Sunday 40w discussion

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Originally Posted by Shannow



If I had a narrower operating environment, a 15W30 would be my preference over a 15W40.




Like this ... the only brand I have seen in this grade. Sure there are others, but I've never seen them ...

[Linked Image]
 
Just picked up some T6 15w40 to try. Truck is a 2018 Ram 3500 6.7. I've never ran a UOA but may do that coming up.
 
This topic is being discussed in the PCMO thread about the base-oil viscosity, which I called HTFSV (high-temperature, full-shear viscosity):

HTFSV: high-temperature, full-shear viscosity

The very first base-oil viscosity (HTFSV) table I calculated doesn't have the density correction factor and VII adjustable parameter optimized. Refer to the later tables in the thread for more accurate values of the base-oil viscosity.

Chevron has a very nice brochure about their Group II oils. It's very informative indeed. One of its pages is dedicated to the base-oil viscosity. They explicitly and very confidently state that:

  • "Heavier base-oil viscosity improves performance"
  • "In HDMO (HDEO), wear decreases as (base-oil) viscosity increases (from 5W to 10W to 15W)"
  • "Commercial proof: Proof that a heavier base-oil viscosity is critical to wear control."

Therefore, they go as far as saying that they have proved the base-oil viscosity to be critical to wear control.

They did their tests on a mini traction meter (MTM) using both experimental oils (5W-30, 10W-30, and 15W-30) and commercially available oils (5W-40 and 15W-40).

The results were such that the 5W-30 produced more wear than the 10W-30, which in turn produced more wear than the 15W-30. The CJ-4 5W-40 produced more wear than the CJ-4 15W-40. The results are the same for both fresh and sooted oil.

[Linked Image]


Here is the full Chevron brochure:

Chevron Group II base oils: optimise automotive engine oils
 
Would you agree with this.....

HTHS is the driver for fuel efficiency at operating temperature, while VI is the driver during warm up.

I conclude from the Chevron presentation, that a redundant "W" winter rating may yield slightly higher wear rates in specific tests, but the use of engine oils such as 5W40 may improve fuel economy compared to 15W40 with the same HTHS.

In a warm climate, would a 0W20 engine oil improve fuel economy compared to 20W20 of the same HTHS?

A. Yes
B. No
C. Only during warm up.
D. The 20W20 would be more fuel efficient at operating temperatures because the KV100 is lower than the 0W20.

Edit; What about wear, 0W20 vs 20W20?
 
Last edited:
10w30 would be more shear stable the a 5w40 and even a 15w40 in most cases so not sure why one couldn't use a 10w30 all the time. There are some 10w30 full synthetics that really are a straight 30 weight oil but qualify as a 10w30. They use no VM at all. All the heavy commercial truck engines doing far more than any PStroke is going to do are factory filled with 10w30 and using it year round from the southern deserts to the sub arctic. I would just use a good quality 10w30 full syn HDEO and call it a day.
 
It's Sunday already in some parts of the world.

TiredTrucker in the above post suggested (again) that there is a relationship between engine size and GVW, to engine oil viscosity.

What should I do?
 
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