Gas Mileage As Affected by Gas Quality

When I bought my Prius, the salesman promised it only needed "regular" gas. My last car, an Acrua RSX Type S, said to run on premium, but regular would do in a pinch (or to save $$). I tried using regular but noticed sluggishness & a definite more wimpy tone in my aftermarket exhaust, so went back to hi-test,

However, I had no need/desire to try high test in the Prius. The Prius is what it is.

I could never afford a Mercedes. I just went to visit my older brother, a diehard Volvo fan. He would not belive me that the Prius has the same/as good safety rating with side-curtain airbags. His wife said the Prius seemed to have more room in the back seats than the Volvo.

I have never test ridden a Mercedes. If you can afford a Mercedes and gas mileage does nto break your bank, why get a Prius?

Most sincerely.
Gold Prius

 

FYI - There is a section in the Technical Training literature about the use of higher octane gas:


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The Prius does have a knock sensor, so it can adjust ignition timing (and possibly valve timing) based upon the octane rating, but Toyota doesn't recommend using higher octane gas for the above reason.

 

<div class='quotetop'>QUOTE(marcoinpb @ Aug 29 2007, 03:58 PM) [snapback]504010[/snapback]</div>

My interpretation:

I believe they are talking about starting the ICE - they must have found during testing that using higher octane gas may cause issues with the ICE starting.

The second note is basically reminding the tech that this problem could be more difficult to troubleshoot because the ICE starting and stopping is controlled by the HV ECU; it isn't as obvious that it is a starting problem because the driver does not start the ICE directly.

I am not doubting your empirical observations; just providing some info that I ran across with regard to octane rating.

I think it may be possible that your high test gas may have better energy content than the regular octane gas. But that is not necessarily due to the higher octane rating. The regular graded gas may use more ethanol, for example, which would lower the energy content.

 

I just started putting Premium in my car. I always used regular. But about two months ago when the cost of regular was the same cost as Premium normally, I told Prius "Look, if gas prices go down and equal the cost as to what I'm paying for regular, I'll get you high quality juice." Which is now. I haven't noticed yet any sort of higher milage. I'll have to keep better track of it.

 

Putting gas that has a higher octane than 87 in the Prius is a waste of money, pure and simple. You're probably not going to cause any damage to the car by doing it, but the idea that you're "treating" your car by putting higher octane gas in has no basis in reality.

Now, I think there's at least a debate that can be had about the so-called "Top Tier" gas, but you are throwing money away if you put higher octane gas in your Prius.

 

<div class='quotetop'>QUOTE(Betelgeuse @ Aug 30 2007, 12:23 PM) [snapback]504335[/snapback]</div>

Amen

 

<div class='quotetop'>QUOTE(marcoinpb @ Aug 30 2007, 11:51 AM) [snapback]504418[/snapback]</div>

You did ask for comments in your OP. Unfortunately, the comments don't seem to be in agreement with your desire to use higher octane fuel. My opinion is that you should use whatever makes you happy, but understand that it isn't recommended by Toyota.

The facts that I can offer:

1. The owners manual specifies that you should use 87 Octane fuel for a US spec Prius.

2. The technical training literature also suggests that you use 87 Octane fuel, and they also specify a reason why they make this recommendation; they believe that use of higher octane fuel may cause problems with starting the engine and this may be particularly troublesome for the Prius because the ICE will start multiple times during each driving cycle.

Speculation that I can add:

There is at least one thread where a Prius owner had an unexplained "no-start" condition while driving on a freeway. That owner was using Shell V-Power (91 Octane) fuel at the previous fill. Maybe the gas was the cause?

http://priuschat.com/index.php?showtopic=33881

 

<div class='quotetop'>QUOTE(marcoinpb @ Aug 30 2007, 01:51 PM) [snapback]504418[/snapback]</div>

There's a decent short description on a page belonging to the American Chemical Society here, but there are lots of other descriptions elsewhere of this same issue. Basically, all higher octane gas does is resist explosion until the engine gets to higher pressure. If you ever experience premature explosions in your engine (i.e. "knocking"), sometimes switching to a higher octane will help address that problem. However, as long as your engine is running well in your Prius, there is absolutely no benefit to be gained by running the higher octane gas; since the engine never gets to the compression levels where higher octane gas makes a difference, there is nothing gained by having that higher octane gas in the car.

I hope this makes sense and helps you to understand the point we were trying to make.

 

<div class='quotetop'>QUOTE(marcoinpb @ Aug 30 2007, 02:51 PM) [snapback]504418[/snapback]</div>

It's simple

High Octane Gasoline contains less energy than Regular Gasoline (Particularly where Ethanol is the Octane Booster).

High Octane Gasoline combusts more slowly than Regular and can lead to incomplete combustion in an engine designed for Regular.

Incomplete Combustion further decreases the amount of energy available per unit of Gasoline.

Incomplete Combustion can also lead to excess unburned hyrdocarbons in the exhaust which can, at best increase pollution, gum up parts, and throw emissions errors, and at worst destroy the emissions system.

Simply put, there is no way, according to the laws of physics, that High Octane Gasoline can provide any perfomance improvement in an engine designed for Regular, and it can be harmful in multiple ways.

High Performance Engines are generally programmed to adapt to lower octane but not vice versa.

If your Engine designed for Regular Fuel is requiring higher octane, there is a problem with the engine tune.

Here's a Link

Gasoline FAQ - Part 3 of 4[

6.16 What happens if I use the wrong octane fuel?

If you use a fuel with an octane rating below the requirement of the engine,
the management system may move the engine settings into an area of less
efficient combustion, resulting in reduced power and reduced fuel economy.
You will be losing both money and driveability. If you use a fuel with an
octane rating higher than what the engine can use, you are just wasting
money by paying for octane that you can not utilise.

Or, to quote another source (Wikipedia, for what that's worth):

The power output of an engine depends on the energy content of its fuel, and this bears no simple relationship to the octane rating. A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is false—engines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octane rating is minimal or even imaginary.

That's the Facts