Moisture problems in unleaded fuel?

D

I live in Tucson, AZ. I'm  also a retired Tucson Firefighter and was a HazMat Tech for the department with a chemistry education.  

Gasoline , if you're using gas with 10% ethanol (E-10), which is pretty common these days, it will accept up to 0.63 ounces of water per gallon at 60° F …

10% ethanol can absorb water up to a certain ratio depending on the ethanol volume. 15% can absorb more water than 10%. In Arizona our ethanol content is usually 6% - 7% with an occasional 8% even though our pumps say up to 10%. If you have any water fall out of your ethanol fuel then it's  saturated and should be drained. If you never see water then don't  worry. It will burn through the engine just like cars, motorcycles or watercraft. I have demonstrated this with a 17 gal. tank on a Flight Design with 4 - 6 oz. of water straight into the tank with our ethanol % blend. The higher the ethanol content the more water the fuel or liquid can hold or suspend. I agree zero water is best. Your vents on the tank doesn't usually allow water entry because of the fuel off gassing and the vent hole is too small to make any difference. Usually water in a tank comes from the pump, poor care with the owner in a gas can or some type of entry from sitting in the rain. 100LL will not absorb water and it sinks to the low point like the gascolator where it could be visible. If you're  going to store the plane for a while or fly at high altitude them some 100LL may be better.

Hi Mike

Rotax allows up to 10% ethanol in the fuel.  Millions of cars and trucks use it also.  I have a 23 year old truck that has never had to sump the tank once because of water.  I leave it sitting sometimes for weeks, no water.  The volume of water you need to have what is called phase separation is very high and unlikely to occur if you fly with any regularity.  Personally forget the magic formulas and just use the correct octane fuel.  

The only time you have to worry is in the spring, April to June.  In these shoulder months the fuel supply is changing from winter blend fuels to summer an you need to worry about high vapor pressure in the winter blend fuels.  Summer blends are fine and that is a lot of the reason fuel is more expensive in the summer.  Winter fuel has a lot of Butane in it to help it vaporize in the colder months.  

The Service Information on fluids is attached.  

Cheers

I’m in the Chicago area and a much bigger fuel problem here and probably most of the country is getting winter blend fuel in May or early June. Winter blend can be sold at the pump until the end of May. Around the first of June on a sunny eighty five degree day I shut down for thirty minutes and was not able to start my engine until I got the plane in the shade with the cowl doors open and waited thirty minutes. 

I have an Edge Performance 912STI engine and use 93 mogas. We have a flight school at our airport with eight planes that have 912ULS engines. They had so much trouble with mogas this spring that they switched to 100% avgas.

Ed

Ed...thank you for that observation, I believe you are correct.  The RVP of winter fuel is very prone to vapor lock and using AVGAS will solve that.  if you can perhaps look for Swift UL94 in your area as it is unleaded and will have the correct octane you need.  Add a bit of Decalin to disperse the lead if you are worried about long term lead buildup in the engine while using the 100LL.

Cheers