Solving Persistent Overheating in the 1986 International TD8E Dozer

[MikePhua]

The TD8E and International Harvester’s Compact Crawler Legacy
The International TD8E was part of a lineage of compact crawler tractors developed by International Harvester during the 1970s and 1980s. Designed for light-to-medium earthmoving, land clearing, and site prep, the TD8E featured a DT239 diesel engine—a naturally aspirated inline-four known for its torque and simplicity. With an operating weight around 16,000 lbs and a power output near 70 hp, the TD8E was widely used by contractors, farmers, and municipalities across North America.
International Harvester, later restructured into Navistar, had a strong reputation for building durable machines with mechanical drivetrains and straightforward serviceability. The TD8E was no exception, but like many older crawlers, it can develop chronic overheating issues if cooling system components degrade or airflow is compromised.
Progressive Overheating and Initial Repairs
A common scenario involves a TD8E that initially runs well but begins to overheat progressively—first after an hour, then within 30 minutes of operation. This pattern suggests a gradual decline in cooling efficiency rather than a catastrophic failure. In one case, the operator had already logged 120 hours before noticing the temperature creeping upward.
Initial repairs often include:

• Replacing the valve cover gasket and muffler
  
• Flushing the cooling system with chemical cleaners
  
• Installing a new thermostat and water pump
  
• Inspecting and replacing coolant hoses
  
• Cleaning radiator fins with compressed air
  

Despite these efforts, overheating may persist, indicating deeper issues with airflow dynamics, radiator core efficiency, or gauge accuracy.
Fan Orientation and Airflow Direction
One overlooked factor is the radiator fan’s orientation. On most dozers, the fan is designed to push air forward through the radiator, away from the engine. This prevents dust and debris stirred up by the blade from clogging the radiator core. If the fan is installed backward, it may still rotate correctly but move significantly less air, reducing cooling capacity.
Key points:

• Fan blades should curve toward the engine, scooping air forward
  
• Rotation direction (counterclockwise from the operator’s seat) must match blade pitch
  
• The fan should be positioned deep within the shroud for optimal airflow
  
• A spacer may be needed to bury the fan into the shroud without contacting the radiator
  

In one case, the fan was mounted too shallow, reducing its ability to draw air through the radiator. After repositioning and cleaning the fins thoroughly, the machine ran cooler for longer periods.
Radiator Core Efficiency and Temperature Differentials
A healthy radiator should show a temperature drop of 10–20°F between the top and bottom hoses. If both hoses read nearly the same temperature, coolant may not be flowing effectively through the core. This could be due to internal scaling, partial blockage, or insufficient airflow.
Recommended steps:

• Use a laser thermometer to measure top and bottom hose temperatures
  
• Backflush the radiator with a garden hose and compressed air
  
• Inspect for sediment discharge and repeat until water runs clear
  
• Confirm that the thermostat opens fully at the rated temperature (usually 180–195°F)
  

In one field test, the top of the radiator read 190°F while the bottom was only 170°F after cleaning—indicating improved heat exchange. Before cleaning, both readings hovered around 200°F, suggesting poor circulation.
Thermostat Installation and Coolant Compatibility
Thermostats must be installed with the copper capsule facing the engine block. Installing it backward can prevent proper operation. Additionally, coolant types should not be mixed. If the original coolant was green and the replacement is yellow, ensure full flushing to avoid chemical incompatibility.
Tips:

• Use a deep-fry thermometer to verify coolant temperature inside the radiator
  
• Confirm that all hoses contain the same coolant color post-flush
  
• Check for air pockets by running the engine with the cap off until the thermostat opens
  

In one case, the operator used a laser thermometer and confirmed that the block, thermostat housing, and water pump were all within 210–220°F, while the radiator coolant was only 190°F—suggesting partial circulation.
Fuel System and Combustion Considerations
Overheating can also stem from combustion inefficiencies. A leaking head gasket, advanced timing, or poor fuel atomization may increase exhaust temperatures and load on the cooling system. The DT239 engine does not use a thermostart unit, but starting fluid dependency may indicate low compression or injector issues.
Recommendations:

• Perform a valve lash adjustment if history is unknown
  
• Inspect injectors for spray pattern and leakage
  
• Check for exhaust smoke under load (white = coolant, black = fuel, blue = oil)
  
• Verify timing and cold start advance settings
  

In one case, the engine required starting fluid even when warm, suggesting poor combustion. After adjusting valves and replacing fuel filters, starting improved and operating temperatures stabilized.
Gauge Accuracy and Sensor Validation
Mechanical temperature gauges can drift over time. If the gauge reads hot but infrared measurements show acceptable temperatures, the sensor or gauge may be faulty.
Validation steps:

• Compare gauge reading with infrared thermometer at multiple engine points
  
• Measure coolant directly inside the radiator with a probe thermometer
  
• Replace the gauge or sensor if discrepancies exceed 20°F
  

In one example, the gauge indicated overheating at 230°F, but actual coolant temperature was 190°F. Replacing the gauge resolved the false alarm.
Conclusion
Overheating in the International TD8E is often a cumulative issue involving airflow restriction, radiator inefficiency, fan misalignment, and combustion irregularities. By methodically inspecting each subsystem—cooling, fuel, airflow, and instrumentation—operators can restore reliable performance. The TD8E may be decades old, but with proper care, it remains a capable machine. In the world of legacy dozers, overheating is not a death sentence—it’s a diagnostic puzzle waiting to be solved.