Bomag BW80 Loses Drive When Hydraulic Oil Heats Up

[MikePhua]

The Bomag BW80 ADH-2 and Its Role in Light Compaction
The Bomag BW80 ADH-2 is a compact tandem vibratory roller designed for asphalt patching, sidewalk repair, and small-scale compaction tasks. Manufactured by Bomag GmbH, a German company founded in 1957 and now part of the Fayat Group, the BW80 series has been widely adopted across Europe, Asia, and the Americas. Bomag’s reputation for precision engineering and durable hydraulics helped the BW80 become a staple in municipal fleets and small contractor operations.
With an operating weight of approximately 1.5 tons and a working width of 800 mm, the BW80 ADH-2 is powered by a Kubota diesel engine and features hydrostatic drive to both drums. Its compact footprint and maneuverability make it ideal for tight urban environments and semi-rough terrain—at least when the hydraulic system is functioning properly.
Symptoms of Drive Loss on Uneven Terrain
Operators have reported that the BW80 performs normally when cold, moving forward and backward across all terrain types. However, once the hydraulic oil reaches operating temperature, the machine struggles or fails to move on uneven surfaces. This issue is particularly pronounced when climbing slight grades or transitioning over compacted gravel.
Typical symptoms include:

• Normal drive when cold
  
• Loss of traction or complete stall when hot
  
• No fault codes or warning lights
  
• Vibration system continues to function
  

Terminology:

• Hydrostatic Drive: A propulsion system using hydraulic fluid to transmit power from pumps to motors.
  
• Tandem Roller: A compactor with two steel drums, one front and one rear, both capable of vibration.
  

A contractor in Trinidad noted that the issue persisted even after replacing the hydraulic oil and filter, suggesting that fluid degradation was not the root cause.
Root Cause Identified in Travel Pump and Brake Solenoid
Upon further inspection, two key issues were discovered:

1. The hydraulic travel pump had internal wear that reduced sealing efficiency. When the oil was cold and more viscous, the pump could maintain pressure. As the oil thinned with heat, internal leakage increased, leading to pressure loss and drive failure.
   
2. The brake solenoid coil was receiving power and attempting to actuate, but lacked the strength to overcome hydraulic pressure when hot. This meant the brake remained partially engaged, preventing movement.
   

Terminology:

• Solenoid Coil: An electromagnetic component that actuates valves or brakes when energized.
  
• Internal Leakage: Fluid bypass within a pump or motor due to worn surfaces or seals.
  

The travel pump was removed and polished to restore sealing surfaces. The brake solenoid was temporarily replaced with the vibration system’s coil, which had sufficient strength to actuate under pressure.
Why Heat Exacerbates Hydraulic Weakness
Hydraulic oil viscosity decreases as temperature rises. While this improves flow, it also reduces the oil’s ability to maintain pressure in worn components. In systems with marginal sealing, such as aged pumps or motors, this leads to performance degradation.
Factors that amplify heat-related issues:

• Worn pump pistons or valve plates
  
• Contaminated or aerated oil
  
• Undersized cooling systems
  
• Weak solenoids or electrical connections
  

Terminology:

• Viscosity: A fluid’s resistance to flow; lower viscosity means thinner oil.
  
• Valve Plate: A precision-machined surface that directs fluid flow within a pump or motor.
  

In 2022, a fleet in Queensland reported similar issues across three BW80 units. After replacing solenoids and rebuilding pumps, drive reliability improved significantly, especially on warm days and rough terrain.
Preventive Maintenance and Component Upgrades
To avoid drive loss in compact rollers like the BW80, regular hydraulic system inspections are essential. Operators should monitor oil condition, solenoid strength, and pump performance—especially in older machines approaching 2,000+ operating hours.
Recommended maintenance:

• Replace hydraulic oil every 500 hours or annually
  
• Inspect solenoid coils for heat damage and resistance drop
  
• Check pump pressure output at operating temperature
  
• Clean or replace filters every 250 hours
  

Upgrade options:

• Install higher-torque solenoids rated for elevated pressure
  
• Add auxiliary cooling fans to reduce oil temperature
  
• Use synthetic hydraulic oil with stable viscosity across temperature ranges
  

Terminology:

• Operating Hours: Total time a machine has run, used to schedule maintenance.
  
• Synthetic Oil: Engineered lubricant with superior thermal stability and oxidation resistance.
  

A technician in Ontario shared that switching to synthetic hydraulic oil reduced operating temperature by 8°C, improving drive consistency in summer conditions.
Conclusion
The Bomag BW80 ADH-2 is a reliable compactor when its hydraulic system is in good health. However, heat-related drive loss is a known issue in aging units, often caused by internal pump wear and weak brake solenoids. By polishing pump internals, replacing solenoids, and maintaining fluid integrity, operators can restore full functionality and extend machine life. In compact equipment, small hydraulic inefficiencies can have outsized effects—especially when terrain gets rough and the oil gets hot.