Folks,

I'm running mid-grade in my 2009 STi for day-to-day use, and use either Premium or Ultra 94 for track events. However, I'm interested in what you prefer. Here's a little primer as a context to start though.

Aside from Sunoco, the industry has standardized around E10 (10%) for Regular, no Ethanol for Premium, and since Midgrade is a blended, it becomes E5. This means that when you fill with Premium, you are NOT getting Ethanol.

Ethanol is actually good for fuel systems, as it helps clean and remove water. All Sunoco fuels have Ethanol, including the coveted Ultra 94.

Cleaning Properties

Initial use of Ethanol fuels tends to clean engine residue and this ends up in filters. Gas stations had this same issue upon conversion, but this happened in 2006 in the key urban areas, so it's behind us for the most part.

This is not an issue for new engines or storage systems, and the good news is engines are cleaner as a result.

No More Water

Ethanol-based fuels (unlike most fuels) are hydroscopic (readily abosorbs moisture). This requires some special procedures in storage and has created some concern when not done adequately.

The consumer concerns that exist are based on Ethanol's sensitivity to water in storage. This is some times referred to as it's 'stability'. There is no issue for engines with nearly undetectable quantities of water dissolved in fuel. Gross amounts of water into storage tanks (from a rare fillbox leak, for example) will stratify the fuel an it will be identified by daily operational checks, and in that event the fuel will need to be replaced.

On the positive side of things, there will be no water in your tank if you occasionally run Ethanol fuels, as tank vapour space moisture gets consumed with the fuel in normal operation.

Customer Preferences

General preferences I hear about are to avoid Ethanol for marine and small engine appications. Marinas have a greater exposure to water and often were not as knowlegable about the properties of Ethanol when it was introduced, and it caused concern. They also have a winter storage cycle that is unique, but this does not need to impact preferences, as Ethanol has the same stability of other fuels, stored properly (shelf life of many years).

That being said, I'm interested in your preferences.

What are you running?