Originally Posted By: 13Tacoma
Awesome. Thank you.
Viscosity index is like a flow characteristic right? So the higher the vi, the faster the oil will flow to protect against wear especially at startup?
If that is correct then would vi be the most important characteristic of the oil and then followed by how light and the add pack?
Viscosity is the resistance to flow, viscosity index related to how viscosity changes with temperature...a higher VI will be thicker over 100C, an thinner below 100C.
Viscosity is what protects your engine, VI doesn't as two oils with same VI can have wildly different viscosities.
If you get an oil analysis, they will give you the kinematic viscosity at 100C, which is useful, but you can get pretty close blending using the mixing calculator
here
What you really want to be chasing is the ideal HTHS for your application, as it's representative of the actual viscosity in the bearings at high RPM.
See table two
here
TGMO is assumed to have an HTHS of 2.6, it's not published, just guessed at (some may say educated)...using the other oil that you wish to use, you can use the blending calculator to see what you end up with...minimum for a 30 grade is 2.9 HTHS, and around this HTHS should be your target if you want a "thin" 30...naturally occuring 30s without VII range up to and over 3.5 on that measure. Higher HTHS will correlate to higher film thicknesses.