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Ethanol In Your ROTAX Aircraft Engine: The 2 and 4 Stroke Killer

Updated: Jan 13, 2023

This article was published as a post on the UPAC Facebook page by Chris Tregunno and is being copied below with author's permission.

This post is for informational purposes only.


Note: This post may contain affiliate links. This means we may earn commissions if you make a purchase using these links, at no cost to you.



Effects of Ethanol In Your Aircraft Fuel System

Nowadays ethanol in fuel is everywhere. I am not going into the why, rather the cause and effect of its use, how to avoid it for aircraft MOGAS use, and where to get non-ethanol fuel.

The gas you pump at gas stations contains a blend of ethanol and gasoline plus a multitude of different additives that are in it. From my experience while working at ESSO refinery in Nanticoke Ontario, the ethanol and additives are “blended” at the last stage of fuel production at the point of dispensing. The trucks receive gas and a blend that is specific to each consumer companies requirements and specifications at that point. Ie: Pioneer, Petra Canada and Shell all have there own special blends. And this is accomplished when they are loaded at the refinery terminal before heading out to your favorite gas station.

Identifying ethanol at the pump can be by the E number. It indicates the percentage of blend. For example, E10 contains 90% gasoline and 10% ethanol . In modern Cars and trucks used today, the engine computer and fuel systems are designed to adjust the ignition timing to accommodate the different fuels used. One day you could fill up with 97 octane, and the next you fill up with 91, yet your car still runs fine and no harm comes to components and it still runs reliably . In aircraft however you could cause irreparable harm to your engine, and it could harm you your aircraft or even worse, cost you your life.

And here is why.

The effects of ethanol use are:

  1. Ethanol will start to absorbed water over time, and it can absorb up to 50 times more water than pure gasoline! This is a bad idea when you want to avoid carb icing.

  2. Ethanol in itself, is an excellent solvent. That means that putting ethanol blended gasoline in your airplane’s fuel system could cause damage. The fiberglass gas tanks will break down over time and will clog up your fuel filter and start to degrade the fuel tank itself, not to mention the rubber hoses and o-rings in your fuel system too boot. Either way it’s costly, and could cause engine stoppage while in flight or worse on takeoff. Regardless if it is a 2-stroke or not. If you buy a used airplane, I strongly suggest you ask the previous owner where he got his fuel, looks at all the filters and inspect the fuel tank and system for previous damage. It very well could be the previous owner had no idea if it contained ethanol in he or she simply assumed that the fuel was good.

  3. Lastly, and this is a big one, the 2 stoke killer is that while ethanol blended gasoline is stored in your airplane’s fuel tanks, it will start to separate from the gasoline over time. The 2 stroke oil remains bonded to the gasoline but not the ethanol. Therefore the result will be that the water part and ethanol part remain bonded and there is no oil for lubrication for your engine. This will result in a engine parts damage and or failure while running. Again really really bad when your flying!!

How do you test for Ethanol and additives?

What’s needed;

Mason jar with lid Non-permanent marker ✅ Water ✅ Gasoline you are going to test

Method :

1. First take your mason jar and fill it with approximately 100 ml of water. 2. Mark with your non-permanent marker the top of where the water is on the jar 3. Fill jar approximately ¾ of the way up with the gas you are going to test and cap the lid firmly closed. 4. Shake jar for approximately 5 seconds 5. Put on flat surface and let settle (approximately 1 min ) (figure 4) 6. Look at the line on your jar that you put on with your non-permanent marker and note if the water is actually higher than the line you drew on. If it is, that is all additives and ethanol.

List of gas stations that sell ethanol-free fuel

  • All of Canada; Shell v-Power, Canadian Tire 91, ESSO 91

  • Atlantic Canada: Irving Fuels Premium

  • Western Canada: Co-op Premium

  • Ontario: Costco 91

  • Newfoundland, Nova Scotia, & PEI : All unleaded gasoline

*NOTE* 1. the list of gas stations across Canada was obtained from 2. In no way have I personally verified the information provided. I would strongly suggest testing this fuel yourself and also getting proper documentation from the station or companies if your still not certain on its quality. I am not responsible for any liability, incidents, accidents, or damage that could occur because of the information provided. This is merely a guide.


The original Facebook post can be found here.

On a related topic, Popular Mechanics also posted an article on Ethanol in your fuel.

Fly safe and have fun!

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