Date: Fri, 11 Mar 2011 09:48:50 -0600
Reply-To: mcneely4@COX.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dave Mcneely <mcneely4@COX.NET>
Subject: Re: gasoline was STP Gas Treatment
Content-Type: text/plain; charset=utf-8
---- DW <dcwilton@gmail.com> wrote:
> Dave:
>
> I have looked for a good reason not to run premium gasoline, but I can't
> seem to find any detailed information. I have always gone by the sticker on
> my van that states something about a minimum octane rating of 91. Based on
> your post I did manage to find a website with an excellent database of gas
> stations selling ethanol free gasoline (http://pure-gas.org/). Can you
> expand on the reasons why my van will be/run/last better with a lower octane
> gasoline? The manual I have for my '91 Multivan specifically states that
> ethanol is a no-no, but I assumed that I couldn't buy anything but blended
> gas in WA.
>
> Thanks,
First, the 91 octane recommended in the book is Research Octane Rating. The number posted on the pump in the U.S. is the Anti-Knock Index. An 87 anti-knock index is equivalent to 91 research octane rating:
http://en.wikipedia.org/wiki/Octane_rating
The waterboxer is built to tolerances for which this 87 rating is ok. So long as it does not knock on the fuel used, that fuel is ok. If it knocks, use a higher octane fuel or switch brands. Maybe the stated octane on the fuel is incorrect. But in general, only high compression engines benefit from higher anti-knock indexes than 87. Recently, owner's manuals for vehicles make that specific point, that using a higher index fuel than specified is of no benefit. It is not helping the engine any, just helping the fuel vendor's profit margin at the expense of one's pocket book. The anti-knock index has nothing to do with injector cleanliness or any other property of running except knock.
I used to be confused somewhat by the lower anti-knock index fuels that are commonly sold at higher altitudes. Above 3K feet in the western U.S., indexes as low as 85 are common. When there, I would buy "premium" fuel. This lower index fuel is offered because of a combination of the lower air pressure at elevation (thus lower compression ratio in the combustion chamber), and lower oxygen availability in the air, meaning slower burning of fuel; knock is less of a problem, and lower index is ok. After using a few tanks of 85 octane fuel when out west, specifically in Nevada at a couple of remote areas where only regular 85 octane was sold, and experiencing no knock, I no longer pay for premium fuel when out there. I just use whatever is sold as regular unleaded.
The previous paragraph is my understanding of what is going on. Someone who is more expert on the physics and chemistry of the internal combustion engine than I am may have a different take, but the bottom line is that premium fuel is a waste of money and ultimately a waste of oil, because it takes a little more oil to make a given volume of it than it does the lower octane stuff.
In Oklahoma, ethanol free fuel is commonly available, but costs more than that with ethanol. In a lot of the country, only fuel with alcohol is available. At home, I use ethanol free fuel for both engine considerations, and for not encouraging farmers to switch from growing food to growing fuel. Generally, when on the road, I buy whatever is conveniently available, and have not perceived any problem with the engine running ok. Mileage suffers. Whether any seals or other components of the fuel delivery system are being harmed, I can't tell so far. In some places I would have to search all over a big city, or risk running out of fuel when on the road. I understand that because of the hygroscopic properties of ethanol (the reason that for general use, ie. non-analytical and other non-critical use in a laboratory, alcohol is usually sold as 95% rather than absolute, and absolute is considered not to be so once opened), gasoline with it is more likely to contain some water, also. But, we can only do so much to counter the problems the "system" throws our way.
Now we hear that the vendors will be allowed to go to 15% ethanol.
mcneely
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