3500 hours in my 150 since 1987, never a problem with Mogas. Never a carb ice problem in the O-200. I have a carb air temp gauge, and ONLY use carb heat as required to keep the carb air temp out of the “yellow” range during most days. I do not otherwise use carb heat. I flew it in a number of other types under test. Works well in many, but NOT a Piper Tomahawk nor Cessna 185.
The “gum” only occurs if you let the tank evaporate to dry from Mogas. Think of Avgas as one homogenous liquid, like pure water. When it evaporates, it’s all gone. Think of Mogas like a soft drink (soda pop). It is a mixture of many different liquids, each purposefully blended in with for its properties. Mogas loosing its volatility is like the soft drink going “flat” you can still drink it, but it does not get you started as well. Same for the engine. If you leave the glass, and all the liquid evaporates away, you’re left with the coloured sugar – sticky at the bottom of the glass = gum. If you add more soft drink to the glass, it will dissolve the sugar back into the liquid – stirring helps. Mogas is more complex than that, but the principle at the coloured crayon level is the same.
The variability is what has been added to the Mogas. I was told once by experts at an ASTM gasoline standards meeting in San Francisco, that 100,000 gallons of molasses had spoiled, and was unfit for sale. How to get rid of it? blend it off into gasoline, but at a concentration just below the threshold for taking the gasoline off spec. What’s that you ask? Yup, they added sugar to USA Mogas!
Here in Canada, there have also been cases of counterfeit Mogas. The “safety kleen” fluid used in auto repair shops for cleaning the filthy car parts was being filterd, and blended into Mogas, and sold into cars. ESSO got complaints about their gasoline dissolving the plastic fuel system components of cars in a certain geographical area. They secretly went out and bought their own gas back, and analyzed it. Spectographic analysis revealed the culprits. It was big news here for a while. I always buy my Mogas from a reputable seller, 1300 litres at a time, and I test it for alcohol.
Is there a portable test kit for gum (avgas)?
I have looked around and it doesn’t look like it.
It is a mixture of many different liquids,
Just like AVGAS, which is also a mixture of many different hydrocarbons.
Unlike Swift fuel, which is a mixture of two different hydrocarbons.
Here in Canada, there have also been cases of counterfeit Mogas.
Here too. A chap had drums of paint thinners near his Cessna. After an unrelated fatal crash, the authorities investigated. But they couldn’t fault it as a fuel. They even ran it in a test engine and couldn’t tell the difference between thinners and Avgas. Not so good for the paintwork though. There’s an AAIB report here.
I’m not sure about fuel going off. Old Landrovers, sometimes left for months if not years, still start and run perfectly well on what’s in the tank. What kills them is absorbed water in the fuel rotting out the tank bottom. Any gunk in the fuel is dissolved gasket and pipe sealant. There’s one at the back of the shed that hasn’t run for many, many years. Now where did I leave the key….
Any gunk in the fuel is dissolved gasket and pipe sealant
What would need to be in the fuel to dissolve the gaskets/seals?
Petrol. And 60 years.
Edited to say sorry, that was a bit flippant. Actually I have seen 60 year old fuel, but not tried to run on it. It certainly still smells like Petrol. The sealants referred to are modern varieties, only in the Petrol for 20 years. Some swell up into a yellow gelatinous substance. But I do have a car that’s not moved since 1995 and I’m wondering if there is fuel in the tank.
