Vietnam has been transitioning to environmentally friendly fuels for years. Since 2018, RON 92 gasoline has been replaced by E5 RON 92, and now E10 gasoline is more widely available. Many countries are adopting this fuel to reduce emissions and consumer costs. However, this shift requires users to be mindful of fuel storage practices.

An E10 gasoline pump at a gas station in Ho Chi Minh City. Photo: Ho Tan

An E10 gasoline pump at a gas station in Ho Chi Minh City. Photo: Ho Tan

E10 gasoline is a blend of 90% petroleum gasoline and 10% bioethanol. Compared to petroleum gasoline, E10 is typically cheaper, more environmentally friendly due to reduced emissions, and has a slightly higher octane rating, benefiting engines requiring anti-knock properties.

However, ethanol's hygroscopic nature makes E10 prone to separation or sediment formation when stored for extended periods, especially in infrequently used vehicles. This can lead to difficulty starting, reduced engine performance, or fuel injection system blockages.

Preventing fuel stagnation

According to BP, petroleum gasoline stored in sealed containers in dry places like gas station tanks can maintain its quality for up to a year. However, once exposed to the outside environment, it remains stable for only about 6 months at 20 degrees Celsius and 3 months at 30 degrees Celsius.

Ethanol gasoline has a shorter lifespan than petroleum gasoline under the same conditions. In a non-airtight tank, like that of an infrequently used vehicle, its optimal lifespan is only about a month. BP recommends adding about 1/3 of a tank of fresh gasoline before starting the engine after a long period of inactivity. This helps "refresh" the old fuel. With ethanol blends, the fresh gasoline also removes accumulated moisture and dries the system.

Risk of phase separation from water contamination

A specific risk with ethanol gasoline is "phase separation." This occurs when water enters the fuel tank, causing the ethanol to separate from the gasoline. The extent of separation depends on the ethanol percentage, gasoline composition, ambient temperature, and contamination level.

Phase separation in ethanol gasoline: the upper layer (orange) is gasoline with reduced ethanol concentration, the black sediment below is a mixture of ethanol and water. Photo: BP

Phase separation in ethanol gasoline: the upper layer (orange) is gasoline with reduced ethanol concentration, the black sediment below is a mixture of ethanol and water. Photo: BP

BP recommends ensuring the fuel tank is free of significant water before using ethanol-containing fuel. Leaving the tank exposed to humidity or rain increases the risk of phase separation. If this happens, the only solution is to drain all fuel, remove the water, and refill with fresh fuel to prevent engine problems.

Solutions for infrequently used vehicles

For vehicles left unused for extended periods, such as a month, drivers should fill the tank to limit moisture condensation. Additionally, using a fuel stabilizer can prevent E10 degradation, limit phase separation, and protect the fuel system.

Fuel stabilizers act as preservatives, preventing degradation during storage. They typically contain antioxidants to prevent sediment formation, corrosion inhibitors to protect metal parts from rust, and water absorbers or dispersants to reduce phase separation risk. Adding the solution to the fuel tank and running the engine for a few minutes distributes it throughout the fuel system, keeping the gasoline stable for longer, potentially 12-24 months instead of just a few.

Fuel stabilizer solutions in the US market. Photo: Trueprepper

Fuel stabilizer solutions in the US market. Photo: Trueprepper

When using a fuel stabilizer, it's essential to mix the correct ratio of solution to fuel for optimal effectiveness. Users should check their fuel tank capacity and mix at a typical ratio of 30-60 ml per 10 liters of gasoline.

Fuel stabilizers are not as widely available in Vietnam as engine oil or regular gasoline additives, but they can be found in auto parts stores or online marketplaces.

Ho Tan