Diagnosing Driveability Issues in the Gehl 55DH Telehandler

[MikePhua]

The Gehl Legacy in Material Handling
Gehl Company, founded in 1859 in Wisconsin, began as a manufacturer of agricultural implements and evolved into a major player in compact construction equipment. By the early 2000s, Gehl had established itself in the telehandler market with models like the DL10H-55 and 55DH, designed for high-reach lifting, rugged terrain, and versatile job site applications. These machines were widely adopted across North America and Europe, particularly in construction, warehousing, and industrial maintenance.
The 55DH telehandler features a four-section boom with a top-hat design, a turbocharged 115 hp engine, and a lift capacity of 5,000 pounds. With outriggers deployed, it can achieve a forward reach of over 40 feet, making it ideal for tasks requiring extended reach and stability. Its drivability, however, depends heavily on the health of its engine management system, cooling circuit, and safety interlocks.
Symptoms of Driveability Problems
Operators encountering driveability issues in the 55DH often report:

• Engine starts reliably but shuts down after 15–30 minutes
  
• Restart is only possible after a cooldown period
  
• Radiator top hose becomes extremely hot while the bottom remains cold
  
• Fuel pressure appears normal, but engine cuts fuel unexpectedly
  
• No active fault codes visible without OEM-specific diagnostic software
  

These symptoms suggest a thermal or sensor-related shutdown, often triggered by the machine’s ECU interpreting abnormal readings from coolant temperature, oil pressure, or fluid levels.
Terminology Notes

• ECU (Electronic Control Unit): The onboard computer that monitors engine parameters and controls shutdown logic.
  
• Coolant Sensor: A thermistor that measures engine coolant temperature and signals the ECU.
  
• Thermostat Housing: The enclosure that regulates coolant flow based on temperature.
  
• Outriggers: Stabilizing legs that extend from the chassis to improve lifting stability.
  

Root Causes and Diagnostic Pathways
The most common cause of shutdown in the 55DH is overheating or a false overheat signal. If the top radiator hose is hot and the bottom cold, coolant circulation is likely restricted. This can be due to:

• A stuck thermostat preventing coolant flow
  
• Airlock in the cooling system
  
• Faulty coolant temperature sensor sending incorrect data
  
• Clogged radiator or internal corrosion
  
• Weak water pump impeller
  

To diagnose:

• Remove the thermostat and test it in hot water to verify opening temperature
  
• Replace the coolant sensor with an OEM-spec unit
  
• Bleed the cooling system to eliminate trapped air
  
• Use an infrared thermometer to compare inlet and outlet temperatures
  
• Inspect the radiator core for debris or scale buildup
  

A contractor in Arizona reported similar symptoms during summer operations. After replacing the thermostat and sensor, the machine ran continuously without shutdown, confirming the issue was sensor-related rather than mechanical overheating.
Electrical Interlocks and Fuel Cutoff Behavior
The 55DH’s ECU monitors several safety parameters. If coolant temperature exceeds threshold, or if oil pressure drops below spec, the ECU will cut fuel to the injection pump. Even if fuel pressure at the filter head is adequate, the pump may be electronically disabled.
To verify:

• Install a pressure gauge inline with the fuel filter
  
• Check voltage at the fuel shutoff solenoid during operation
  
• Scan for stored fault codes using compatible diagnostic tools
  
• Inspect wiring harnesses for abrasion or loose connectors
  

In one case, a telehandler in Ontario would shut down mid-lift. The issue was traced to a corroded ground wire near the ECU, causing intermittent signal loss. Cleaning and resealing the connection resolved the problem.
Recommendations for Reliable Operation
To improve drivability and prevent shutdowns:

• Replace thermostat and coolant sensor every 2,000 hours or sooner if symptoms appear
  
• Flush and refill coolant annually with manufacturer-approved fluid
  
• Clean radiator fins monthly and inspect for leaks
  
• Secure all wiring harnesses and apply dielectric grease to connectors
  
• Maintain a diagnostic log of shutdown events and ambient conditions
  

Fleet managers should also consider installing a manual override switch for the fuel solenoid in emergency scenarios, though this must comply with safety regulations and be used cautiously.
Operator Anecdotes and Field Wisdom
A rental yard in Texas retrofitted its 55DH fleet with external coolant temperature gauges to monitor real-time readings. This helped operators identify overheating before shutdown occurred. In British Columbia, a crew added a secondary electric fan to improve airflow during summer lifts, reducing thermal load and extending uptime.
One operator in Georgia recalled how his telehandler would shut down during roofing work. After replacing the coolant sensor and bleeding the system, the machine ran flawlessly for the rest of the season.
Conclusion
Driveability issues in the Gehl 55DH often stem from thermal miscommunication between sensors and the ECU. While the machine’s design is robust, its reliance on accurate sensor data means that even minor faults can trigger shutdowns. By understanding the interplay between cooling, electrical, and fuel systems—and applying methodical diagnostics—operators can restore reliability and keep the 55DH performing at its full potential.