The old song: After a long standstill, the motorcycle no longer starts or does not start properly. Diagnosis: carburetor closed, fuel broken. What happened?
Mona Pekarek, Jens Kratschmar
It should affect most motorcyclists: After a long period of rest, the bike will not start properly, sputters around or, in the worst case, will not start at all. Old carburetor models in particular are regularly idle in the spring. But actually every type of mixture preparation is affected. The reason: aging gasoline. This has been a problem since the invention of the internal combustion engine. Gasoline ages very quickly in the tank and loses its ignition quality during a cold start. How long can I leave petrol in the tank? Why Does Gas Go Bad? MOTORCYCLE answers.
Can be kept for several months
Basically, fuel is a product with a limited shelf life, and not just because it is ignited at some point in the combustion chamber. Gasoline stored for too long will spoil sooner or later and start aging as soon as it leaves the refinery. Experts from the industry are certain that petrol can be kept for between two to three months or up to a year without any measurable loss of quality. The main factors in aging are: How much light and ambient air gets to the petrol and whether high temperature fluctuations affect the fuel. The petrol will age faster in an open canister than in a filled and closed canister. The fuel tank on the motorcycle is somewhere between these two storage methods, and what is particularly important is how much air, i.e. how little petrol, is in the tank. But what exactly is happening there?
Aging process: boiling
Gasoline mixed with air ignites very well because it contains a lot of volatile hydrocarbons. These hydrocarbons boil between 30 and 200 degrees Celsius, especially the highly volatile components of gasoline that are important for cold starts. These are also the reason for rapid aging, because over a longer period of time these gaseous molecules gradually escape from the petrol in the tank. It becomes more difficult specifically, and the willingness to ignite decreases, which you usually only notice after the winter break. Basically, the only way to stop the boiling itself is to have cool parking spaces and a full tank to slow it down.
aging process oxidation
One reason why the tank should be filled to the brim with petrol during the winter break is the longer-term process of oxidation. Olefins, unsaturated compounds in fuel, can react with the oxygen in the air. On the one hand, small amounts of corrosive acetic acid can form, on the other hand, polymers – long-chain compounds – are formed that are no longer soluble in the fuel. This resinous sludge can clog pumps, lines or injectors. Carburetor drivers can tell a thing or two about the dark yellow finish, and restorers know this annoying phenomenon as gum build-up. Note: The more air in the tank, the higher the risk of oxidation.
Aging process: ethanol
Before the regulars’ table sounds: E10. This is devil stuff! Please keep breathing. Gasoline with a percentage of ethanol – E5, E10, E85 – does not age faster the more ethanol it contains. In fact, the processes already mentioned run a little slower. The alcohol in gasoline causes another deterioration in the quality of the fuel because it draws moisture from the surrounding air. As soon as the alcohol is saturated with water, the gasoline, alcohol and water separate, which can lead to damage to metals and pipes depending on the tank design. The same applies to ethanol fuels: the less air in the tank, the less water the alcohol can bind. On the one hand due to the large differences in volume, on the other hand due to the small surface area on which air and petrol come into contact.
Which gasoline to fill up for the winter?
So what’s in the tank when it’s time for the winter break or another break? It is best to keep the tank full to keep the air away from the petrol. Furthermore, fuels completely without ethanol would be the best choice to prevent water binding, i.e. premium fuels. If you don’t want that, experts advise you to fill up with E5. Although E10 binds more water when stored for a long time before it separates, the water should be kept out of the tank as far as possible. Bottom line: Gasoline in a full tank ages slower than less gas. A completely drained fuel tank can also be a solution. However: The empty tank favors all three processes in the remaining parts of the fuel system, which can have even more serious consequences.
For me, E10 approval for motorcycles means: I fill up with E10.
That’s not going to get in my tank under any circumstances!
My car gets E10, my mopped premium fuel.
What do lawn mowers and motorcycles have in common? They often do not start in the spring or after a long standstill or only poorly. The reason: the petrol in a tank with air ages quickly. Shelf life is outlined between two months and up to a year.
Empty tanks with a lot of air that are exposed to constant temperature fluctuations are particularly susceptible. Whether it is gasoline with a high or low ethanol content makes no difference in terms of aging. The alcohol only adds another factor to the consequences of the superimposition.
A simple precautionary measure against aging petrol during longer periods of rest is to fill the tank with fresh fuel as much as possible.
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