Gasoline Information
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Date: Wed, 4 Mar 1998 13:42:36 -0600
From: john_j_harville@amoco.com
Subject: Gasoline.....THE FINAL WORD(S)
To: Toy4X4@tlca.org
OK, thought I would finally get involved with all of the recent talk
about gasoline octane ratings and pressurized fuel tanks. Working for
Amoco, I know a "little" about these things. I'll start with octane.
OCTANE-the first and foremost rule for octane is; only use what your
car NEEDS. This means if your car knocks or pings with 87, then move
up to 89, then to 92. As many have stated, you are indeed wasting your
money with higher octane fuels....unless of course it is needed.
Higher octane ratings mean higher flash point. Which translates to
less pre-detonation that causes ping and/or knock. Usually this is
only required on high performance(read: high compression) engines
where the temps and pressures can easily cause pre-detonation. As far
as keeping your injectors clean, you wasted money for "premium" gas
would be better spent on a can fuel injector cleaner once every 6
months or so. Higher octane gasoline does not clean your engine. The
additives(detergents) in the gasoline are responsible for the
cleaning. Here's where I plug Amoco products--> Seriously though,
Amoco's Ultimate gasoline does go through a proprietary process that
removes the PNA's which are basically poly-nuclear-aromatics. These
are responsible for the slight yellowish color in gasoline and are
ultimately responsible for resid(tar-like) deposits that can
accumulate in your injectors, etc. I am not telling you to run out and
start buying Amoco-Ultimate, just informing you of the product.
GAS TANK PRESSURE- Gasoline and all other hydrocarbons have a chemical
characteristic know as "Reed Vapor Pressure". This can be expressed as
reed vapor pressure RVP or true vapor pressure TVP. They are similar
yet each has it's own calculating method. Anywho....most gasolines
have TVP's in the neighborhood of 9 psig. Which basically means that
all gasolines evaporate until equilibrium(9 psig) is attained. If you
have a cup of gasoline with no lid on it, it will evaporate
"relatively" fast versus a closed or tightly fitted container. As
gasoline is used up in your tank, the void is filled by vapor until
that equilibrium is again met. When you remove your gas cap to fill
up, you are releasing the pressure that was built to achieve
equilibrium. So you see....it has nothing to do with carbonation(no
such thing in hydrocarbons) or oxygenation.
HOPE THIS HELPS CLEAR UP SOME MISCONCEPTIONS
John Harville
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Date: Tue, 2 Jun 1998 03:48:31 -0700 (PDT)
From: Aaron Lung
Subject: Re: Gas to use: my 2 cents
Travis sez:
>I have always used Amoco 93 ultimate. If I use anything lower in octane
>in my 22re after a couple tanks I get knocks especially on long upgrades
>or pulling a trailer.
This is the usual symptom of carbon deposits in your engine.
It's not the only one, but it's probably one of the more common
ones. Hot weather will exacerbate it more. Try a couple of bottles
of Techron or Chevron Progard Cleanup (same stuff, different name)
You WILL notice an improvement. I use it maybe once a year only as
necessary in my '84 22RE. Then go back and use regular 87 and
save some $$.
aaron
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Date: Tue, 2 Jun 1998 03:18:54 -0700 (PDT)
From: Aaron Lung
Subject: Re: Gasoline
Ben sez:
>I was going to tyr Chevron 93 oct today , until i notices that there is
>only one nozzle at the pump. Now it doesn't take a brain surgeon to
>realize that you are not getting pure 93 octane? Anyone know more about
>these types of pumps, that moght can confirm or deny my thoughts?
Believe it or not, octane mixes linearly as far as we
are concerned at the pump. 89 octane is actually an even
mix of 87 and 91 octane, for example. Hence, there's no
point in having 3 different hoses running from 3 different
pumps and tanks these days.
You can also notice more and more Shell tankers drive around
with a huge 2nd tank trailer and tank half the size in front.
I can only surmise the 2nd trailer is full of regular 87
octane stuff, and the small trailer is whatever they mix
in to get the higher octanes. It makes lots of sense.
So, you'll get a hose length's worth of whatever gas the
dude in front of you pumped into his car.
With respect to which octane gas you're using, if the
owner's manual says 87 octane, you're wasting money
pumping anything higher cuz yer engine wasn't designed
to use it, much less know the difference. This is especially
true assuming you don't have knock sensors. 22RE's don't (not on
mine, at least). Of course, you can argue that you can
manually advance your timing more with premium gas to get
more power out of it. FWIW, I run 3degrees beyond factory
spec using 87 octane and still have no problems on my 22RE.
The big brands such as Chevron, Exxon, and Shell passed
BMW's gasoline deposit tests, regardless of octane. Many
other off-brand brands didn't. If you poke around the web,
you should be able to find a gasoline FAQ somewhere giving details
on the test and on how gas works in general. It was posted
to the BMW list several years ago. If I remember correctly,
the test was also published in Consumer Reports several years
back as well.
aaron
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Date: Tue, 2 Jun 1998 03:48:31 -0700 (PDT)
From: Aaron Lung
Subject: Re: Gas to use: my 2 cents
Travis sez:
>I have always used Amoco 93 ultimate. If I use anything lower in octane
>in my 22re after a couple tanks I get knocks especially on long upgrades
>or pulling a trailer.
This is the usual symptom of carbon deposits in your engine.
It's not the only one, but it's probably one of the more common
ones. Hot weather will exacerbate it more. Try a couple of bottles
of Techron or Chevron Progard Cleanup (same stuff, different name)
You WILL notice an improvement. I use it maybe once a year only as
necessary in my '84 22RE. Then go back and use regular 87 and
save some $$.
>Now for some facts some may or may not know. My
>grandfather (mechanic by trade) informed me years ago that everytime you
>move gas ie pump it, that it loses some of its octane rating. Therefore
>if moved several times 93 could really be 89, 90 etc... so if you start
>with 87 you could be getting lower octane then the minimum you need.
I don't see the reasoning behind this...
>Also, the big refiners formulate gas different for the summer months
>then winter months, due to average temperature differences. Their
>surplus is where the cheap guys get their fuel. Therefore in the winter
>they have summer formulated gas and vice versa.
IMHO, I'd favor using summer gas. I usually take a 5-10% decrease
in mileage due to 'winter gas' here in San Jose, CA, where our
deep-freeze winters are rarely colder than 55-60F, and gloves
and down jackets are prominent when it drops to 55F ;-) Did
someone say 'snow'? what's that?
>It is also old gas. So
>you have the wrong formula gas and old gas that's been moved around and
>setting around losing some of its octane rating.
Actually, gas is gas no matter where you get it. The additives are
the differentiator. As long as you get your gas from a name brand
company, you should be fine. But I agree...don't buy gas from some
old run-down shack out in the middle of nowhere...
> Bottom line YOU GET
>WHAT YOU PAY FOR! A few dollars more a week can save hundreds in the
>long term.
True, but a few $$ blown needlessly every week can cost you hundreds
more in the long term also :-)
[I guess that's relative though...the average rate is $1.30-$1.40/gal
for regular around here. I hear it's less than a buck elsewhere
around the nation.]
aaron
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