7 hours ago
The Problem: Heat Buildup Under Load
Overheating in diesel-powered skid steers—especially older models like the 1982 Koehring 2150 Skat Trak equipped with a 60 hp Kubota inline six-cylinder engine—is a common but often elusive issue. In one case, the machine ran fine at idle and light load, maintaining temperatures around 150–160°F. However, after 15 minutes of moderate to heavy work, the temperature climbed past 200°F, eventually triggering coolant overflow after shutdown. Despite good power and no visible exhaust anomalies, the overheating persisted.
This scenario is emblematic of deeper thermal inefficiencies, often masked by seemingly normal operation.
Understanding Diesel Cooling Dynamics
Diesel engines rely on a closed-loop cooling system to regulate temperature. Key components include:
Terminology Note: Heat Soak and Coolant Puke
In the case at hand, the technician took several logical steps:
Field Anecdote: The Timing Trap
In a similar case involving a rebuilt injection pump on a diesel loader, the technician mistakenly used the wrong timing mark during reinstallation. The result? Advanced injection timing caused incomplete combustion and elevated exhaust temperatures, which radiated back into the cooling system. The error was only 3–4 degrees, but it led to chronic overheating until corrected.
This underscores the importance of verifying injection timing—especially after pump service.
Diagnostic Checklist for Diesel Overheating
To systematically diagnose overheating, consider the following:
If standard repairs don’t resolve the issue, consider these less obvious culprits:
In the original case, installing a larger aluminum radiator resolved the issue. Operating temperatures stabilized at 180–190°F, even under load. This confirmed that the original radiator lacked sufficient capacity for the machine’s thermal output.
Conclusion: Cooling Is a System, Not a Component
Overheating in diesel skid steers is rarely caused by a single failure. It’s a cumulative result of airflow dynamics, combustion efficiency, coolant flow, and heat exchange. By approaching the problem holistically—combining mechanical inspection with thermal logic—technicians can avoid chasing symptoms and instead solve the root cause. Whether you're working with a vintage Koehring or a modern compact loader, the principles remain the same: cool the engine, not just the symptoms.
Overheating in diesel-powered skid steers—especially older models like the 1982 Koehring 2150 Skat Trak equipped with a 60 hp Kubota inline six-cylinder engine—is a common but often elusive issue. In one case, the machine ran fine at idle and light load, maintaining temperatures around 150–160°F. However, after 15 minutes of moderate to heavy work, the temperature climbed past 200°F, eventually triggering coolant overflow after shutdown. Despite good power and no visible exhaust anomalies, the overheating persisted.
This scenario is emblematic of deeper thermal inefficiencies, often masked by seemingly normal operation.
Understanding Diesel Cooling Dynamics
Diesel engines rely on a closed-loop cooling system to regulate temperature. Key components include:
- Radiator (heat exchanger)
- Water pump (circulates coolant)
- Thermostat (regulates flow based on temperature)
- Fan (draws air through radiator fins)
- Overflow reservoir and pressure cap
Terminology Note: Heat Soak and Coolant Puke
- Heat Soak: The phenomenon where engine components continue to absorb and radiate heat after shutdown, often causing a spike in coolant temperature.
- Coolant Puke: Informal term for coolant being expelled through the overflow tube due to pressure buildup or boiling.
In the case at hand, the technician took several logical steps:
- Removed and flow-tested the original radiator—results were inconclusive.
- Installed a new Kubota water pump and thermostat—improved idle cooling but not under load.
- Ordered a larger aluminum radiator to maximize heat dissipation.
Field Anecdote: The Timing Trap
In a similar case involving a rebuilt injection pump on a diesel loader, the technician mistakenly used the wrong timing mark during reinstallation. The result? Advanced injection timing caused incomplete combustion and elevated exhaust temperatures, which radiated back into the cooling system. The error was only 3–4 degrees, but it led to chronic overheating until corrected.
This underscores the importance of verifying injection timing—especially after pump service.
Diagnostic Checklist for Diesel Overheating
To systematically diagnose overheating, consider the following:
- Verify coolant level and condition (look for contamination or air pockets)
- Inspect radiator fins for blockage or damage
- Confirm fan direction and airflow volume
- Check thermostat operation in hot water (should open around 180–190°F)
- Test water pump flow (look for impeller wear or cavitation)
- Use block tester to detect exhaust gases in coolant (head gasket failure)
- Inspect injection timing and pump calibration
- Look for external heat sources near radiator (e.g., exhaust leaks)
- Normal operating temperature: 180–195°F
- Coolant pressure cap rating: 13–16 psi
- Fan airflow: 2,000–3,000 CFM minimum
- Thermostat opening temperature: 180°F
- Radiator core flow rate: ≥ 20 GPM
If standard repairs don’t resolve the issue, consider these less obvious culprits:
- Cracked cylinder head allowing combustion gases into coolant
- Warped head from previous overheating
- Exhaust leak near radiator causing heat saturation
- Undersized radiator for engine output
- Airlock in cooling system preventing full circulation
- Pressure testing the cooling system
- Upgrading to multi-pass aluminum radiator
- Installing auxiliary cooling fans
- Replacing head gasket or resurfacing head
- Rechecking injection timing with dial indicator
In the original case, installing a larger aluminum radiator resolved the issue. Operating temperatures stabilized at 180–190°F, even under load. This confirmed that the original radiator lacked sufficient capacity for the machine’s thermal output.
Conclusion: Cooling Is a System, Not a Component
Overheating in diesel skid steers is rarely caused by a single failure. It’s a cumulative result of airflow dynamics, combustion efficiency, coolant flow, and heat exchange. By approaching the problem holistically—combining mechanical inspection with thermal logic—technicians can avoid chasing symptoms and instead solve the root cause. Whether you're working with a vintage Koehring or a modern compact loader, the principles remain the same: cool the engine, not just the symptoms.
