Identifying Vintage Donaldson Oil Bath Air Cleaners and Their Automotive Origins

[MikePhua]

The Donaldson Legacy in Engine Filtration
Donaldson Company, founded in 1915, has been a global leader in filtration systems for over a century. Their oil bath air cleaners were once standard equipment on agricultural tractors, military vehicles, and early commercial trucks. Before the widespread adoption of dry paper filters, oil bath systems offered a reliable method for trapping airborne dust and debris in harsh environments. These units used a reservoir of oil to capture contaminants as air passed through a mesh or vane system, making them ideal for off-road and industrial applications.
By the 1960s, oil bath filters began to fade from mainstream use, replaced by more compact and maintenance-free dry filters. However, many vintage machines still rely on these systems, and collectors often seek original units for restoration projects.
Unusual Dimensions and Clues to Application
A particularly large Donaldson oil bath unit measuring approximately 28.5 inches in diameter and 16 inches in height—with two outlet ports sized at 3 inches and 7/8 inch—raises questions about its original application. The absence of a visible inlet and the presence of dual outlets suggest a specialized configuration, possibly for a multi-function engine setup.
Such dimensions exceed those found on typical Willys Jeep or Jeepster models, which used smaller, more compact air cleaners. The mounting bracket and overall form factor hint at a heavy-duty automotive or industrial origin, possibly from a GM-powered truck, military transport, or stationary engine.
Dual Outlet Function and Engine Integration
The presence of two outlet ports is uncommon in standard oil bath designs. The larger outlet likely served as the primary air path to the intake manifold, while the smaller outlet may have been used for vapor scavenging or auxiliary air routing. In some configurations, the smaller outlet connects to the valve cover or crankcase to draw blow-by gases back into the intake stream—a rudimentary form of emissions control.
Alternatively, the smaller outlet could have fed an onboard air compressor, a feature found in military vehicles and fire apparatus. These systems required clean air for pneumatic tools or brake systems, and routing through the oil bath ensured filtration consistency.
Restoration and Collector Interest
Vintage air cleaners like this Donaldson unit are highly sought after by restorers of classic trucks, tractors, and military vehicles. However, identifying the exact model and application can be challenging due to limited documentation and discontinued part numbers. Donaldson’s corporate archives may not include legacy units, and modern support channels often lack interest in obsolete components.
Collectors and restorers often rely on visual matching, bracket design, and outlet configuration to trace origins. Online communities dedicated to “Just Old Trucks” or military surplus restoration can be valuable resources for identification and sourcing.
Preservation Tips and Reuse Potential
If the unit is in NOS (new old stock) condition, it holds significant value for restoration. To preserve and potentially repurpose it:

• Clean the interior with kerosene or light solvent to remove any residue
  
• Inspect the mesh or vane system for corrosion or blockage
  
• Repaint the exterior with heat-resistant enamel to match original finish
  
• Replace any gaskets or seals with oil-resistant rubber
  
• Mount temporarily on a test engine to verify airflow and fitment
  

Even if the original application remains unknown, the unit can be adapted for custom builds, stationary engines, or display purposes in a vintage shop or museum.
Conclusion
Large-format Donaldson oil bath air cleaners with dual outlets represent a unique chapter in engine filtration history. While their exact origins may be elusive, their design hints at heavy-duty automotive or industrial use, possibly tied to GM-powered platforms or military-grade equipment. For collectors and restorers, these units offer both functional value and historical intrigue—reminders of a time when filtration was mechanical, maintenance was hands-on, and every part told a story.