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  • Writer's pictureJustin Schaub


Updated: Jul 20, 2022

I am sure at this point you have heard the word ethanol at least if you are of the age of driving. Almost every pump in America has a sticker by it that states the gasoline can have up to 10% ethanol. Have you ever wondered what that means? What does it do? How it affects our cars, especially the older BMWs? Well, let’s dive into this.

Corn is the dominant feedstock of ethanol production.

Ethanol was first used in 1826 but it wasn’t until the 1970s that petroleum-based fuel became expensive and environmental concerns started to evolve. Corn became the dominant feedstock for ethanol production because it was easy to grow, transport, and transform into the fuel-burning alcohol we needed.

In 2005 the USA became the world's largest producer of ethanol fuel, making 15.8 billion gallons. This seems all good and dandy, but cars up to this point were not actually made to run on ethanol blends, including our BMWs. It wasn’t until about 2011 that carmakers started making cars specifically for this kind of fuel including E85, which is 85% ethanol. During the advent of higher-ethanol fuels, we found out it increased the detonation level or the octane. You see at most pumps, 87, 91, or 93 octane, but E85 can produce up to 108 octane. This is great for many reasons, but don’t go filling your E30 with it just yet.

Gasoline containing 10% ethanol

So what is the downside to all this? Well ethanol, especially in lower ratios like E10 (10% ethanol), does not give you the higher octane property of its E85 brother. That being said there are cleaning properties of the E10 mix that start to cause a lot of trouble with these older cars. Ethanol can clean or strip off the varnish and paint in your fuel tanks and degrade your rubber fuel hoses leading to clogs in your fuel filter, lines, or injectors. As stated above, newer cars were designed to be able to handle the harshness of ethanol but our older BMWs not so much. You may actually notice your fuel getting dirtier quicker, the rubber fuel hose cracking and degrading faster, or your engine running rough sooner.

Rubber breakdown from ethanol

So what is the cure to all this? Honestly, the best thing to do is run ethanol-free gasoline, which is still available at most pumps but is more expensive. Since it is not as practical, the best bet is to keep up with preventative maintenance. Just know that the ethanol is breaking down systems in your car. Letting your car sit is even worse as new gasoline is not flushing the system. Change your rubber fuel injection hose once every couple of years, change your fuel filter at least once a year, and try to use good quality gas that isn’t from your local grocery store.

All of these things can help preserve your classic BMW for many years.


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