Prius oil - dealer's choice?

I have seen a hybrid repair shop do a youtube about the new toyota 0w-8 oil and like water was described about it more than once in that video.

Here's another spooky looking u tube about water and the triple point .

I was told about this once when I was around 10. And it's one of those things I wondered about but never had tools available to explore much about it.

 

ExxonMobile isn't the only one leaving it off.

 

ExxonMobil has not even been publishing KV40 and VI lately.

Oil blenders are not required to publish any of these specs. Toyota never publishes any spec on TGMO, which is made by ExxonMobil.

In any case, for ILSAC oils, the HTHS viscosity will be at the SAE J300 minimum or no more than 0.2 cP higher than that minimum, as otherwise, it won't be able to pass the ILSAC fuel-economy tests. ACEA oils can have a much higher HTHS viscosity depending on the category, as the HTHS viscosity is also specced by the category for ACEA oils. In fact, most Euro OEMs only specify the HTHS viscosity, and they allow any SAE viscosity grade as long as the HTHS viscosity is as specified.

This is not something you can easily learn by Google'ing. You need to study papers and books on this subject or learn it from others. You still don't get it and are refusing to learn it. An oil blender not publishing the HTHS spec does not change the fact a bit that the HTHS viscosity is the viscosity that matters, and the kinematic viscosity does not really matter.

The oil pressure, for example, is related to the HTHS viscosity and not the kinematic viscosity, as well as the bearing minimum oil-film thickness (MOFT) produced by the viscous oil, the latter of which has implications on bearing wear. That's because the oil goes through temporary shear in the bearings that lowers the viscosity, and the bearings have the primary drop in the oil pressure.

Historically, the reason the HTHS viscosity was introduced into SAE J300 is because some multigrade oils, especially some of those with a large SAE xW-y spread such as SAE 5W-30, were resulting in bearing failures in the 1980s and up until early 1990s because the viscosity-index improvers (VIIs) temporarily sheared too much and the kinematic viscosity did not represent the actual viscosity in the bearings, which have high shear rates.

The above-mentioned problem with multigrade oils was mostly eliminated by incorporating the HTHS viscosity into SAE J300, even though permanent oil shear that is caused by permanent damage to the VII molecules can still be a problem, and higher-shear-rate parts in the engine such as the valvetrain can still experience a significantly more reduced viscosity than the HTHS viscosity due to larger—in fact, full—temporary shear of the VII. The latter, full-shear behavior entirely eliminates the viscosity contribution of the VII temporarily and effectively reduces the oil into the base oil and additive package. That is called the second Newtonian phase, where the viscosity no longer depends on the shear rate at very high shear rates, just as the first Newtonian phase, where the viscosity did not depend on the shear rate at very low shear rates. The HTHS viscosity is measured at a shear rate (of one million per second) near the middle of the non-Newtonian phase, where the viscosity gets lower with the increasing shear rate.

 

I didn't mention them not listing HTHS to say it wasn't important, but to point out that it isn't something shared.

 

Yes, and that's a pity that they don't share it!

Historically, Castrol has been really bad about it, publishing the minimum or maximum SAE J300 viscosity specs for HTHS, CCS, and MRV instead of actual specs. ExxonMobil has been bad with specs recently as well.