Difference between SM & SN

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I did a search, and found a few discussions about SM & SN oils. But, I can't really find a solid answer. What's the difference? What makes a SN a SN? And a SM a SM? What does one have that the other doesn't? Simple to understand answers are greatly appreciated! Thanks
 
Seems as though almost all SN rated oils contain at least a small amount of molybdenum, maybe some boron.

There are probably other things that've changed that we can't see in a VOA or a UOA, though.
 
Then there are some SN oils that have "taken out" or "reduced" the amount of Moly from the SM rated oil. Case in point....take a look at Havoline in SN compared to SM...Where is the Moly? It's all gone in the SN version of Havoline! Take a look again at Valvoline MaxLife, HM, synthetic blend in SM and compare it to the SN. Where is the Moly in the SN? The SM had a nice big dose of Moly and now it's missing from the SN, per VOA results.

Now take a look at PYB SN and SM.....they added a nice healthy dose of Moly to SN, PYB from the previous version of SM.

You also hear all this talk about "Organic" additives, that do not show up on UOA's or VOA's, in the SN oils to replace the metallic add packs in the SM versions. But what are these "Organic" add packs? Seems like it is a trade secret that even the Labs are unaware of in motor oils.

Originally Posted By: JRed
Seems as though almost all SN rated oils contain at least a small amount of molybdenum, maybe some boron.

There are probably other things that've changed that we can't see in a VOA or a UOA, though.
 
Mongo, there still is a pretty nice dose of moly in Maxlife SN. The whole thing is, the additives that the major companies are using are more efficient. Less is needed to achieve the same or better result while protecting emissions systems.
 
Mobil has also switched to a balanced Ca/Mg pack. This has been taken both ways. Some think it's a sign of a cheaper product, some say the extra Mg helps it with TBN retention.

UOA's will tell.
 
Dare I ask? Which is "better"? SM or SN???

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An oil that meets the SN minimum specs is better than an oil that meets the SM minimum specs. That does not mean that any oil rated SN will be better than any oil rated SM.
 
Thanks Dan. Just went to the GF-5 website. Lots of info there. here is a excerpt.

Quote:
Improved phosphorous retention (ZDP) to enable emission system durability while maintaining engine protection

Increased levels of organic/inorganic Friction Modifiers to meet improved fuel economy and fuel economy retention

Enhanced emulsion and rust protection for Flex Fuel Vehicle specifically those that run on ethanol based fuel (E85)

Greater seal compatibility to help ensure seal longevity and prevent oil leakage in older vehicles, as demonstrated by a new seal test specifically developed for GF-5
 
So if you have a very modern, low friction engine, GF-5 is what you want.

It could be.....The engine clearances might be very small in the new low friction engines, thus the need for GF-5 oils.

So thinner is much better for very modern engines with tight clearances. Less metallic additives, like Moly, help the flow of oil to reach into these narrow passageways for lubrication. The more metallic additives....the thicker the oil.... unless it is all VI.
 
Metallic additives have very little (almost nothing) to do with the thickness of the oil. The length of hydrocarbons in the oil base stock is what determines the thickness of the oil. VII's (viscosity index improvers) and PPD's (pour point depressants) assist in low temperature flowing and pumpability of the oil. VII's can also smooth out the viscosity graphed as a function of temperature.

I have no idea what you are talking about with "modern low friction engines". Modern engines are built with greater precision and tighter tolerances but that has little to do with friction. They can use lighter oil because oil technology and engine technology has improved to the point where film strength is maintained with less viscous oil. That's why people with older cars sometimes use thicker oil, because the increased tolerances of the cylinders makes it so that the thin oil cannot maintain film strength. The only connection between modern engines and friction is that a less viscous oil will provide less resistance which equals better fuel economy.

Viscosity of oil also has nothing to do with it being SM or SN, GF-4 or GF-5.
 
Originally Posted By: cmf
Metallic additives have very little (almost nothing) to do with the thickness of the oil. The length of hydrocarbons in the oil base stock is what determines the thickness of the oil. VII's (viscosity index improvers) and PPD's (pour point depressants) assist in low temperature flowing and pumpability of the oil. VII's can also smooth out the viscosity graphed as a function of temperature.

I have no idea what you are talking about with "modern low friction engines". Modern engines are built with greater precision and tighter tolerances but that has little to do with friction. They can use lighter oil because oil technology and engine technology has improved to the point where film strength is maintained with less viscous oil. That's why people with older cars sometimes use thicker oil, because the increased tolerances of the cylinders makes it so that the thin oil cannot maintain film strength. The only connection between modern engines and friction is that a less viscous oil will provide less resistance which equals better fuel economy.

Viscosity of oil also has nothing to do with it being SM or SN, GF-4 or GF-5.


We have thinner coated ring packs, coated pistons, roller cams and rockers, coated cam followers, reduced friction cam chains all in production engines. I would say friction has been reduced in modern engines.
 
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Here's the difference from API's website .... SN CURRENT Introduced in October 2010 for 2011 and older vehicles, designed to provide improved high temperature
deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource
Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger
protection, emission control system compatibility, and protection of engines operating on ethanol-containing
fuels up to E85.
SM CURRENT For 2010 and older automotive engines more info.... http://www.api.org/certifications/engineoil/pubs/upload/MOTOR_OIL_GUIDE_2010_120210-2.pdf
 
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I have oils in my stash that are API-SM rated, but meet or exceed the requirements for GF-5.

Castrol Edge, Gold Jug, manufactured in January, 2011.
Strauss Auto Parts, Full synthetic API-SM, GF-4
1, 5 quart jug, Pennzoil Ultra, API-SM, GF-4

All of these oils are API-SM rated but meet or exceed the requirements for GF-5.
 
Not surprisingly the SN GF-5 standard is superior to the the SM GF-4 standard. But that doesn't mean an SN oil is necessarily better than the previous SM version in all categories.

For example, it seems to be harder to make a high VI 20 and 30 wt SN oil; the SN versions almost universally have lower VIs; sometimes markedly. The difficulty appears to be emission related deposit control.
 
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