Less likely to lose oil: 5w20 with noack around 8% or 5w30 with noack around 14%

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I am confused which would be more likely to lose oil. A thicker oil with a high noack or a thinner oil with a low noack...

I have a GDI that loses quite a lot of oil between changes so this is something I've been thinking about
 
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Originally Posted by Whammo
I have a GDI that loses quite a lot of oil between changes...

Loses oil, as in leaks, or burns it ?
 
The following study found out that in a typical healthy engine, oil volatility (as measured by Noack) contributes to around 1/3 of the total oil consumption. So, 1/3 * (14% - 8%) / 8% = 25%, which means a 25% increase in oil consumption in a healthy engine.

I am guessing the dominant oil-consumption mechanism in your case is not evaporation but transport though.

The contribution of different oil-consumption sources (PDF link)
The contribution of different oil-consumption sources to total oil consumption in a spark-ignition engine
Ertan Yılmaz, Tian Tian, Victor W. Wong, and John B. Heywood
Sloan Automotive Laboratory, Massachusetts Institute of Technology
 
Well it just had the gasket replaced and still is losing some oil somewhere (we don't see any smoke either). There is no longer any oil on the ground where I park.
 
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girlfriends 13 malibu was taking a qt on a thou at 63 thou + thats with synthetic 5-40 + a trade was the cure! no smoke no drips. 5-20 dexos was the worse then 10-30 doing better for a while then 5-40 until a trade all decent fake synthetic group III oils. never tried redline in it but its ester base oils are said to be best for DI + very low noacks. being in a cooler climate a 5-30 real synthetic in winter + a 10-30 real synthetic in summer + redlines ester oil flows great in extreme cold + resists burnoff in high heat
 
Originally Posted by Whammo
I am confused which would be more likely to lose oil. A thicker oil with a high noack or a thinner oil with a low noack...

I have a GDI that loses quite a lot of oil between changes so this is something I've been thinking about



What kind of Kia, year model and how many miles? Do you get less oil loss in the Minnesota Winters with added fuel dilution?
 
How much oil are you using, a qrt every how many miles?

Noack can be tricked by the use of vii, HTHS cannot as it is a hotter test, or should I say less likely to be tricked. Get both numbers if you can, even .1 hths more will withstand more burn. I'd be looking at the heaviest sn+ 5w30 I could find, bonus for high moly. It is very likely that the heaviest cSt will follow suit, but yes if you can good too see the triangle cst, noack, and hths.
 
Originally Posted by burla
How much oil are you using, a qrt every how many miles?

Noack can be tricked by the use of vii, HTHS cannot as it is a hotter test, or should I say less likely to be tricked. Get both numbers if you can, even .1 hths more will withstand more burn. I'd be looking at the heaviest sn+ 5w30 I could find, bonus for high moly. It is very likely that the heaviest cSt will follow suit, but yes if you can good too see the triangle cst, noack, and hths.


?

Noack volatility test is much hotter than the HTHS test:
https://www.mt.com/ca/en/home/supportive_content/matchar_apps/MatChar_UC252.html

Quote
The Noack test to quantitatively determine the evaporation loss of oils under standard conditions was introduced many years ago. For example, the DIN 51581 [3] test method measures the evaporation loss over a period of one hour at 250 °C under vacuum (2 mbar).

The ASTM D6375 standard thermogravimetric test method was developed [5] to combine the advantages of the gas chromatographic method [6] with the realistic conditions of the traditional Noack test. The method is quicker and more reliable than both and can be performed with less sample material.

According to the ASTM D6375 method, a sample is heated rapidly in a crucible to 249 °C and held isothermally for 30 min at this temperature during which time the TGA curve is recorded.


HTHS visc is measured at 150C, 100C cooler.

Volatility hinges heavily on the base oil. Lighter bases are more volatile, and while VII content will have an effect on it, overall, one must use heavier bases to achieve lower volatility.

On the other hand, HTHS visc is easily pumped up using VII, which is why high visc spread oils like 5w-50 have high HTHS, yet shear like mad. If you look at the SRT 0w-40, it has a much higher Noack than the "Euro" 0w-40's like Ravenol (Noack 8.5%) because it uses, IIRC, a 4cSt GTL base oil.
 
Noack is per volume, not thickness related. 8% is 8% and 14% is 14% regardless of how thick it is.

5w30 is thicker than 5w20 but it doesn't mean it use a thicker base oil. It could be a thinner base oil with some temperature sensitive thickener in there (aka VI Improver), or a blend of many types of base oil that're very different in viscosity, while the 5w20 is more homogeneous. The thinner part of the base oil blend will evaporate first, so that part of 5w30 is thinner than the thinnest part of the 5w20, or have more of this thinner base oil portion in 5w30, and therefore more will evaporate.

This is why the wider the spread the higher the noack in general, and 5w30 is worse than 5w20 in noack.
 
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Originally Posted by PandaBear
Noack is per volume, not thickness related. 8% is 8% and 14% is 14% regardless of how thick it is.

5w30 is thicker than 5w20 but it doesn't mean it use a thicker base oil. It could be a thinner base oil with some temperature sensitive thickener in there (aka VI Improver), or a blend of many types of base oil that're very different in viscosity, while the 5w20 is more homogeneous. The thinner part of the base oil blend will evaporate first, so that part of 5w30 is thinner than the thinnest part of the 5w20, or have more of this thinner base oil portion in 5w30, and therefore more will evaporate.

This is why the wider the spread the higher the noack in general, and 5w30 is worse than 5w20 in noack.


It technically is "thickness" related, but it's how heavy the bases being used are. For example, a 4cSt base will be more volatile (have a higher Noack) than a 6cSt base oil of the same type.

An oil with a heavier base oil blend will have a harder time, with VII, meeting both the cold temperature performance qualifications (W-rating) while also hitting its intended hot target. Ergo, typically thinner bases are used to blend wider spreads. You use a lighter base, so that the W-rating can be achieved, and more VII, to hit your 100C visc target.

Of course base oil selection (type) plays a role here as well. You can have a 5w-20 that's blended on the cheap with much higher Noack and VII treat rate than a 5w-30 that's blended with higher quality bases. And those bases may in fact be heavier as well, if they are bases with inherently better cold temperature performance like PAO.
 
Originally Posted by Gokhan
The following study found out that in a typical healthy engine, oil volatility (as measured by Noack) contributes to around 1/3 of the total oil consumption. So, 1/3 * (14% - 8%) / 8% = 25%, which means a 25% increase in oil consumption in a healthy engine.

I am guessing the dominant oil-consumption mechanism in your case is not evaporation but transport though.

The contribution of different oil-consumption sources (PDF link)
The contribution of different oil-consumption sources to total oil consumption in a spark-ignition engine
Ertan Yılmaz, Tian Tian, Victor W. Wong, and John B. Heywood
Sloan Automotive Laboratory, Massachusetts Institute of Technology



Question for you:

ultimately the difference between the Noacks is %6 ...
Are you saying if an oil has a noack of %x, typical oil consumption for that car is %3*x per the study?
Lets for the sake of argument agree with the study which i need to read first but have a hard time to picture the correlation ie the 3 times factor ...
So if that's the case, overall oil consumption is projected to be %18 (3 * %6) more.
How did you come up with %25?

I maybe missing something and can't connect the dots. Can you please explain?
 
I am losing a quart every 2000mi at the minimum. The reason I ask this strange question is because it seems 5w20 oils usually have a much lower noack than 5w30 ones. I use conventional or blend because the OCI is short enough that I would be wasting good synthetic. I have heard that a thicker oil would help consumption over a thinner oil but have also heard that a low noack helps as well.
 
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