0W-X Benefits

[modularv8]

We know that 0W, 5W, 10W, etc is related to SAE cold cranking maximums, cold flow properties of a lubricant at very low temperatures. A better indicator of cold pumping flow is the MRV. What is interesting is the effect of an 0W-X lubricant at engine operating temperature. The lower the CCS or MRV for a given HTHS @ 150C (or viscosity grade), the greater the fuel economy (from 2 to 3% increase in mpg). For instance, two motor oils each with HTHS @ 150C; one with CCS of 6000 cSt/-35C and the other with CCS of 3000 cSt/-35C. The lower CCS motor oil will have ~3% increase in mpg over the higher CCS at engine operating temperature.1

Another interesting characteristic of 0W-X oils, is there ability to form greater oil films at the piston rings compared to a lubricant of the same grade/HTHS. For instance, a 5W40 will form a greater oil film at the piston rings than a 15W40. In addition, the lower the viscosity grade of a lubricant the lower the CCS/MRV leading to greater fuel economy and oil film at the piston rings.2

And finally, it is extremely difficult to formulate a 0W-X lubricant with a low CCS/MRV without the base oil formulation being pure PAO/Ester. Mobil 1 Advanced Fuel Economy 0w20 or 0w30 with their extraordinarily low MRV could only be formulated with PAO/Ester.3

Summary:
- 2% - 3% increase in mpg for same grade/HTHS.
- Increase film thickness at piston rings for same grade/HTHS at operating temperature.
- Ultra low CCS/MRV synthetic 0W-X. formulated with PAO/Esters

1. Research on Environment-Friendly Gasoline Engine Oil
of Ultra-Low Viscosity (2001).

2. Improved Fuel Efficiency by Lubricant Design : A Review(2000).

3. ExxonMobil Synthetic Basestocks Formulation Guide.

 

[mechanicx]

It seems to me though that a 5W40 formulated with the same level of POA/esters would have the same characteristic of film strength at rings as say a 0W30 and lower volatility. AFE does not have very high HTHS. But good info and hard to argue with your sources. I do think the fuel economy benefits is optimistic especially if temperatures aren't very low.

 

[modularv8]

I agree. The reports does not investigate if the thicker film has greater film strength. I guess it depends on the measured HTHS value for a given lubricant. Interestingly, a synthetic 5w30 uses about 8.5% VII, while a 0W30 requires 9.5%. But the result is a slightly lower HTHS and a signficant drop in the CCS/MRV for the 0W30.