII) content and from that the viscosity and viscosity index (VI) of the base oil.

No, you didn't. You ran the numbers through a series of equations you made up -- equations with zero experimental validation and mostly negative feedback from the few real experts who deigned to comment -- and then you posted the results as though they were completely legit.

If you tried this in a professional or academic setting, any reputable company or institution would laugh you out of the room, and you know it.

There are bloody good reasons for that, and you know it.

So much of what you do here is valuable. So much of what you've posted in this thread and others is on-point and insightful. You can do better. You do it all the time. It's some of the most valuable content on the site. And then you do stuff like this, trying to claim a veneer of legitimacy for something you know hasn't earned it, and it undermines not only your credibility but the whole forum's. And again, you know it.

What you do here matters. You have a much higher standard to uphold than almost everyone else here has. You know how to uphold it. Please make the choice to do so.