Using Waste Oil as Diesel Substitute in Older Equipment

[MikePhua]

The Rise of Alternative Fuels in Heavy Machinery
As fuel prices fluctuate and environmental regulations tighten, operators of older diesel-powered equipment have increasingly explored alternative fuel sources. One such method involves blending waste oil—typically used engine oil or automatic transmission fluid (ATF)—with diesel fuel. This practice, while controversial, has gained traction among small-scale operators, especially in rural areas where access to clean diesel may be limited and waste oil is abundant.
The concept is simple: filter the waste oil to remove contaminants, blend it with diesel at a controlled ratio, and burn it in older diesel engines. While modern Tier III and Tier IV engines are highly sensitive to fuel purity due to high-pressure injection systems and emissions controls, legacy machines with mechanical injection systems often tolerate such mixtures surprisingly well.
Terminology Annotation
- Waste Oil: Used lubricating oil collected from engines, transmissions, or hydraulic systems, often containing carbon, metal particles, and additives.
- ATF (Automatic Transmission Fluid): A petroleum-based fluid used in vehicle transmissions, known for its detergent properties and low viscosity.
- Centrifuge: A device that spins fluids at high speed to separate contaminants from usable oil based on density.
- HUEI (Hydraulic Electronic Unit Injector): A high-pressure fuel injection system used in modern diesel engines, sensitive to fuel quality and viscosity.
Field Experiences and Anecdotal Evidence
Operators of older Caterpillar dozers, Massey Ferguson tractors, and Detroit Diesel-powered sawmills have reported successful use of waste oil blends. In one case, a D8H dozer ran for years on a 50/50 mix of diesel and filtered waste oil without noticeable performance loss. The filtration system used was homemade, involving layers of cloth and foam to remove particulates. Water was allowed to settle out naturally in holding tanks before blending.
Another operator in Virginia attempted to use commercially “cleaned” waste oil in his fleet of trucks. Despite investing over $3,000 in a filtration system, drivers reported reduced pulling power and had to downshift on inclines. The injection pump technician warned that even trace contaminants could affect pump timing and injector spray patterns, leading to poor combustion and increased wear.
Risks and Limitations of Waste Oil Fueling
While older engines may tolerate waste oil blends, several risks must be considered:

• Injector pump damage from carbon particles or varnish buildup
  
• Incomplete combustion leading to increased soot and exhaust odor
  
• Cold weather performance issues due to higher viscosity
  
• Legal restrictions on burning waste oil without permits
  
• Road tax violations if used in on-road vehicles without proper documentation
  

In Canada, for example, burning waste oil is prohibited without specific licensing. In the United States, using untaxed fuel blends on public roads can result in fines exceeding $2,000, as one operator discovered after a roadside inspection.
Recommendations for Safe Use
To minimize risk and improve performance:

• Use only in pre-1995 diesel engines with mechanical injection systems
  
• Filter waste oil using multi-stage systems including centrifuge and sedimentation
  
• Blend at conservative ratios (e.g., 10–20% waste oil to diesel)
  
• Monitor exhaust color and engine temperature during operation
  
• Replace fuel filters more frequently and keep spares on hand
  
• Avoid use in Tier III or Tier IV engines with electronic injectors and emissions controls
  

Some operators report success using ATF as a blend component due to its detergent content and lower viscosity. However, even ATF must be filtered and tested for water content before use.
Manufacturer Perspectives and Controlled Systems
Caterpillar has experimented with controlled waste oil injection in large haul trucks using an Oil Renewal System (ORS). This system meters filtered engine oil into the fuel supply under ECM control, allowing extended oil change intervals and reduced waste disposal. The system is calibrated to engine load and fuel consumption, ensuring safe combustion without compromising engine life.
While this approach is not available on smaller machines, it demonstrates that with proper engineering and monitoring, waste oil can be repurposed effectively. However, it requires precise filtration, metering, and trend analysis—far beyond the capabilities of most field setups.
Conclusion
Using waste oil as a diesel substitute in older equipment is feasible under specific conditions, but it demands careful filtration, conservative blending, and awareness of legal and mechanical risks. For legacy machines operating off-road, this practice can reduce fuel costs and repurpose waste streams. However, it is not suitable for modern engines or road-going vehicles without regulatory compliance. As fuel systems evolve, the margin for error narrows—making informed experimentation and mechanical literacy essential for those pursuing alternative fuels.