My Concerns with the New Prius

Manuals are available now, at Toyota Tech Info.

 

From the Prius Prime Manual:
"87 (Research Octane Number 91) or higher"
So not Premium then?

 

That's right, in the USA we use the first number, denoted as AKI, and 87 AKI is not premium.

 

i think the small print said premium if you ant full performance

 

That was on one of the early publicity videos. It is also on some Lexus models. Could be true, but I'm leaning towards the inclusion of the small print being because someone confused the RON figure with AKI.

Unrelated, Japan is moving towards, and most of Europe is already at, having 95 RON be the minimum octane at the pump.

 

14:1 compression ratio... Higher octane = less knock = more timing = more power.. Enough to offset the increased cost, I do not know...

 

Outside of performance cars, it will result in better fuel consumption. Carbon emission reduction is a main reason for this shift in other countries.

My comment about octane was because I had recently stumbled across a 2018 study on the US switching to 95 RON by 2023. Between the increased utilization of refinery equipment, and the general trend in improve fleet fuel economy. The prices may not have shifted much. The alignment of major car markets to the same RON should lead to cost reductions in engine design to pass on to consumers.

Just switching to RON from AKI would help with the latter. It is also a better predictor of the fuel's behavior in fuel injected engines.

 

I did see better mileage with prem. on my other Toyota. Frankly that engine plain sounded like crap with regular. I haven't noticed any audible knocking on the Prius. I'm near due for a fill up in the Prius. I'm going to take a quick data log, then fill it with premium and do another one. (we get the good stuff up here) Then I can compare the average advancement/knock count to see if there's really any gains to be had.

 

That is expansion rate. The actual compression ratio is significantly less, because this is an Atkinson-cycle engine.

At any fixed ethanol level, higher octane typically has slightly lower energy density. Though the details vary depending on blending and particular batches, and specific batch details are not normally publicly released. At least according to my relatives who where in charge of gasoline blending years ago.

 

Engines run at the cusp of knocking. Ignition timing advances until knock is detected, then the ECU backs off the timing until it stops. That cycle is continuously repeating. Engines running smoother on higher octane are likely a case of the timing being advanced to the maximum, and knock still not being possible. Smoothness aside, there probably ws no other benefit to using that fuel.

As for that other Toyota, I know that Toyota recommended midgrade for some models in the past. Regular won't cause harm, but the engine can take advantage of higher octane for better efficiency.

Seen the same about the energy density. In an engine with a compression ration to make use of the higher octane will be more thermally efficient. Which can go beyond just making up for the lower energy content.

 

Has anyone tried using ethanol free gas? I'm trying to find out if it's worth the extra cost.

 

For the price difference I've seen, it would have to net 20% or better fuel efficiency.
Trying out E15 might be a better try for cost.

 

I use it, but I agree with Trollbait that it's not worth the cost on an efficiency standpoint. I'm using it more to get the maximum life out of the fuel system, especially in my climate and with my driving habits. Ethanol-free or not will show no differences within the first 5-7 years, and probably not out to even 10 years, but beyond 10 years you have less risk of fuel system corrosion with ethanol-free.

Gas with ethanol can hold more water in suspension than pure gas. If you have wild temperature and humidity swings like my region, that water can separate out and possibly help corrode anything metal in the fuel system. The problem can multiply if you don't drive a lot and the fuel sets in the tank undisturbed. Plus my region can get to -40F/-40C in the winter, so I like to have as little water in the fuel system as possible.

My plan is to hold onto the car for 10-15 years(I owned my last Prius for almost 14), so I feel it's worth it to me. I'm an outlier, so what's worth it to me is probably not worth it to you. If you don't plan to own the car 10 years, or you have a moderate climate, or you use enough fuel monthly that it doesn't have a chance to absorb moisture, then it's likely not worth the extra cost.

 

From just a fuel cost per mile basis, almost certainly not.

While various users have reported wildly different results, careful federally-funded lab tests on dynamometers have found results consistent with the theoretical difference in energy content: E0 should be about 3.3% better than E10, and 5% better than E15. The hard part is finding any retail outlet selling it for a price premium that small. Because some consumers want it for several other reasons unrelated to MPG, prices run higher than that.

 

You might be onto something. I’m thinking ethanol free might be a very wise choice for people with primes that very rarely, if ever use HV and commute solely on EV. With no ethanol in the fuel, it should technically be able to sit significantly longer without degrading.

And yes, I do realize it’s not good to let a tank of gas sit in the vehicle for months and months without use. Probably still a smart idea to push the HV button and let the engine run at least every couple weeks.

Edit: the nearest ethanol free station is 45 minutes to an hour away from me up north so not feasible on a consistent basis. I guess unless I’m in the area, so probably not even worth it and I’ll just be probably pushing the HV button whenever I hit the highway to keep the reg 87 gas flowing occasionally.

 

I don't recall any previous Prime owners reporting any problems when following Toyota's advice on aging fuel.

Here is what the 2023 Prime Owner's Manual says:

 

My gsxr motorcycle has a 12.5:1 compression ratio and I use 87 octane without a problem. My other motorcycle zx14 has a 12 to 1 compression ratio same thing. I even use 87 octane in my Corvette. I don't have any problems

 

Just because you've accepted less than optimal performance by cheaping out on fuel below manufacturers recommend doesn't make it correct.

 

That depends on your personal definition of "optimal performance".

If he is getting sufficient power for his wants, and prefers to then go for lowest fuel cost per mile, may he is getting his desired and correct "optimal performance".

 

I'd recommend a scooter then. Buying a high performance vehicle and throwing it away over an arbitrary uneducated opinion is waste plain and simple.