Re: Ethanol in Gasoline ( a little long) (archive)

A larger concern should be the natural rubber components that BMW used through-out your fuel system. You may recall a few years back the semi-popular gasohol which was blended to save oil while promoting corn growers an energy taxbreak; this prompted some manufacturers (including BMW, Mercedes and Porsche)to recommend against its use as they all used extensively natural rubber elastomerics in their fuel systems. These compounds tend to swell in contact with alcohols (ethanol) when compounded to about 9% by volume or more.

Gasohol was so labeled only when compounded at 10% by volume or more, and many gas companies then began using ethanol (and to a much smaller percentage, methanol too)to raise the octane rating. Octane rating is determined by the fuel's burn rate in a controlled test (SAE in the US)in an old Oldsmobile engine (no joke)and can be manipulated by additives - the slower the burn the higher the octane (because in that engine, the slow burn provides more expansive combustion, hence used fuel per volume of air-fuel mixture).

Anyway, alcohols may not be such a healthy thing in your gas, depending on the elastomerics in your fuel system. BTW, BMW and Merc have since revised their elastomerics somewhat, since in the US, both ethanol and methanol(a popular "dry gas" additive in the cooler climes) are easily present at lower-than-label (10%) amounts in many mixes around the country. It's interesting to note that many "brands" are often terminal mixed at major storage points through-out the country and only certain point-of-use (e.g. Techtron for Citgo/Amoco)additives are really brand related, or for that matter unique to the gas you buy. Same for non-brands - they're only left overs of major brands off-table at the terminals sold at a discount to rotate the terminal inventories dependent on refinery operations.

As for me and my '92 E31, I'll try to steer clear of alcohol enhanced fuels - EPA says that anything over 4% should be so noted btw.

Roger

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