Fuel Problems in Classic Cars Caused by E10, E5, and Ethanol
Problem after problem—and some we didn’t even know we had.
We enjoy many of the achievements of modern technology. However, some of them also cause headaches. With the introduction of the eco-fuel E10 and the addition of up to 5% bioethanol to “regular” Super Plus gasoline, we’ve created a new, serious problem for ourselves.
E5 and E10 gasoline is no longer permanently stable when exposed to oxygen and begins to degrade after just a few months. The stabilizing additives lose their effectiveness. Many manufacturers guarantee a shelf life of only about 60 days.
After that, the fuel begins to separate, which is often recognizable by a pungent odor. This means that classic car enthusiasts must take effective corrosion-prevention measures themselves. But how can this be achieved when ethanol is present almost everywhere?
Ethanol damages the fuel tank, carburetor, fuel pump, and gaskets
In higher concentrations, the fuel additive ethanol is a very effective solvent. Among other things, it attacks seals, fuel lines, and metals used in the fuel system, such as iron, zinc, and magnesium. This can lead to leaks. Additionally, ethanol causes severe corrosion.
Furthermore, modern vehicles have a closed fuel system, whereas classic cars are constantly exposed to air. In these open systems, additional corrosion occurs because ethanol is hygroscopic and absorbs moisture from the air. At the same time, as the fuel ages, aggressive acetic and formic acids can form, further exacerbating the problem.
The risk of corrosion therefore increases significantly, especially during longer periods of inactivity or less frequent refueling—for example, due to low annual mileage.
Why today’s fuel is problematic for classic cars
Before vehicles were equipped with catalytic converters, the addition of certain phosphates to gasoline helped counteract corrosion. However, since these could damage the catalytic converter, they were replaced by other additives. As the automotive industry continued to evolve, these additives increasingly disappeared from the fuel.
The unleaded gasoline of the 1990s offered significantly better corrosion protection than today’s fuels. This is particularly problematic for the fuel tank, carburetor, and fuel pump.
Gasoline today has a very short shelf life
Therefore, whenever possible, fill up with gasoline that contains no bioethanol or as little ethanol as possible. According to our information as of February 2026, Aral Ultimate 102 contains ether instead of ethanol, according to the manufacturer. Shell V-Power contains no more than 0.7% ethanol.
For extended periods of inactivity, we recommend adding a fuel stabilizer, which is particularly suitable for infrequent drivers and during the winter break. According to the manufacturer, this additive eliminates the need to drain the fuel system. We can confirm this from our own experience, but we cannot guarantee it.
Add the additive to a full tank and then let the vehicle run for about ten minutes. That is all that is required. So far, we have only had positive results.
Gasoline Stabilizer and Fuel Additives for Classic Cars
We carry these additives from Liqui Moly under part numbers 20087 and 10617. The ELF/Total octane booster, part number 21174, has also proven very effective in practice.
Even though many “experts” claim that E10 or E5 gasoline is harmless to vehicles, we see it differently. We only agree with the frequently expressed recommendation to fill the tank to the brim when the vehicle is not in use if you use premium gasoline with no or very little ethanol content.
Another tip has also proven effective for the winter break: Mix about 1% synthetic two-stroke oil into the fuel in the tank.
Diesel Fuel, Bacterial Growth, and HVO as an Alternative
If you own a diesel vehicle, problems can arise here as well. In modern diesel fuels, bacteria can form in open fuel systems, which break down the fuel. This mixture can corrode fuel injectors and fuel pumps. This often results in the need for very expensive repairs.
This is also a major problem in recreational boating, as Peugeot or Perkins diesel engines are frequently installed in these vessels.
However, there is an alternative: use HVO fuel. Bacteria cannot form in it. After refueling, you should warm up the engine so that the HVO diesel reaches the entire fuel system. After turning off the engine, you can top off the fuel line using a canister of HVO.
Practical tips for rarely used vehicles and power tools
And here’s another quick practical tip: We also use high-quality premium gasoline and the gasoline additive for rarely used power tools such as lawn mowers, chainsaws, or similar equipment. These will also start up again without any problems after the winter break.
Fuel classic cars properly and drive them regularly
Always buy the best possible fuel—and drive your vehicle regularly.
This is because all classic cars, regardless of the manufacturer, have a fuel system that is open to the atmosphere. This allows oxygen to reach the fuel—and that is exactly where the problem begins.