Resolving Hydraulic and Cooling Issues on the Gehl 1648 Asphalt Paver

[MikePhua]

Overview of the Gehl 1648 Hydraulic & Cooling Systems
The Gehl 1648 (or 1648 Plus) asphalt paver uses a hydraulic-driven forward drive and material handling system combined with a coolant-regulated diesel engine. Hydraulic pressure powers both the track drive and auger/screed functions, while engine cooling relies on a thermostatic circuit and fan.
Typical Symptoms with the 1648
Reported issues include:

• Overheating during extended operations (water temp approaching 220 °F)
  
• Hydraulic pressure loss or drive motors failing under load
  
• Steering valve leaks or internal leakage
  
• Steer valve control sticking or poor responsiveness
  

These symptoms suggest problems in cooling flow, hydraulic seals, or drive circuit integrity.
Common Root Causes
These recurring fault areas often affect reliability:

• Cooling system limitations
  • Radiator cores blocked with debris
    
  • Failed thermostats or fan clutch malfunctions
    
    
• Hydraulic system wear or contamination
  • Worn seals in steering or drive valves
    
  • Dirty filters or varnish build-up
    
  • Drive motor or pump component failure indicated by glitter‑like wear particles in filters
    
    
• Seal degradation in steer valve sections
  • O-ring or seal failure causing internal leaks
    
  • Incorrect installation without proper lubrication
    
    

Diagnostic & Repair Strategies
Follow this structured approach for effective troubleshooting:

• Start the machine and monitor coolant temperature. If reaching ~220 °F, check radiator airflow, coolant level, thermostat, and fan operation
  
• Drain and inspect hydraulic filters. Presence of metallic “glitter” indicates internal drive motor or piston pump wear and may require pressure/flow testing
  
  
• Disassemble and rebuild the steering/drive valve bank using a proper seal kit. Grease all O‑rings and confirm spool movement before reassembly
  
  
• Confirm hydraulic oil cleanliness and change if degraded. Flush suction and return lines if varnish or clogging is suspected.
  

Terminology and Component Definitions

• Steer/Drive Valve Bank: The hydraulic block that directs fluid to track drive motors and steering circuits. Contains multiple sections and spool valves.
  
• Seal Kit: A collection of O-rings, backup rings, and lip seals used when reassembling hydraulic valve sections and preventing internal bypass.
  
• Hydraulic Filter: A cartridge filter capturing metal debris, varnish, and contamination. Must be checked for shiny particles ("glitter") indicating wear.
  
• Pressure/Flow Test: Measurement of hydraulic pressure and volume output at the motors or pump against OEM specifications to verify correct performance.
  

Signs and Causes in Real-World Repairs
Instances of overheating were traced to plugged radiators—some pavers had clogged cores restricting airflow, leading to coolant circulation problems and thermostat failures. Proper cleaning and thermostat testing resolved persistent high-temperature alarms.

In another case, a drive motor failure was flagged by metallic wear in the hydraulic filter; replacement of the motor and subsequent pressure testing restored normal travel performance.

A more subtle issue involved installation of a steering valve seal kit. Without assembly grease, newly installed seals bound on the spool, causing stickiness and control lag. Proper lubrication and careful reassembly eliminated the fault.

Checklist of Steps to Resolve Issues

• Warm up the paver under load and note temperature behavior
  
• Inspect and test the fan, thermostat, coolant hoses, and radiator cleanliness
  
• Remove hydraulic filters, examine for fine metallic debris
  
• Rebuild or reseal steering/drive valve sections using the correct kit and lubrication
  
• Flush system suction and return paths if varnish or slugging is found
  
• Conduct pressure and flow tests on drive motors and pumps to compare against OEM specs
  
• Monitor hydraulic oil condition regularly and replace fluid/filter if contamination is detected
  

Supplementary Industry Tales
A municipal paving crew once faced repeated paver shutdowns mid-job due to overheating. The solution turned out to be a thermostat leaking overheat coolant while idle, causing latent airflow starvations downstream. A simple thermostat change and coolant flush restored reliable cooling.
Another contractor noticed reduced track speed and erratic steering; filters revealed glitter-like metal flakes. Replacing both drive motors and cleaning the filters eliminated drive slippage issues after pressure testing confirmed flow rates.
Conclusion: Restore Power and Temperature Control
While the Gehl 1648 is a proven asphalt paver, its common failures often stem from manageable causes—a clogged radiator, worn seals, contaminated hydraulic fluid, or subtle seal-pack installation mistakes. With a structured diagnostic routine, cleaning, resealing, and periodic testing, most issues can be resolved without major overhauls. Persistent failures are usually traceable through inspection of operating temperature trends, filter checks, and valve rebuilding.
Restoring performance is mostly about returning clean fluid, proper seal integrity, and effective coolant circulation—and knowing which component to fix first through careful observation.