What grade of gas do you pump?

Wow... I sure don't want that kind of mechanic working on my car if they don't even know anything about what kind of octane gas to put in the car. My last car demanded 91 (2k3 Sentra Spec-V). I could put in lower octane, but then the anti-knock sensor would turn down the timing and I'd get crappy performance. I'm glad the Prius uses regular gas. I fill up half as much and pay around 40-50 cents less per gallon.

 

It may be that he uses premium gas gas not for the higher octane but for the added detergent. Several gas companies tout their premium as purer and having enhaced detergent content. If you use a Top Tier brand you can get the benefit of the extra cleaners without having to buy the more expensive premium grade.

 

A higher grade of ocatane simply allows higher compression before combustion. Fast cars need a high octane rating because of their piston's large compression ratio. For example, an octane rating of 93 would mean the other 7 percent mix would be hectane. If there was a higher percentage mix of hectane in the fuel, it would ignite prematurely in the cylinder heads during compression (called "knocking") and cause damage.

Hectane, the 13% grade you find mixed with an octane rating of 87 is all that is needed for any conventional car (including the Prius) to prevent premature ignition. Having a higher grade of octane in the Prius does not give any sort of benefit to the longitivity of the engine or boost power/increase mileage. The only thing it does is take more money out of your pocket.

 

It is less explosive under compression but the spark plugs are the only thing that ignites the fuel in a petrol-powered motor (and if it isn't you're in trouble).

Gas mileage will have zero effect whether it is 87 or any other higher grade.

 

I use 87 octane in my Prius, Honda Accord, 1988 Ford mini van, and 93 in my Harley. HD calls for at least 91 in the 1200 CC engine.

 

I can't say if it is bad for the emissions system, but it will pollute more, as the octane additives do not burn as well as the gasoline. Might not be measurable, but it IS more pollution.

In CA, the same detergents must be used in all grades of gasoline sold (we had a lawsuit about that maybe eight years ago) - so at least here in CA, there's ZERO reason to use a higher-grade gas than one that does not ping. If the car doesn't ping on the lowest octane, the lowest octane is what you should use.

 

Can someone confirm that the same degertents must be used in all grades of gas in California? Perhaps via a link to the lawsuit, because Shell claims that the V-Power is only in the Premium and I am hewre in California.

 

compression ration of 13 to 1 only occures under very light load where as the high load is at 8 to 1 so only low octane is need to control detonation. Also the 1NZ-FXE engine is equipped with a knock sensor that will retard the timing if need to control any detonation that it hears.

 

galaxee,

I pick up my 2006 Red Barcelona Prius Monday after waiting for almost 7 months.

I downloaded a 2004 manual from a generous PriusChat member just last week and have been reading through it. Just last night under "Gas" (I don't remember what page because it printed out 318 pages, but about page 190 under my print out) it says specifically to use "octane 87 or R.O.N. 93, or 'higher'". I don't know what they meant by R.O.N. 93.

I have been concerned on this matter because I went to 4 local gas stations and all have regular at 89 octane (Shell, Phillips 66, Citgo & Hucks). All are close to me. I did find a BP with octane 87 but I rarely go there because they are not listed as "Top Tier" and are not open all night, nor are they conviently located and I usual fill up after work (2nd shift).

Everything I had read and searched for prior to this on PriusChat since becoming a member about 3 weeks ago said Octance 87 and so does "john1017a's site". Does anyone know if the 2006 Manual recommend Octane 87 or "higher"?

Thanks!

joe

 

Hmm. I'll take a look. It was Unocal that got spanked on this at the time... and I know that all of *their* stuff has the same detergents.

Good to be skeptical! Maybe it was ONLY Unocal? I'll poke around. I had a friend involved in the lawsuit.

Anybody know what "V-Power" actually is? if it is just a marketing slogan, then they may very well only offer it in the "premium" grade.

 

Don't have the time to read through this to see if it is relevant (likely not?), but it has something to do with Unocal and what they claimed about their gasoline.

http://www.ftc.gov/os/adjpro/d9305/031029r...stopexhib08.pdf

 

Motor Octane Number (MON) and the Research Octane Number (RON).

MON is a measure of performance of the fuel at high speeds or under heavy loads, while RON repersents the performance during low speed conditions. The octane number displayed at the pump is the average of these two values ([R+M]/2).

 

Hmm... as I understand it, the higher the octane, the less explosive. The sparkplug fires, and the lower octane will hit the pistons hard, expending most of its push before the piston drops far. The higher octane will not hit so hard, and be pushing the piston harder as it goes farther from the head than the lower octane. Theroritcally, pistons pushed will give the engine more torque than pistons that struck.

Cars that I have owned with low compression engines, did no better with higher octane. The one car that I did own that had a high compression engine, did do better with high octane.

 

Humm.. I believe the prius has a high compression ratio... what is it?... 12:1 or so?
Yet I've heard it does not better.... of course the atkinson engine is a whole different animal.

 

i see our 05 manual also uses the "or higher" term.

i'd just get the lowest octane level that's conveniently available if i were you. are you at high altitude? iirc, the octane levels differ at high altitude.

 

I like filling up with Premium. Nothing beats a V8 with a 30 gallon tank of Premium Gasoline. B)

 

I understand that you're trying to be a troll, but I don't even know what this is supposed to mean. . .

 

The only places I see 85 octane sold are at high elevations. That's what I use while driving there. Otherwise 87.

 

13:1

 

OK, so this is going to get geeky for a moment, so please bear with me.

Although Toyota does state in their documentation that the compression ration is 13:1, the valves are held open well past the point where they would close on a normal Otto cycle engine so the net result is that you actually only get 8.0:1 compression ratio (which is also decumented by Toyota). The head design is the same as other Toyotas, its the VVTi engine control program that performs that little timing trick, which converts the engine from Otto cycle into an Atkinson cycle engine. The expansion ratio does stay at 13:1 which is where the efficiency comes in.

As for which gas to use, the correct answer is 87 octane. Not only is it the grade that was designed for the engine, the rule of thumb for gasoline is that the higher the octane rating the lower the energy in the fuel, but it will have higher resistance to detonation (pinging, etc.) In the old days, it was common practice to buy "higher" grades of gas because it was mistakenly thought to be better since it didn't ping in the super high compression ratio engines of the day.

The reality is that you will get the most power and fuel economy with the lowest rating that does not cause pinging. If you want the "best" gas then go with quality of manufacturer (in my case that means going with 87 Chevron).

As for the detergent question, typically most gasoline has some sort of "package" in it containg detergents and possibly other ingredients. having been a former exotic car owner, I got together with a few other engineers and coaxed one of then to investigate this situation for us. The result was that Chevron was found to always have some sort of detergent package in all their products. Their package (Techron/ProGuard) is also sold in bottles which really did help clean up some of the higher mileage cars that had been run on Shell and other brands (whose packages were not able to keep the fuel systems relatively clean).
http://www.chevron.com/products/prodserv/n...nt/fueladd.shtm

Geek off.

I hope that clarifies these questions, and yes I used to be a mechanic and am now a Ph.D level Prius owning engineer.