Fuel Phase Separation

Modern fuels are engineered to perform reliably under a wide range of conditions, but they aren’t immune to degradation. One of the most common and costly problems affecting fuel quality today is phase separation—a chemical and physical process that can lead to engine damage, pump failures, and expensive remediation for fuel stations.

What Is Phase Separation?

Phase separation occurs when the components of a fuel blend—most commonly ethanol-blended gasoline—break apart into distinct layers. Ethanol is highly hygroscopic, meaning it absorbs water from the air. When enough water accumulates in the fuel, the ethanol-water mixture becomes too heavy to stay suspended and settles at the bottom of the storage tank.

This results in two layers:

1. A lower layer of ethanol-water solution

2. An upper layer of low-octane gasoline

Both layers are harmful: the lower layer can cause corrosion and engine damage, and the upper layer provides poor combustion performance.

How Fuel Degradation Affects Fuel Stations

Fuel stations depend on maintaining clean, dry, and stable fuel in their underground tanks. When degradation or phase separation occurs:

• Dispensers pump contaminated fuel — Because the tank’s pickup point is near the bottom, the ethanol-water layer can become the first thing pumped into vehicles. Most fuel stations opt to have monitoring systems that alert to rising water levels in the bottom of the tank and prevent motorists from pumping from the bottom layer.

• Corrosion of tank systems — Water and ethanol accelerate corrosion of steel tanks, fittings, and dispensing equipment. This can cause leaks or broken components in the bottom of the tank, resulting in the leaking of fuel into the water table and water streams into the fuel tank.

• Clogged filters and pump failures — Fuel filters become overwhelmed by particulates, sludge, or corrosion, leading to frequent maintenance and downtime.

• Regulatory and financial consequences — Stations may face environmental compliance issues, tank cleaning expenses, lost fuel inventory, and customer claims.

Fuel degradation isn’t just inconvenient—it can become a major operational and financial burden.

How Degraded Fuel Harms Motor Vehicles

When phase-separated or oxidized fuel enters a vehicle:

• Engine misfires, hesitation, or stalling occur due to poor combustion.

• Fuel pump and injector damage may result from water contamination or debris.

• Corrosion in fuel system components such as rails, injectors, and tanks can develop.

• Check engine lights often activate because of incorrect air-fuel ratios.

In severe cases, vehicles can become dangerous to drive and require costly repairs.

Management & Treatment Options for Fuel Stations

Fuel station operators can reduce the risk and impact of phase separation with a combination of prevention and remediation:

1. Water Management

• Routinely test for water using paste, tank monitors, or manual sampling.

• Ensure tank lids, caps, and gaskets are sealed to prevent rain and groundwater intrusion.

• Address ventilation issues that allow excess condensation.

2. Regular Tank Maintenance

• Schedule periodic inspections, pump outs, and fuel-polishing services.

• Remove sludge and microbial growth that contribute to degradation.

3. Additives & Fuel Conditioning

• Use approved additives to stabilize fuel, disperse water, or slow oxidation.

• Note that additives cannot reverse severe phase separation—only prevent or mitigate it.

4. Professional Remediation

If phase separation has already occurred:

• Pump out and properly dispose of the separated layer.

• Clean the tank and lines.

• Refill with fresh fuel and test before reopening dispensers.

Early action minimizes damage and liability.

What Motor Vehicle Owners Should Do if They Suspect Bad Fuel

If you think you’ve filled up with degraded fuel, act quickly:

1. Stop driving if possible.
   Continued operation can draw contaminated fuel deeper into the system.

2. Document everything.
   Keep your receipt, note the time and location, and take pictures if problems occur.

3. Contact the fuel station.
   Reputable stations often investigate and may cover repair costs if the issue is confirmed.

4. Have a mechanic diagnose the vehicle.
   A professional can test fuel samples, check for water, and inspect for injector or pump damage.

5. Drain and replace the fuel if necessary.
   Vehicles contaminated with water-ethanol layers often require tank draining, filter replacement, and sometimes injector cleaning.

Addressing the issue early reduces the chance of severe engine damage.

Fuel phase separation is a largely preventable problem—but once it happens, its effects can be far-reaching. By understanding how degradation occurs and taking proactive steps, fuel station operators can protect their systems and customers. Likewise, drivers who act quickly after encountering bad fuel can minimize repair costs and avoid prolonged downtime.

Cain Services is proud to partner with fuel station operators to provide maintenance of fuel tanks and lines by removing accumulated water from sumps, tanks, and pumps before they become a problem to motorists. We also routinely provide support once phase separation has been confirmed. In areas with higher precipitation and a high water table, these problems are more common and require more frequent inspections and maintenance. We placed our operations in the heart of East Tennessee so that we can serve the needs of fuel stations in an area that is known for both its high water table and frequent precipitation.