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Touring Motor Gliders Association (TMGA)

Fuel Discussion for Ximango


Steve Sliwa

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I received this question and thought the group could summarize their advice:

I have a few questions, all fuel related.

Is there a definitive answer to the mogas/100LL conundrum for the Ximango? Rotax (and all the local Rotax owners I know) say that mogas is perfectly OK, yet mogas is not recommended for the Ximango. I'm not concerned about the cost difference, but I am concerned about the build-up of lead by-products in the engine. Is there something else in the Ximango which will not tolerate ethanol (all California mogas has up to 10% ethanol)? Can fuel additives (TCP, Decalin, Marvel Mystery Oil, etc.) be used with 100LL in the Ximango?

An acquaintance who runs the Ximango operation in England did say that if 100LL is used, change the oil every 25 hours and the filter every 50 hours. My 16-year-old Ximango has less than 500 engine hours, so I want to get this right.

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I received this question and thought the group could summarize their advice:

I have a few questions, all fuel related.

Is there a definitive answer to the mogas/100LL conundrum for the Ximango? Rotax (and all the local Rotax owners I know) say that mogas is perfectly OK, yet mogas is not recommended for the Ximango. I'm not concerned about the cost difference, but I am concerned about the build-up of lead by-products in the engine. Is there something else in the Ximango which will not tolerate ethanol (all California mogas has up to 10% ethanol)? Can fuel additives (TCP, Decalin, Marvel Mystery Oil, etc.) be used with 100LL in the Ximango?

An acquaintance who runs the Ximango operation in England did say that if 100LL is used, change the oil every 25 hours and the filter every 50 hours. My 16-year-old Ximango has less than 500 engine hours, so I want to get this right.

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They way I sorted the advice is as follows:

  • Ethanol: the engine is fine but the issue are the airframe gaskets and fittings that might erode in the presences of ethanol. Therefore ethanol above 5% is to be avoided.

  • Mogas: Generally finding high octane low ethanol fuel can be a challenge in some locations. However, I am told that there are racing fuel distributors that stock such fuel. Getting it and transporting it can be an issue. I am planning to get a portable tank and plan to go in this direction for my local use.

  • Additives for 100LL: Additives seem to work for what I have read and I use them when I can. I am currently using TCP.

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They way I sorted the advice is as follows:

  • Ethanol: the engine is fine but the issue are the airframe gaskets and fittings that might erode in the presences of ethanol. Therefore ethanol above 5% is to be avoided.

  • Mogas: Generally finding high octane low ethanol fuel can be a challenge in some locations. However, I am told that there are racing fuel distributors that stock such fuel. Getting it and transporting it can be an issue. I am planning to get a portable tank and plan to go in this direction for my local use.

  • Additives for 100LL: Additives seem to work for what I have read and I use them when I can. I am currently using TCP.

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BTW ... there is lots of data on this website regarding this topic.

Go to the Knowledgebase and type an interesting related search term: mogas -or- ethanol -or- 100LL

You will get lists of various threads and articles stored on the Knowledgebase on these topics.

Here is an interesting article stored in the downloads/files section: link

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BTW ... there is lots of data on this website regarding this topic.

Go to the Knowledgebase and type an interesting related search term: mogas -or- ethanol -or- 100LL

You will get lists of various threads and articles stored on the Knowledgebase on these topics.

Here is an interesting article stored in the downloads/files section: link

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  • 2 months later...

There are other issues with ethanol laced gasoline used in aircraft not mentioned above. Ethanol absorbs water. That's how the ethanol testers the EAA sells work. You put a predetermined amount of water in the test tube and add a predetermined sample of your gasoline. There are graduations on the tube so you can get the mixture right. Then, you shake it up and let it sit for about 5 minutes. If the water disappears, ethanol is present. If all the water separates from the gasoline (i.e., back to the original mixture) there is no ethanol present. If it's somewhere in between there is some ethanol present. So, when ethanol is in your fuel and you sump your tank and gascolator it won't show if there is water in the fuel up to or equal to the amount of ethanol in the fuel. If you have more water than ethanol in the fuel the water amount above the ethanol level will show. This possibility of hidden water in the fuel raises the risk this undetected water can freeze in the lines at altitude, although the ethanol will lower the freezing point somewhat below 32F. Ethanol by itself in gasoline (without water) can also cause severe vapor lock if it gets to the right temp inside the line under your cowl. This usually only happens if the fuel line runs above or near the muffler (sometimes unavoidable), or if you have serious overheating issues with your engine. I have seen it happen with certain Rotax installations, though.

Another thing to watch out for, not necessarily with the later model Ximango's because of the aluminum fuel tanks, but rather with other motorgliders that have fiberglass fuel tanks, is ethanol attacks epoxy resin. It will also attack polyester resin, but you don't see much polyester used in aircraft construction. Polyester is generally limited to boat construction. If the inside of fiberglass fuel tanks aren't coated with an ethanol barrier it will cause the resin to soften, often distorting wings where wing tanks are located. Some rotomolded plastic tanks are also subject to ethanol issues if they're not coated to resist ethanol. I saw a set of Sinus wings (fiberglass tanks) at Sebring a couple of years ago that were headed back to the factory for repair after severe ethanol damage. There were big (basketball sized) concave dents in the wing skins where the fuel tanks are located. Since the wing tanks sit against the spar I was curious whether it had softened the spar, too, but I never got a straight answer when I inquired.

Here in Tennessee there are quite a few stations that offer ethanol free UL93. I primarily run Sunoco UL93 in my X, but more stations are coming on line all the time with ethanol free gas as people realize E-10 is a waste of money because of all the ethanol issues and the fact that there just isn't as much "bang" as straight gasoline. I checked the mileage once in my Subaru and it gets 18% lower gas mileage with E-10 versus UL87, but E-10 only costs about 8% less. So, running ethanol free in your car is a no-brainer if you can find it.

I can also get UL110 racing fuel, but I have not run it.

If I have a choice between 100LL and E-10, I run 100LL. I run a semi-synthetic oil in the engine that has lead scavenging properties. So, if I'm out and about I can run up to 50% total usage of 100LL without having to worry about using TCP or one of the other lead scavenging products, provided I do oil changes on about a 25 hour schedule (filter and oil at 50 hours) and wipe the lead residue out ofthe oil tank. If I have a choice between 100LL and ethanol free UL93, I run the UL93. UL93 is what the Rotax beastie really wants for dinner.

Edited by Thermalseeker
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There are other issues with ethanol laced gasoline used in aircraft not mentioned above. Ethanol absorbs water. That's how the ethanol testers the EAA sells work. You put a predetermined amount of water in the test tube and add a predetermined sample of your gasoline. There are graduations on the tube so you can get the mixture right. Then, you shake it up and let it sit for about 5 minutes. If the water disappears, ethanol is present. If all the water separates from the gasoline (i.e., back to the original mixture) there is no ethanol present. If it's somewhere in between there is some ethanol present. So, when ethanol is in your fuel and you sump your tank and gascolator it won't show if there is water in the fuel up to or equal to the amount of ethanol in the fuel. If you have more water than ethanol in the fuel the water amount above the ethanol level will show. This possibility of hidden water in the fuel raises the risk this undetected water can freeze in the lines at altitude, although the ethanol will lower the freezing point somewhat below 32F. Ethanol by itself in gasoline (without water) can also cause severe vapor lock if it gets to the right temp inside the line under your cowl. This usually only happens if the fuel line runs above or near the muffler (sometimes unavoidable), or if you have serious overheating issues with your engine. I have seen it happen with certain Rotax installations, though.

Another thing to watch out for, not necessarily with the later model Ximango's because of the aluminum fuel tanks, but rather with other motorgliders that have fiberglass fuel tanks, is ethanol attacks epoxy resin. It will also attack polyester resin, but you don't see much polyester used in aircraft construction. Polyester is generally limited to boat construction. If the inside of fiberglass fuel tanks aren't coated with an ethanol barrier it will cause the resin to soften, often distorting wings where wing tanks are located. Some rotomolded plastic tanks are also subject to ethanol issues if they're not coated to resist ethanol. I saw a set of Sinus wings (fiberglass tanks) at Sebring a couple of years ago that were headed back to the factory for repair after severe ethanol damage. There were big (basketball sized) concave dents in the wing skins where the fuel tanks are located. Since the wing tanks sit against the spar I was curious whether it had softened the spar, too, but I never got a straight answer when I inquired.

Here in Tennessee there are quite a few stations that offer ethanol free UL93. I primarily run Sunoco UL93 in my X, but more stations are coming on line all the time with ethanol free gas as people realize E-10 is a waste of money because of all the ethanol issues and the fact that there just isn't as much "bang" as straight gasoline. I checked the mileage once in my Subaru and it gets 18% lower gas mileage with E-10 versus UL87, but E-10 only costs about 8% less. So, running ethanol free in your car is a no-brainer if you can find it.

I can also get UL110 racing fuel, but I have not run it.

If I have a choice between 100LL and E-10, I run 100LL. I run a semi-synthetic oil in the engine that has lead scavenging properties. So, if I'm out and about I can run up to 50% total usage of 100LL without having to worry about using TCP or one of the other lead scavenging products, provided I do oil changes on about a 25 hour schedule (filter and oil at 50 hours) and wipe the lead residue out ofthe oil tank. If I have a choice between 100LL and ethanol free UL93, I run the UL93. UL93 is what the Rotax beastie really wants for dinner.

Edited by Thermalseeker
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