Cold Start Challenges in the Wacker Neuson RTSC3 with Kubota Engine

[MikePhua]

The RTSC3 and Its Role in Soil Compaction
The Wacker Neuson RTSC3 is a remote-controlled trench roller designed for compacting cohesive soils in confined spaces. With dual vibratory drums and infrared remote operation, it’s a staple in utility trenching, pipeline bedding, and foundation prep. The RTSC3 is offered with either a Kohler/Lombardini or Kubota diesel engine, both air-cooled and engineered for rugged environments. While the Kohler variant is known for its longer glow plug cycle, the Kubota-powered version—often preferred for its reliability and parts availability—has shown quirks in cold-start behavior.
Glow Plug Timing and Cold Weather Performance
The Kubota engine in the RTSC3 initiates a glow plug cycle of approximately 5 seconds, which is significantly shorter than the 30-second cycle found in the Kohler-powered units. This brief heating period is often insufficient in ambient temperatures below 45°F (7°C), leading to extended cranking and misfires. Operators report needing to repeat the glow cycle six to eight times to achieve a rough ignition pattern in colder conditions.
Glow plugs are resistive heating elements that pre-warm the combustion chamber to aid fuel ignition. In diesel engines, especially indirect injection types like those used in compact rollers, adequate preheating is critical. A 5-second cycle may not allow the plugs to reach the necessary temperature, especially when ambient air and cylinder walls are cold.
Manual Override and Electrical Considerations
Some technicians have explored manually wiring a push-button circuit to extend glow plug activation. While theoretically effective, this approach risks back-feeding the ECU (Electronic Control Unit) unless the factory feed wire is isolated. The RTSC3’s control logic requires feedback from all systems before allowing engine turnover, so any modification must preserve signal integrity to avoid triggering faults or lockouts.
Before attempting a manual override, it’s essential to:

• Confirm full voltage delivery to the glow plug rail during the factory cycle
  
• Inspect the glow plug relay for voltage drop or contact failure
  
• Measure glow plug resistance (target: ~0.9 ohms per plug)
  
• Ensure battery voltage remains stable during preheat and cranking
  

In one case, a technician discovered that although voltage was present at the plug harness, the plugs themselves were only reaching lukewarm temperatures—insufficient for reliable combustion. This was traced to a weak relay that failed under load despite passing static tests.
Valve Lash and Combustion Efficiency
Valve lash—the clearance between the rocker arm and valve stem—affects valve timing and seating. While Kubota recommends checking lash at 800 hours, early inspection can reveal tight or loose valves that compromise compression. In cold starts, proper valve seating ensures that combustion pressure builds quickly, reducing misfire risk.
Symptoms of poor valve lash include:

• Hard starting despite warm glow plugs
  
• Rough idle immediately after ignition
  
• White smoke during cranking
  
• Delayed throttle response
  

Adjusting valve lash requires removing the valve cover and using feeler gauges to set intake and exhaust clearances per manufacturer spec. Though the RTSC3 in question had only 390 hours, early lash inspection was deemed worthwhile given the cold-start struggle.
Comparative Engine Behavior Across Fleets
Operators with experience across multiple machines note that other Kubota engines—such as those in Bobcat A300 loaders—run longer glow cycles and start reliably in sub-freezing conditions. Similarly, Deutz diesels in Bobcat 442 excavators initiate proportional glow cycles based on ambient temperature, often reaching 10 seconds or more. Even older Cummins 8.3L engines in L-series trucks run 30-second cycles in cold weather.
This discrepancy raises questions about why the RTSC3’s Kubota ECU limits glow time to just 5 seconds. It may be a design compromise to protect battery life or reduce emissions, but in practice, it hampers usability in colder climates.
Field Experience and Practical Workarounds
In Montana, one operator found that cycling the glow plugs repeatedly—despite the cooling interval between cycles—was the only way to coax the engine into firing. Once started, the machine ran flawlessly, even after sitting idle for hours. This suggests that the engine itself is mechanically sound, and the issue lies purely in pre-combustion preparation.
Another technician proposed isolating the glow plug circuit and installing a timed relay or manual switch, allowing extended heating without interfering with the ECU. While promising, this solution requires careful wiring and may void warranty or trigger fault codes if not executed properly.
Recommendations for Reliable Cold Starts
To improve cold-start reliability in the RTSC3:

• Test glow plugs individually for heat output and resistance
  
• Verify full voltage delivery during the glow cycle
  
• Inspect and replace the glow plug relay if voltage drop is detected
  
• Consider valve lash inspection if hours exceed 300
  
• Explore safe manual override options with ECU isolation
  
• Use fuel additives to improve combustion in cold weather
  
• Store the machine in a warmer environment or preheat the engine externally
  

Conclusion
The Wacker Neuson RTSC3 with Kubota power is a dependable compactor once running, but its short glow plug cycle presents challenges in colder climates. While the engine is fundamentally robust, overcoming the limitations of its preheat logic may require creative electrical solutions and proactive maintenance. In the world of diesel compaction equipment, cold starts are a test of both engineering and operator ingenuity—and the RTSC3 is no exception.