I have a 2001 M-5, the only gasoline I can get has 10% ethanol. I can see a definite difference with it in my car. Is sea foam additive good for this or can I use something else. PS all I use is premium gas Randy Proffitt in Mobile, Ala
BMW, Porsche, Audi and VW have approved Techron as a fuel additive but I would not suggest over use of it. Some folks add a bottle every 5K-10K to reduce carbon build-up. It probably won't have any influence on the 10% ethanol content in most gas. Seafoam is an online fantasy cure for everything. It's not BMW or any other car maker approved AFAIK, so I'd skip it and use the Techron if you are looking for a safe, effective approved fuel system/carbon deposit cleaner. Techron is a Cheron oil product detrergent additive used in their fuels as well and is available from many mail order and some local suppliers. BMW sells it in their own bottle with the BMW brand on it.
Seafoam is good for cleaning up a cruddy fuel system (like carbs or injectors), not for octane or mileage boosting. The simple fact is that ethanol doesn't have the same energy output as gasoline, so your mileage will be somewhat lower. The only way around that is to use something that completely compensates for the ethanol. Something like 110 octane avgas. I seriously doubt it's worth the bother or the cost to do that. Just drive your car. There's nothing wrong with it.
The energy content of gas is pretty consistent regardless of octane. Octane rating has nothing to do with the energy content per say and typically makes no difference in engine performance other than to prevent detonation. Oxygenated gas provides a slight power increase, but not much. 10% ethanol doesn't lower power much as the quantity is so low by volume, it's a very small change. MPG and driveability issues can change a bit with ethanol and that's why it's undersirable if you have a choice. BTW, Avgas should never be used for auto applications as it's intended for high altitude operation at steady engine speeds and some Avgas still has lead in it.
