Chosen Oil Viscosity...?

Knowing Toyota's engineering, your best bet is to use what's on the oil refill cap 0W-16. It'll even say in your maintenance book that using 0W-20 is okay but only for one oil change, the next has to be 0W-16. It can get down to -20 and up to 110 here in Colorado and has worked just fine in my 2021 that takes 0W-16. If you're worried about high temps, just change the oil often and, also, the radiator coolant.

 

From previous cars Toyota usually calls for changing the oil sooner when not using the recommended viscosity.

They designed the engine for 0w16, and it is what is used to get the EPA numbers. The viscosity has been out long enough that finding it in the store isn't a problem, and it has been used in Japan for years before manufacturers started calling for its use in US models. Some Toyotas here might be calling for 0w8 now. So I would not worry about using 0w16 when it is called for.

If everything is working as intended, the engine cooling system should be keeping things within the proscribed temperature range regardless of the season. Using different viscosities seemed more important in colder climates where the oil can end up too thick on start up from what was in past car manuals.

 

There is absolutely no need whatsoever to stray from SAE 0W-16 in a newer Prius unless you are driving the car really, really hard and/or fast. The engine barely warms up and/or experiences much torque in regular driving.

 

IIRC Toyota switched the Gen 4 oil spec from 0W20, to 0W16, 2~3 production years in. Same engine, same car.

Which leaves me sceptical, of the importance to use one and not the other. Suspect it’d hardly skip a beat, even with say 5W20 or 5W30 (the latter was Gen 2 spec).

 

The lowest viscosity that is needed is the best viscosity for your car, as it will result in the best fuel economy, smoothest and most responsive engine, and longest engine life.

As I said, the exception is if you drive really hard or fast, in which case, a higher viscosity may be better for engine longevity.

 

Like pulling the grapevine?

 

0w-16 is not all that much different from 0w-20 . I've used both when changing the oil in the Gen 4.

Costs can be the same for both 0w-16 and 0w-20 if you shop around on the other hand there can also be a big difference in price if you don't shop around.

Toyota now makes 0w-8 - but it's easy to get a 5 quart jug of 0w-16 or 0w-20 for the same price as a quart of 0w-8 , no matter where you find 0w-8 for sale presently.

 

if 0w8 oil becomes more widely available in the future, should 5th gen prius owners consider adopting 0w08 if when the cost of 0w8 would be at par with 0w16? or stay with 0w16 like what the oil cap says?

 

You might want to ask that question, if / when 0w-8 comes down in price and after more owners have compared it with both 0w-16 and 0w-20 oils.
Typically the General Consensus Consensus decision-making - Wikipedia
is to stick with the viscosity that is recommended by the manufacturer. Use other viscosities at your own risk.

 

Use what your motor calls for.
Since ours is 0w-16… continue to use that even if 0w-.005 comes out.

 

I have 0w20 in my Gen 5 right now, the reason? I have a bunch of it (Pennzoil Ultra Platinum) and when i used to work at a Toyota dealership, we had a bulletin from Toyota basically saying ''use 0w20 for as long as the shortage of 0w16 persist''.

When the stash will run out, i'll be tempted to give the Hybrid oils from Amsoil a try.
https://www.amsoil.ca/p/amsoil-0w-16-100-synthetic-hybrid-motor-oil-he016/

 

From Toyota EU site for 2023 Prius PHE, looks like a whole range is acceptable even though 0w16 is preferred. US manuals do not show the range by expected temperature

****

 

This exact thing you posted is a repeated boring discussion that happens on BITOG everyday. If you go there, you will be told to use SAE 0W-40 because of the CAFE conspiracy in the US.

The truth is that there is nothing to gain in a Prius by going thicker than SAE 0W-16. The engine hardly ever warms up. However, if you use a thicker oil, you will have a more sluggish response and worse fuel economy.

In fact, the new Corolla, which has the same engine as the new Prius, is recommending SAE 0W-8.

 

Probably because the temperature spread for the oils are virtually the same, and Americans are easily confused. All that graph says is to not use a 5w- oil in near arctic temperatures, otherwise, any of the three is okay. Toyota says to change the oil sooner if not 0w-16 cause the thicker will have a negative impact on engine performance and efficiency.

 

Are you saying that when I am blasting down the interstate for hours on end at 80MPH engine is not 'warmed up'?
Are you saying you can quantify statements like: "more sluggish response and worse fuel economy".
As in, accurate numbers comparing ever so slightly different weight oils? That's some detailed testing!!

 

I don't think 80 mph is considered a very high speed for Prius—regardless, you should always stay at or below the speed limit by law—but the Toyota owner's manuals always provide a note that a higher viscosity may be better suited for extreme speeds. So, perhaps if you are regularly driving 90 mph or faster, you should use 5W-30.

 

Very good. I drive at most +5 the posted speed limit, so on some local interstates that would be 85mph.
I'll have to RTFM. It recommends 5W-30 with some duty, in writing? What if it's 0°F and I'm taking a road trip?

But what about my questions concerning your statements above?
"The engine hardly ever warms up...."
"...you will have a more sluggish response and worse fuel economy." As in 0-60 times? A measurable drop in mpg?

 

A 1.9% minimum improvement in fuel economy is required for 0W-16 over SAE 5W-30 in ILSAC tests. It is 0.7% minimum required for SAE 0W-20 over SAE 5W-30. You will probably see more benefit if the engine is not fully warmed up. You could see improved protection in extreme cold as well, and the engine could operate more smoothly during warm-up.

 

Sluggish response... mehhh...
Reduces fuel economy, yeah a bit..
Engine hardly ever warms up! Yeah definitely! The thing always start then stops every 2% of indicated battery level.. that is the crap that got out of my engine because of this... 10k km OCI so, 6k miles? Never again! I'm not going over 5k during winter just because of this. Can't get the damn thing at decent oil temps..

Oh and if you're wonderimg, that was some Pennzoil Ultra Platinum in 0w20 flavor with a YZZF1 OE filter.