A generator is only as reliable as the fuel it depends on.

In Texas—where heat, humidity, and long-term fuel storage conditions vary widely—diesel degradation is one of the leading contributors to generator performance problems. While many facility teams invest heavily in mechanical preventive maintenance, load bank testing, and electrical inspections, the fuel tank is often overlooked.

This is a critical error. Fuel contamination happens slowly and quietly. It doesn't trigger a "Check Engine" light until the moment the generator tries to pull a heavy load.

This expanded guide explains why modern diesel fuel deteriorates faster than ever, how "Texas factors" accelerate the process, and what facility teams must do to maintain a reliable fuel supply.

Why Diesel Fuel Deteriorates in Texas

Many Facility Managers remember the days when you could store diesel fuel for 5–10 years without issue. Those days are gone.

Today's Ultra-Low Sulfur Diesel (ULSD) is cleaner burning, but it is also less stable. The refining process that removes sulfur also removes natural stabilizers, giving modern diesel a shelf life of only 6 to 12 months if left untreated.

Here are the leading contributors to fuel death in Texas:

1. Heat Accelerates Oxidation

Diesel fuel is organic. Like food, it spoils faster in the heat. High ambient temperatures cause diesel molecules to break down and oxidize. This chemical reaction forms gums, varnishes, and sticky deposits that darken the fuel.

• The Science: In chemistry, the rate of reaction typically doubles for every 10°C (18°F) rise in temperature. A tank baking in the 105°F Texas sun degrades significantly faster than one in a cool basement.

2. Condensation Introduces Water

As Texas temperatures fluctuate between scorching days and cooler nights, the air inside the fuel tank expands and contracts. This "breathing" pulls moist air into the tank, where it condenses on the walls and drips into the fuel. Water is heavier than diesel, so it sinks to the bottom. Since the fuel pickup line is usually raised a few inches off the bottom, this water can sit undetected for years—until it rises high enough to be sucked into the engine.

3. Microbial Growth ("Diesel Bugs")

There is a common myth that "algae" grows in diesel tanks. Since there is no sunlight inside a tank, it isn't algae—it is bacteria and fungi. These microbes live in the water layer at the bottom of the tank and feed on the hydrocarbons in the fuel. As they multiply, they produce a dark, slimy waste product (biomass) and acidic byproducts that corrode metal tank bottoms.

Related Reading: Fuel issues often trigger other mechanical failures. Read: [Link to Blog 1: Why Generators Fail: Top 7 Early Warning Signs]

4. Sediment and Asphaltenes

As fuel oxidizes, heavy particles called asphaltenes drop out of the solution. These hard, black particles settle on the tank floor. During a weekly "no-load" test, the fuel flows gently, and the sediment stays put. But during a real outage, when the generator runs at full capacity, the high-volume fuel return flow stirs up this sediment, sucking it straight into the filters.

How Fuel Contamination Affects Generator Reliability

Fuel quality issues often stay hidden until the generator is required to support building load. Here is how contamination impacts performance:

1. The "Start-Then-Die" Scenario

This is the most frustrating failure mode. The generator starts initially (using the clean fuel in the lines), but as soon as it begins drawing from the tank, the fuel filters clog with slime or sediment. Result: The engine starves for fuel and shuts down within minutes—usually right when the facility needs power the most.

2. Injector Fouling and Damage

Modern Tier 4 Final generators use High-Pressure Common Rail (HPCR) fuel systems. These injectors operate at extreme pressures (30,000+ PSI) and have tolerances measured in microns. Even microscopic gums or varnish can cause these injectors to stick or spray poorly. Symptoms:

• Incomplete combustion.

• Black smoke / Wet Stacking.

• Loss of rated power output.

3. Irregular Engine Performance

Poor fuel quality lowers the cetane rating (combustibility) of the diesel. This leads to rough idling, surging RPMs, and an inability to accept sudden load steps (like an elevator starting or a chiller kicking on).

Related Reading: Irregular combustion often leads to Wet Stacking. Learn more in: [Link to Blog 3: How Often Should Industrial Generators Be Load Bank Tested?]

4. ATS Transfer Failures

This sounds unrelated, but it isn't. If the generator is surging or running at an unstable frequency (e.g., 58Hz instead of 60Hz) due to bad fuel, the Automatic Transfer Switch (ATS) may reject the generator source to protect the building loads.

Related Reading: See how the ATS interprets generator power quality in: [Link to Blog 4: ATS Failure Points and How to Identify Them]

How to Maintain Fuel Quality in Standby Generators

Fuel quality issues are almost always preventable when maintenance programs include proper fuel management.

1. Routine Fuel Sampling and Lab Testing

You cannot judge fuel just by looking at the top of the tank. A technician must use a "bacon bomb" or similar tool to pull a sample from the bottom of the tank. TIIS recommends annual lab testing to check for:

• Water and sediment content (BS&W).

• Cetane index.

• Microbial growth (bacteria/fungi culture).

• Cloud point (for winter readiness).

2. Fuel Polishing (Filtration and Circulation)

Fuel Polishing is the process of mechanically cleaning the fuel. A mobile rig connects to the tank and circulates the diesel through a series of high-capacity filters and water separators.

• It removes: Free water, emulsified water, sludge, and particulate matter down to 1-5 microns.

• It restores: The fuel is returned to the tank clean and dry.

Who needs polishing? Facilities with large tanks that don't burn through their fuel supply every 12 months (e.g., data centers, hospitals, office buildings) should polish their fuel on a schedule.

3. Chemical Treatment

Polishing removes the result of the problem, but chemicals help treat the source.

• Biocides: Kill the microbial growth.

• Stabilizers: Slow down the oxidation process.

• Corrosion Inhibitors: Protect the tank walls.

Related Reading: Proactive maintenance reduces overall downtime risks. Read: [Link to Blog 6: What a Generator Downtime Risk Assessment Includes]

4. Keep the Tank Full (But Not Too Full)

Keeping a tank full reduces the volume of air space ("ullage"), which minimizes the surface area available for condensation to form. However, always leave room for thermal expansion—diesel expands as it gets hot!

Why Fuel Problems Often Go Undetected

• Visual Deception: Diesel can look bright and clear at the inspection port while a 2-inch layer of sludge sits at the bottom.

• Lack of Testing: Standard Generator PMs usually include changing the filters, but they rarely include sampling the bulk fuel in the tank.

• Low-Load Usage: As mentioned, engines run fine on marginally bad fuel at idle. They only fail when pushed to 100% load.

Related Reading: Batteries are the only thing that fail more often than fuel. Read: [Link to Blog 7: Why Battery Failure Is the #1 Reason Generators Don’t Start]