**Oil pan plastic cover help**

Here is the SAE J300 chart showing viscosity specs for engine oil. Note that viscosity grade 16 oil has tighter specs than VG 20...higher minimum and lower maximum.

Possibly of interest, automotive gear oil had its own chart, and viscosity grade numbers of 70 and higher denote that the product is gear oil, not engine oil. The viscosities don't rise according to the numbers, e.g., vg 90 gear oil is about the same viscosity as vg 40 engine oil, but it is a very different product with an additive package to suit the usage.

 

Note that SAE J300 does not specify the kinematic viscosity @ 40 ℃ (KV40). KV40 along with KV100 determine the viscosity index (VI).

In a multigrade oil, up to around 40% of the HTHS viscosity may be contributed by the viscosity-index improver (VII), which is a polymer (plastic), and the rest is contributed from the base oil. The problem is that the VII does not work in high-shear areas of the engine such as the valvetrain and parts of the ring–cylinder system because its molecules fully align with the flow under high shear, the viscosity being reduced to the base-oil viscosity as a result. Note that the shear rate is the relative speed of the sliding parts divided by the oil clearance between them.

The more the VII content, the higher the VI is. TGMO 0W-20 SN had an ultra-high VI ~ 230, and its base-oil viscosity @ 150 ℃ was ~ 1.6 cP. In high-shear conditions, its viscosity is reduced to its base-oil viscosity ~ 1.6 cP from its HTHS viscosity = 2.6 cP. Therefore, TGMO 0W-20 SN, in high-shear conditions, was basically a SAE 0W-8 with an HTHS viscosity ~ 1.7 cP. The Toyota engines running TGMO 0W-20 SN fared well (mostly), which shows that they would probably run fine even with a SAE 0W-8.

The long story short, TGMO 0W-16 SP should be OK in engines that previously ran the ultra-high-VI TGMO 0W-20 SN.

 

Typo. 10w-20 should read 0w-20.