From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Newsgroups: rec.autos.tech,nz.general
Subject: Re: assessing aromatics in petrol
Date: Mon, 02 Apr 2001 18:05:59 GMT

John Ings <jings@ottawa.com> wrote:
>When I store my summer car over the winter to keep it out of the salt,
>I add a concoction sold by Canadian Tire that claims to keep fuel in
>stored cars from deteriorating. The label doesn't say what this stuff
>is, or how it works. Any ideas what it may be, and how effective it
>is?

Fuels are made from a diverse mixture of chemicals, mainly hydrocarbons,
all with differing stability. The specifications are based on a certain
amount of stability - usually based around 3 - 6 months storage at ambient
temperatures ( except military fuels - which have longer storage stability
requirements ).

There are many methods of improving stability ( remove unstable molecules
such as olefins from the fuel, add antioxidants, radical scavengers, and
other stabilisers to the fuel ). Most of the treatments add a mixture
of compounds that inhibit the gum-forming tendencies of the olefins in
the fuel.

>I have in the past had bad experiences with gas that's been in a tank
>too long. It aquires a rank varnishy smell and engines won't run on
>it.

Yup. The double bonds in the olefin hydrocarbons break and hold hands
or grab oxygen from the air. Those gums don't volatilise easily, and
their rancid, sour smell is associated with " stale gas "

>Do modern airtight gas tanks alleviate this problem to some degree by
>cutting down on evaporation?

Gasoline contains within itself the seeds of its own destruction.
The airtight tank does help reduce the intrusion of oxygen, and
more importantly, prevents the loss of volatiles ( critical for
cold starting of carburetted engines, slighly less so for
some modern fuel injected engines  ).

If you want to be nice to the elastomers in your fuel system,
and not have stale gasoline residues, it's better to talk to the
technical services department of a major oil company in your
region to find out which stability packages are best with their
premium grade ( grade not octane ) fuel. Note that companies
supplying the military usually will have enhanced additive
packages in fuels they supply to the military.

         Bruce Hamilton