Fuelling around with the octane numbers

[C M Smith <cmsmith@domain.elided>]

With knock sensor boost control in my SAAB turbos I can certainly tell when 
octane is not as advertised on the pump. Very occasionally I get a tank of 
really good fuel, with higher octane than the pump states (pump is required 
to be labelled in Canada only as to minimum octane)

  I believe Charlie's right as to low octane fuel being sold, at least in 
Canada I have come across deficient octane many times. Sometimes I think it 
may be due to stale fuel as octane numbers drop as the fuel remains in 
storage (evaporation of volatiles or decomposition of chemicals? who 
knows). However, for a while before one of our Shell stations closed 
forever, I was convinced I was getting mid grade fuel when purchasing 91 at 
the pump. My theory at the time was the station operator was getting the 
fuel delivery guy to fill the premium underground tank with midgrade. At 
that time very few cars required premium but lots of people bought it 
anyway under the illusion it was somehow "better" fuel. (I still laugh when 
I see a SUV owner carefully selecting premium fuel for his low compression 
piece of iron) In that case very few customers would know the difference 
and the "fraud" would never be uncovered. Given the slim margins on fuel 
sales (most of the profit earned by gas stations here is on cigarettes and 
sundries sold in the attached store) the temptation to sell midgrade for a 
5 cents per liter (almost 20 cents a gallon) markup must be well nigh 
impossible to resist.

Just my 5 cents.
Michael Smith
Calgary, Alberta,Canada
91 Alfa 164L
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