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.
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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.