January 21, 2020

Improving Detection: Diesel Fuel Dilution of Engine Oils

Diesel fuel dilution of engine oils is a common and serious problem for heavy equipment fleet operators. This issue can lead to a reduction in fuel economy, but can also lead to rough operation, or even catastrophic engine damage. Diesel fuel is one of the highest operating costs for an engine, so maintaining peak fuel economy can add up to significant savings. Unfortunately, there are several mechanical issues which can lower fuel performance during operation.

  • Restricted air intake (plugged air filters)
  • Improper air/fuel ratio (running too rich or too lean)
  • Improper compression or timing
  • Improper engine temperature (running too hot or too cold)
  • Excessive idling / lugging
  • Poor fuel quality / fuel cleanliness

When an engine burns diesel fuel less efficiently, the unburned fuel ‘washes’ down into the crankcase, causing the engine oil to be diluted. Diesel fuel acts as a solvent inside the engine, preventing oil from adhering to metal surfaces, leading to increased temperatures and excessive wear. Also, diesel fuel thins out the engine oil, making the oil less effective at lubrication, carrying a load, or removing heat.

How do fleets typically monitor diesel fuel dilution?

Typically, most fleet operators monitor their fuel consumption closely, and submit oil samples to a commercial oil analysis laboratory. Fuel dilution is generally monitored by evaluating the oil’s viscosity, followed up by a secondary test such as gas chromatography or flash point for confirmation. While laboratory test results are generally valid, they are usually only collected during an oil change, which may only occur every 500 hours. Depending on the severity of the fuel leak, this may be too late, as significant damage to the engine may already have occurred. 

Monitoring diesel fuel dilution in real-time

Fluid Property Sensor

In real-time, a Fluid Property Sensor is used to measure viscosity (along with density, dielectric constant and temperature) of fluids. Besides allowing for a faster notification and response to this issue, being able to trend viscosity over time allows reliability professionals to know whether the issue was caused by a gradual accumulation of diesel fuel (i.e. excessive idling), or a one-time event (i.e. fouled injector tip triggered by overloading conditions, etc.). Sensor data can then be compared with lab tests to confirm results and determine possible causes or if other factors are at play.

Fluid Life now offers a variety of inline oil condition monitors to help fleets monitor their critical assets more closely. Data from these sensors is uploaded to our myLab web platform, and integrated with traditional laboratory results. Our proprietary system automatically integrates and analyzes this data to give you a unified health report of your critical assets, and sends alerts when key parameters change significantly.

Monitoring oil condition properties in real-time typically carries a higher cost than a simple laboratory-based program. As such, it is important to evaluate whether any particular application warrants the added costs.

Fluid Property Sensor

Fluid Life offers a Fluid Property Sensor which uses patented tuning fork technology to monitor the direct and dynamic relationship between multiple physical properties to determine the quality, condition and contaminant loading of fluids such as engine oil, fuel, transmission and brake fluid, hydraulic and gear oils, refrigerants and solvents. Rugged construction with corrosion and contaminant resistant coating for wetted parts allows for installation in high pressure and high flow environments.

Sensor applications:

  • Surface Mining (haul truck engines, large dozer engines, etc.)
  • Marine (main propulsion engines)
  • Rail (locomotive engines)
  • Power Generation (diesel generators)
  • Drilling (diesel generators)

For more information, please contact Fluid Life.


Mark Shierman is the Corporate Director Of Client Services at Fluid Life with over 25 years of experience in oil analysis, lubricants testing, reliability and predictive maintenance. Mark has a BSc in Chemistry and industry certifications including CRL, CLS, and OMA. Mark and his team of experts look forward to assisting you and answer any questions you may have.