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.
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.
Reviving an old thread here. How would any of you feel about using a 0w-12 oil in a 2023 Prius? I am considering HPL Premium Plus. The viscosity at 100C is 6.01 vs. a minimum of 6.1 per JASO300. I think the HTHS viscosity is on the order of 2.1 for the 0w-12 vs 2.3 for the 0w-16. HPL Premium Plus is known to thicken over time and we all should know that the Japanese have been experimenting with 0w-8 for close to a decade. The use case for this vehicle is mainly five miles each way to and from work so I know it won't matter. The bigger question is what may happen should we decide to take this vehicle on an extended road trip in hot weather.
Why not try the TGMO 0W-8 from the dealer (OEM oil for the new Corolla)? You can post on BITOG, which has become the promotion site for HPL.
You can PM me here, but I don’t have much suggestion. I see that the nonhybrid Corolla engine is very similar except for 13:1 compression vs. 14:1 for the Gen 5 Prius. 0W-8 would probably work though unless you are driving very fast on the highway for a long time (high oil temperatures). HPL uses higher-quality base stocks but generic Oronite additive packages. TGMO is custom-blended by ExxonMobil and has a high moly (for fuel efficiency) and high boron (for sludge dispersancy) content. It tends to contain a dash of polyol ester (POE) for piston-ring cleaning as well.
The 13:1 to 14:1 compression ration is really only a difference in expansion. The max pressures seen in the cylinder during compression will be virtually the same between the engines. There might be a difference in the piston rings because of the different oil requirements.
The piston-ring set is the same for both variants: Toyota part no. 13011-24040. How can the final pressure be the same if the compression is different? Isn’t the starting pressure always the atmospheric pressure?
The same way your Prius has a compression ratio of 13:1 while having an effective one of around 10:1. Go above 13:1 compression with direct injection, and you will start getting knocking with US regular octane.
I see—since the intake valves don’t close immediately at the beginning of the Atkinson cycle, the air–fuel-mixture compression is less than the geometric compression. In any case, regarding the oil viscosity, the critical factor is probably the brake mean effective pressure (BMEP), which is the ratio of the torque to displacement, which seems to be the same for the Corolla and Prius variants. The minimum oil-film thickness is inversely proportional to the load density, which is related to BMEP, and directly proportional to the oil viscosity.
I was asking specifically about 0w-12 HPL Premium Plus with properties so close to that of a 0w-16 that it probably won't matter. Presently I have 0w-16 HPL Premium Plus on hand waiting for the vehicle to turn 50k. In other words this is a purely academic discussion for at least another year. I may revisit it after 10k miles on HPL 0w-16.
A better question is, what are you trying to gain with a boutique oil? As we all know, you can’t make a better oil by simply putting more additives or PAO and POE base stocks. In fact, it is funny that HPL even lets you design your custom oil. There needs to be a delicate balance between the additives and between the additives and the base stocks. HPL hypes their oils by saying that they use more additives and more quality base stocks. Do they actually test if their recipés work? They don’t. The only thing they do is to run them in some race cars and claim that they perform in an excellent manner. Last but not least, their oils are not certified by API, ILSAC, ACEA, OEMs, etc. You don’t even know if the HPL oils have seal compatibility (no seal shrinkage or excess seal swelling). You can use any oil you want. I would personally stick with TGMO, which is custom-blended by ExxonMobil. Mobil 1 and Pennzoil Platinum would be good choices, too, and probably also Castrol and Valvoline. As for the viscosity, Gen 5 would probably be fine on SAE 0W-8. Perhaps they will switch to 0W-8 in the 2026 model year. In Gen 4, they switched from 0W-20 to 0W-16 mid-cycle while there were no changes in the engine.
