What do you fill it with? Is 10% ethanol OK?

E10 (or E15) is all I have ever used in each of my Prius for the past 23 years.

 

I think in the States 10% ethanol is virutally the norm, mandated. Similar up here, at least for regular.

 

Yes it's okay. It's difficult to find any gas that does not have ethanol blended in. If you do find it, it's much more expensive. I believe the manual says up to 15% blend is okay.

 

10% ethanol, a.k.a. E10, should be good in virtually all modern cars, by long ago EPA mandate. As mentioned above, you will have great difficulty avoiding it.

Look at your gas cap, it should have the answer printed right on it. E.g. my 2012 Prius clearly shows to not use E15-E85. Your newer model likely shows E15 is acceptable, but not E85.

 

Yeah one heck of a jump, from 10~15%, to 85%.

 

I have begun using ethanol-free gas exclusively. I'd like to know if others notice the same benefits as I? To wit: the engine runs noticeably quieter with much less "valve noise" (if that's what it is) at WOT, admittedly rarely called for. There also seems to be a more robust power band. Subjective, yep. But I've always wondered how that Atkinson cycle design can work so well on 87 octane fuel. What is it? 13:1 compression ratio? Granted the power curve is more gentle, but? Anyway, my read is all that "thrashing machine" racket being gone now is worth the extra cost in fuel. I imagine my engine is happier. If I must use ethanol-adulterated fuel, I get 93 octane, which also reduces the thrashing machine effect. Self hypnosis? I'm not sure.

 

I live in a state (Minnesota) where E10 has been standard for decades. You can still get no-ethanol has, but there's no point. Questions like yours were answered long ago. There's nothing to gain.

 

The Atkinson engine has variable compression ratios for the strokes/cycles. Compression ratio is the term used for the engine spec, but it applies to the expansion/power stroke of an Atkinson. The compression/charge stroke compression ratio is around that of a regular octane Otto cycle engine. Real Atkinson engines accomplish the compression ratio difference by having a cam between the piston and crankshaft. The Atkinson engines in hybrids are Otto engines in which the intake valves are left open at the start of the charge stroke to get the lower compression ratio. Add a turbo and you get a Miller cycle.

Ethanol free gas as slightly more energy(3%) than E10. That will mean better efficiency per gallon, but not worth the price increase I see. Won't explain what you report. If it isn't just placebo effect, quieter running could happen from higher octane. There is also the possibility of different cleaners or contaminants between the fuels you're using that result in what you experience.

 

I think there is no question that ethanol in the fuel is damaging to our fuel systems. It may not explain the admittedly subjective perception, true enough. But especially with my Prime, where I may not refuel for more than a month, I will continue to source ethanol-free fuel. I challenge Prius owners to try ethanol-free to see if their engines sound different at high rpms. Mine certainly does, and the power pulse feels like more than 3%.

 

Finding ethanol-free is a challenge though. Up here one ready source is Chevron’s highest octane (94 IIRC). Pricey, and what are the ramifications of the high octane? I know it resists combustion better, more suited for high compression engines. And it’s a lot more expensive.

 

...for millions of owners.

If there was damage, how come there are no repairs? How come we routinely see gen-2 Prius on the road still? For that matter, I still see the classic model from time to time.

It's a dead topic here where you'd think it would be most common.

 

Saw a Gen 1 Prius on the road yesterday. The elder couple in the car might have bought it new- couldn't tell the year, it must have been a 2001 model. Still on the road after 22 years!

 

Time to go into teacher mode for a bit. Sorry for the length.

How can ethanol damage a car:
Ethanol is hydroscopic. That means it attracts and absorbs water and holds it in suspension. Pure gasoline is hydrophobic. This means that water almost immediately separates out of pure gas just like with cooking oil and water. Because of these respective properties, small leaks in gas station fueling systems can go undetected more easily in tanks using ethanol blends versus pure gas. It also means that moisture in high humidity regions can get into those ethanol blends.

So what happens to your car when your ethanol blend is contaminated with water? The water will slowly corrode anything in the system that is reactive with oxygen. Prior to the 1990s(?), much of the fuel system in cars was made of metal. Running ethanol blends would lead to corrosion of fuel tanks, pumps, lines, injectors; it could ruin the entire system if the fuel was routinely contaminated with water. But sometime in the 90s(?), the US mandated that all cars be built to handle E15. This regulation forced automakers to remove almost all reactive metals from the fuel systems and switch to mostly polymers.

So what about today and a modern car? While almost all metal has been removed, that is not the same as all metal. There are still a few areas in the fuel system where metal must be used. Automakers try to protect that metal as best they can, but no system is perfect. I'm mostly talking about the fuel pump, the high pressure fuel lines(in direct injection cars) and the injectors. All of those are going to contain metal that might be able to corrode over time and prematurely fail.

So that's why seeing a gen1 or gen2 on the road doesn't mean much for this debate. Many of those might have had their fuel pumps replaced and you'd never know just by looking at it. A fuel pump replacement isn't expensive enough to junk the car over it. Same thing with an injector or three failing over 20 years. You'd just replace it and keep driving.


Personally, I'm running pure gasoline because I'm trying to keep my car in as perfect mechanical shape as I can, and I'm willing to pay the premium in fuel costs to do it. But I don't automatically recommend that everyone do the same. My monthly milage is low enough that an extra $5/month or less for pure gas instead of E10/15 is worth it to me. If I had a regular commute and was having to fill up multiple times a month, I'm sure I'd make a different decision. Also, the gas station at my grocery store and another gas station very close to my home both have ethanol-free pumps(same fuel company). That makes it super convenient in my case.

And it comes back again to how long do you plan to keep the car? If you bought it used, there's no real point in going ethanol-free; the damage might already be done so just save the money on the cheaper fuel. If you bought new and plan to keep it for less than 7 years, save the money since the pump and injectors will almost certainly last that long even on a steady diet of E15. Only consider pure gas if you plan to keep the car for 10 years or more and your annual fuel consumption is relatively low.

Finally, running pure gas is no guarantee you won't eventually have fuel system problems at some point; all it does is alter the probability of it. You're less likely to have a pump failure, or an injector failure, or a failure in the high pressure side of the system, but it could still happen. The other thing you can do to lower the probability a whole lot more than just ethanol-free is to only use Top-Tier labeled fuel from busy gas stations. The better the fuel quality going into your car, the much better your fuel system will survive.

 

Ok Hammersmith- does entering better fuel quality into your car mean to enter the premium type of fuel, say with Shell, or something else?

 

Difference is, the system in Prius is designed to prevent water entry.

 

Difference is, the system in Prius is designed to prevent water entry.

 

The car systems of cars sold in the US have been hardened against E10 for literal decades now. My 2016 Camry was safe to use E15 according to Toyota.

Ethanol is corrosive to aluminum. What protects those fuel system parts for it is...

water

Some northern Europe countries sold hydrous E15 for that reason.

Flexfuel systems use stainless steel for parts. This is likely the case with regards to lower ethanol blends. Water in fuel was always a concern. Fuel dryer additives have been around before E10 was prevalent, and they are alcohols.

There is already water in the gas station tanks. They don't stop deliveries for the rain. The water content gas also tends to have salts and be acidic. This is known by the engineers making car fuel systems.

 

Single most important thing: overall fuel quality. Best way to get it: look for stations with the Top Tier logo on their pumps. This is a voluntary program created by a group of automakers(inc. Toyota) to set standards for desired levels of additives and minimum levels of impurities in the fuel. Beyond looking at the pumps themselves, you can go to toptiergas.com to find a list of distributors/stations that follow the standards.

Way, way, way down in importance from overall fuel quality is ethanol vs. ethanol-free. I'm not trying to convince anyone to avoid ethanol. In fact, I think E10-E15 is a better choice for the vast majority of people.

So what would I consider triggers for using ethanol-free? (this is just my opinion)
- The only gas stations you have access to have old tanks or low fuel turnover.
- You use the ICE very infrequently, so fuel may sit in your tank for months before it's burned.
- You live in an area of extreme cold(<0F/-18C is not uncommon during the winter).
- You live in an area of extreme temperature swings(50 degree F or 30 degree C swings within 12 hours are not uncommon).
- You plan to keep your car for more than 10 years and more than 150k mi/250k km.

If you meet at least three of the above, I would consider looking for ethanol-free options.


And at the very bottom of the consideration chain is octane levels. There should be no functional or quality difference between the different octane grades from the same station in a Prius. As far as a Prius is concerned(to the best of our knowledge), 87/89/91/93 are all the same. Don't waste money on higher octane fuels unless they're your only option.