Originally Posted By: Gokhan
Recently there has been concerns regarding premature timing-chair wear, which resulted in people using thicker oils. Many people think that when they use a 0W-40, they are putting in a thick oil because it's "40-grade" when it's at normal operating temperature.
It turns out that it's not that simple.
Originally Posted By: Gokhan
So, 0W-40 is the thinnest oil in terms of the base-oil viscosity!
I'd like to point out that you contradict yourself in the same post.
Your first statement is correct, it isn't that simple. Did you look at the MRV values in the XOM blending table? Have you seen a 0w-40 with an MRV that low?
The XOM blending chart is a simplified piece of material designed to show blend-across ratios to achieve certain viscosity targets. It is in no way meant to be construed as universal or even indicative of XOM's own products.
The Harman Index as discussed earlier I think provides a lot more information here than simply assuming base oils based on this chart, particularly given that the chart is for XOM's range of PAO's, which represent how many current products we buy OTS? Possibly the only one close might be M1 EP 0w-20.
Let's look at a couple of Castrol products as an example:
Castrol 0w-40 and 5w-40.
Now, based on the Gokhan theory of relativity, the 5w-40 will have less VII because it is a narrower spread.
However, we know that GC 0w-40 has significantly more PAO in it than the 5w-40, which has basically none. The 5w-40 has actually proven to be a poor product with greater viscosity loss than the 0w-40 in application, which is blended with better bases.
The Mobil chart is a neat discussion piece when viewed in context. In application, ultimately cost dictates what gets blended and if you can hit your visc target with cheaper bases and more VII, what do you think gets used? That's what the Harman Index was trying to cut through, giving one at least a bit of an idea as to what the actual base oil quality might be rather than wild posit.
You also brought up TGMO:
Originally Posted By: Gokhan
So, 0W-20 is likely to have a thicker base oil than 0W-40! In fact in my UOA comparison of 0W-20 and 0W-40, I did find out that 0W-20 produced less valvetrain wear (less iron [Fe]) than 0W-40!
First off, you didn't actually measure wear. Secondly, you are using TGMO as your 0w-20 example, which we know is not PAO-based, and subsequently doesn't in any way compare to what's shown in that Mobil chart.
Comically, I think the only engine I recently recall hearing about timing chain issues with was the GM HF 3.6L V6, which I believe spec'd 5w-30
While I appreciate what you are trying to do here, I think that coming up with conclusions, let alone guidelines based on the data provided is a real reach. Perhaps Molakule can chime-in with some actual blend data to help make a clearer picture of the process used when developing an oil at a price-point?
