Sunoco Tech: Octane Stability Article
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From: US-PNW
Sunoco Tech: Octane Stability Article
Interesting and in simple language, this article talks about how a gasoline formulation's octane rating is affected by storage.
https://petroleumservicecompany.com/...-octane-fuels/
For those pre-'70 cars with vented gas caps, this:
So, unless you are driving your car in cold temps where refueling with a "winter" blend gets used before spring temps hit, attempt to fill the tank with "summer" blend prior to storage. (I'm unsure how sealed the fuel system is after '69 in this regard - but the gas caps are non-vented.)
https://petroleumservicecompany.com/...-octane-fuels/
87 octane fuels tend to be less refined and contain more unstable hydrocarbons. As the months pass during storage these unstable components react to form gums, varnishes and lower octane hydrocarbons. As a result the octane can decrease within months for 87 octane fuels, especially when stored under less than ideal conditions. 93 octane fuels are more refined and contain more stable hydrocarbons. These stable hydrocarbons can last 2-3 times longer than 87 octane fuel. Even in proper storage 87 octane gas can start to degrade in 3 months, 93 octane fuel should last closer to 9 months before degradation is noticeable. Keep in mind that 93 octane fuels are still susceptible to octane loss and vapor pressure decreases due to butane evaporation.
Butane has a high blending octane value which helps manufacturers hit their octane targets. The main downfall of butane is that it boils at 32°F. If the fuel tank is vented to atmosphere the butane can start to evaporate out unless the daily temperatures are below freezing. This makes cold weather fuel more susceptible to vapor pressure loss and octane decreases.
