Buick, there are 0w-XX oils, even 0w-30, that have lower NOACKS and higher HT/HS viscosities then any conventional SM/GF-4 oils and many "synthetic" passenger car oils. Look at some of the HDEO 0w-30s. It's all in how an oil is made. Most passenger car oils are blended on the thinner side.
The NOACKS and HT/HS viscosities of synthetic 0w-xx are usually equal to or better then conventional 5w30 and 10w-30 oils, so you kind of get the best of both worlds with a 0w-xx oil - equal or usually better high temperature viscosity/oxidation control, and better flow at cold starting temps.
What am I missing, because I'm sure you're going to point it out!
Nothing. You're right as long as it's a high quality 0w oil compared to an average 5w or 10w... Or a syn vs dino as you said. But take two nearly identical high quality oils, Redline for instance and compare their 0w-20 vs 5w-20. Significant reduction in HTHS.
Originally Posted By: CATERHAM
Firstly welcome back BuickGN.
I don't agree with your comparison of RL's 0W-20 and 5W-20.
Their 5W-20 is for all intents and purposes a 30wt oil so it's not an apples to apples comparison.
Thank you.
I'm comparing a 20wt to a 20wt. The 5w-20 is on the heavy side but why put it at an unfair disadvantage and compare it to a 30wt? It is a 20wt.
But if we have to, the 5w-20 is thinner than the 0w-30 at 40c and 100c yet it has a higher HTHS. The viscosities aren't going to cross on the cold end until you're colder than most of us start our engines at. It sounds like a win-win.
Originally Posted By: CATERHAM
The more viscous the oil the higher the HTHS vis. It's not a good thing or a bad thing it's just what it is.
The 0w-30 is thicker than the 5w-20 at 100c yet it has a lower HTHS.
The 0w-20 is not even worth discussing in an HTHS battle.
Originally Posted By: CATERHAM
HTHS viscosity is a valuable spec' not so much because it is taken at 150C but rather how the viscosity is measured; under pressure, which is more representative on how oil behaves in an engine vs kinematic viscosity. It should come as no surprise to anyone who has an oil pressure gauge equipped car and is familiar with RL 5X-XX and heavier oils that they behave like a grade heavier than their SAE grade because they are heavier even at normal operating temp's. RL actually advises customers of this characteristic with their oils suggesting that one can frequently drop a grade when switching to RL.
They suggest you can drop a grade and take advantage of the better flow due to the very high HTHS. Other than the slightly thick 5w-20, the others are right in grade.
Originally Posted By: CATERHAM
When comparing oils purportally of the same grade it's best to be aware of any significant difference in their HTHS vis to keep the comparison valid.
Regarding NOACK percentages, while lower is obviously better, since all SM oils must have a volitility under 15% the issue is largely mute. Case in point would be PP 0W-20 which has a NOACK of 14%. Seemngly high, but this shear stable oil has been tested enough by BITOG members with no measureable oil comsumption.
There have been some on here with some oil consumption. Could also be the mechanical condition of the engine, who knows. But the point is, even if it's not measurable it can still show up in combustion chamber deposits as the engine ages. And if something is going away, even though it's just a little, something has to change with what's left behind.
,,well then why do they exist?
