My Concerns with the New Prius

Re: gasoline weathering
(1) I am not aware octane goes down on sitting in can ..can get some C4/C5 etc evap over time in a plastic can
(2) I am not aware Premium degrades slower (as per Fuzzy1, E0 may be better if avail)
(3) Not aware gas tank material of construction change in plugins
(4) Don't know why some tools might require mid-grade over regular

For a USA plug-in you'd want a major brand listed as Top Tier...I see Consumer Reports has a 2022 article on this. I'd go for E0 Top Tier if I had a choice for sitting in tank unused for long months (mute point since I do not have the E0 choice).

Top Tier Gasoline Is Worth the Extra Price, AAA Study Shows - Consumer Reports

 

(1) Stored gasoline goes bad/stale over time due to oxidation and evaporation that cause changes to the blend. Those changes can lead to changes to the octane. Gas isn't a liquid of a single chemical compound like water and ethanol. The higher octane compounds tend to be lost or change to lower octane ones as the gas ages.
(2) I'm unaware of premium degrading slower than regular. The aging process proceeds at the same. Starting with a higher octane just means there is a better chance of the fuel meeting the minimum octane requirements of the engine after being stored. The gas could still end up bad for other reasons. Ethanol comes with water, which could aid the degradation process, or allow microbes to grow, or lead to phase separation if more moisture gets in.
(3) It's more likely the evaporation system has a tighter seal for PHEVs. Most are aiming for a cleaner emission rating, and to keep air and moisture out.
(4) I just know the ones I've owned that did seemed to run fine regular.

 

Sorry if this has been well covered on this forum, but I want to really emphasize part of what was just said: use Top Tier fuel.

Top Tier is a voluntary fuel standard developed by a group of automakers(including Toyota). Any fuel distributer can label their fuel Top Tier as long as they meet those standards(mostly to do with keeping out contaminants and including certain levels of certain detergents).

For a retailer to use the Top Tier logo on their pumps, ALL their fuel grades need to be Top Tier. So as a buyer, you don't have to worry that 91 super unleaded is any better for your engine than 87 regular(assuming your engine doesn't require 91+).

In an engine that can use 87, a Top Tier regular 87 is generally better than a non-Top Tier super unleaded 91.


Here's a partial list of retailers/distributers that adhere to the Top Tier standard: 76, Aloha Petroleum, Arco, Beacon, Breakaway, Cenex, Chevron, Citgo, Conoco, Costco, CountryMark, Diamond Shamrock, Express Mart, Exxon, Fast Fuel, GetGo, HFN, Harmons Fuel Stop, Hele, Holiday, Kwik Star, Kwik Trip, Marathon, Meijer, Metro Petro, Mobil, Ohana Fuels, Phillips 66, QT/Quik Trip, Reeders, Road Ranger, Rutter’s, Shamrock, Shell, Simonson, Sinclair, Sunoco, Texaco, Valero, Value America, Wow, and Win Win.

TOP TIER™ Gasoline Brands

Automakers/engine makers that developed/recommend the standard: Audi/VW, BMW, Fiat-Chrysler, Ford, GM, Honda, Mercedes, Toyota, Detroit Diesel, Navistar.

 

But what do you do when they recommend Top Tier premium octane fuel, in a Prius?

 

Then you put in Top Tier premium octane fuel? I don't really understand the question.

Octane and fuel quality are two different things. Higher octane on its own doesn't make fuel better for your vehicle unless it needs it for proper operation(usually due to a high compression engine). All other things being equal, paying for 91 octane for a vehicle designed to work just fine on 87 is a waste of money.

Now, some fuel retailers put different additives in their different fuel grades in order to justify the increase in price. In those cases, the premium 91 is better than the regular 87, but it's not because of the octane rating.

With Top Tier, you don't have to worry about that. If your manual says 87, put in 87. If it says 91, put in 91. All the grades of fuel at that pump will meet the higher quality standards.

For example, the 2022 Prius Prime needs 87 octane using the (R+M)/2 standard that the US uses, or 91 octane using the RON standard. (Same fuel, just two different ways of measuring the octane.) Thus, there's no benefit in putting 91 octane(US system) in the gen4 versus 87 octane.

Now there's reason to believe the gen5 will want at least 91 (R+M)/2 or 95 RON. If I had to guess, it's because the compression ratio in the new M20A-FXS(14:1) is greater than the older 2ZR-FXE(13:1). Also, the intake valve timing in the M20A can be adjusted much further than in the 2ZR, so maybe that plays a factor.

That would explain why the small text in gen5 press info says it will get more power with 91+ fuel. The fuel/engine management system will likely be able to tell what kind of fuel is being used. If the octane isn't high enough(the computer starts to detect premature detonation/knocking), the engine can adjust the valve timing to lower compression to account for it. But while that will stop the engine from knocking, it also means the engine isn't able to take advantage of its full potential. We'll see when the final manual is released, but if it ends up saying 91/95, that's what you'll use.

But on the flipside, a few Toyotas already use the M20A-FXS and its siblings and none of those require higher octane fuel, so...

 

The fine print about octane and max power is on some of the Lexus models.
Depending on how marketing feels, it may not appear on the Prius site when the 2023 officially arrives. It isn't unheard of for a car company to list a car as regular fuel, and act like higher octane won't make a difference for engines in which it can, in the name of protecting sales.

 

I'm under the understanding that Toyota is recommending BOTH Top Tier fuel AND 91 M+R/2 octane (aka. Premium Fuel) at the same time in the new Prius. In other words, the new Prius is apparently NOT designed for good ol' regular 87 octane fuel.

 

only if you want the full hp

 

What about full MPG?

 

Pretty sure Toyota recommends Top Tier for ALL their vehicles. Since they were part of the crew that drew up the Top Tier standards, it makes sense. Probably especially so for all engines that include direct injection. Thankfully the gen5 2.0 engine has both direct and port injection, so at least it has a prayer of keeping those valves relatively clean.

 

Yes I know that. I use Top Tier in all my Toyotas. But they haven't mentioned needing premium fuel until now, at least not in a Prius.

 

They’ve said in order to achieve a certain performance they were using higher octane, non-ethanol gas. In a very preliminary blurb.

 

US regular tends to be lower octane than the rest of the major markets 87 AKI is close to 91 RON, but not quite the same. Some places have a higher RON for regular. We should have switched to RON when cars stopped coming with carburetors.

Engine companies design for the RON octane, and then detune the engine for US gas. It's easier than going the other way. Mostly, it is just letting the ECU handle it. The 1.4 turbo in the Sonic was labeled regular, but was designed for premium. Other times, it took more. The US SkyActiv g had a 13:1 compression ratio when introduced in the US, but was 14:1 elsewhere.

I experimented with octanes in that Sonic. You might see better fuel economy with premium when not pushing the Prius for power. For the price per mile to break even, the price difference can't be more than 20 to 25 cents a gallon. Around here, it's been at least twice that for years.

 

i only saw hp. it's in one of the threads on the new specs

 

HP doesn't have the list of YMMV variables to cover differences, and it is probably easy the measure now with a smart phone.

The fuel fine print for MPG results would be, "Results achieved with a defined gasoline blend that is 93 octane and ethanol free." For CARB, it would be 91 octane. Which raises the question of why is California premium just 91 AKI, and not 93?

 

Likely to favor less volitiles and carcinogens


Wisconsin premium is rarely above 91, the highest efree I ever found was 92
The one station in the county with 93 is definitely full of 10% ethanol.

 

Re: Point 1.
The lighter volatiles (the stuff they blend in for higher octane ratings - commonly xylene and toluene) in gas evaporate at a faster rate. As well, and critically more with ethanol content, some level of moisture absorption does occur over time as no canister is perfectly sealed (and shouldn't ever be - gas needs venting)
Storing 87 octane for a year in a wet coastal area will have the octane degrade below a safe functional rating without stabilizers. Conversely, storing 91 octane in a dry locale with relatively high dew points all year round may allow the gas the "survive" at 89 or 88 octane within a two year period, no additives needed.
As for point 2, premium gas and any fuel with a higher eth fraction, absolutely will degrade faster. The use of lighter hydrocarbons, and ethanol being more hygroscopic and a lighter hydrocarbon, to attain the octane rating means they will evaporate from the blend the quickest.

As for the rest of the thread's gasoline/M20A/general car conversation,
All vehicles benefit from using a Top Tier rated fuel. Every single one, without question. Regardless of if it is a 60 year old engine or the manufacturer doesn't state it in the manual.
A 10% ethanol blend means most gas for most people will yield ~3% lower MPG than pure. The blends change seasonally and with economic forces. Your E10 gas may actually have 7% eth (don't tell the EPA, please, the refineries just didn't have enough supply), or 15%.
If you want to truly have answers as to 87oct (91 RON for the rest of the world - and I know Europe regulated 95RON minimum a while ago) and the effects on the ICE, I would suggest purchasing an ELM327 OBD adapter, using the Torque app, and watching your engine's Knock Sensor report under gas-powered acceleration and fully-warmed high speed cruise. From an engineer's perspective, an ideal engine should never report more than ~2-3 degrees retard. YMMV, and you should assume any and all long term effects from forcing a non ideal knock situation, and you should never assume "the computer can compensate" actually means it is good for long term reliability.
As for seeing 85 octane in some places, it's because >~7000ft elev. the thinner air allows a lower octane. A higher octane will not restore any power or MPGs in this situation, as the air is at 78% and less density, which directly translates to the lower power output of the ICE.
87oct in a motor built for 91 definitely decreases both power output -and- fuel efficiency. The ECU has to pull timing, this means less power per unit of air, less power per full 4-stroke cycle, which especially for a design like the M20A-FSX, will give a lower MPG and a less efficient battery-charging.

In summary,
While each indivudual effect of octane and gas blend is not vastly significant, the compounding effects of both an ethanol gas and a lower-than-prime octane is likely to reduce (ICE) efficiency on the order of ~5-6% absolute.
I can only speculate without a 2023 PHEV in my hands, but I would imagine a "worst case" scenario of 15% eth 87 octane reducing a full-tank range (assume no plug in charging to remove variables) down from "600" to "550"

We could also go into detail about how ethanol fuels scrub lubrication from the upper cylinder, and everyone really should be putting 1 ounce of TC-W3 grade ashless marine 2-stroke oil in their gas for every 5 gallons to mitigate this problem, but that could be going in too deep?

 

We could also talk about how a little water in the ethanol protects aluminum parts.

How likely is labeled E10 to have higher than 10% ethanol? I didn't think it could go over 10% legally. Going over will get the octane rating a slight bump up. Heard 7% was all that was needed for meeting oxygenate requirements, and those are mostly in place for carburetors.

Couldn't the TC-W3 contain additives poisonous to the catalytic converter?

 

My Toyota owner's manual says not to use E15. So I sure hope that E10 is not actually E15.

 

New photos from a Japanese auto show: https://spyder7.com/article/2022/11/30/17004.html

Lots of angles of supersonic red. First photo I've seen of the 8" display. Confirmed spare tire on at least the Japanese spec HEV.