The cooling system controls engine temperature by circulating coolant through the cylinder block, cylinder head, radiator and associated components. Problems with coolant flow, pressure, airflow or combustion-gas leakage can cause overheating, poor heater performance, coolant loss or serious engine damage.
Coolant type, concentration, thermostat temperature, pressure-cap rating, belt tension and wet-liner requirements are engine-specific. Use the correct operator or workshop manual for the exact engine and serial range.
1. Main Cooling-System Components
A typical liquid-cooled diesel engine may use:
- Radiator
- Water pump
- Thermostat
- Cooling fan
- Pressure cap
- Expansion tank
- Coolant hoses
- Engine oil cooler
- Cab heater circuit
2. Coolant Flow
The water pump circulates coolant through the engine and radiator.
The flow path varies by engine, but normally includes:
- Cylinder block
- Cylinder head
- Thermostat housing
- Radiator
- Pump inlet
3. Thermostat Operation
When the engine is cold, the thermostat restricts flow through the radiator so the engine warms quickly.
As coolant reaches the specified temperature, the thermostat opens and allows greater radiator flow.
4. Thermostat Stuck Closed
Possible symptoms include:
- Rapid overheating
- Top hose becoming very hot
- Little or no radiator circulation
- Coolant boiling
5. Thermostat Stuck Open
Possible symptoms include:
- Slow warm-up
- Low operating temperature
- Poor cab heat
- Increased fuel consumption on some engines
6. Do Not Remove the Thermostat as a Permanent Repair
Removing the thermostat can cause:
- Incorrect coolant flow
- Slow warm-up
- Poor temperature control
- Hot spots on some engine designs
Opening temperature and bypass design matter. A thermostat that physically fits may still be wrong for the engine.
7. Water Pump
The water pump may be driven by:
- Fan belt
- Serpentine belt
- Timing gears
- Timing belt
8. Water-Pump Failure Symptoms
Possible signs include:
- Coolant leak from weep hole
- Bearing noise
- Pulley play
- Poor circulation
- Overheating
9. Water-Pump Impeller Damage
A pump can turn normally but circulate poorly if the impeller is:
- Corroded
- Loose on shaft
- Damaged
- Incorrect replacement type
10. Radiator
The radiator removes heat from coolant using airflow through its core.
Problems may include:
- External dirt blockage
- Internal scale
- Damaged fins
- Coolant leaks
11. Clean the Radiator Properly
Construction and agricultural machines often collect:
- Chaff
- Dust
- Mud
- Oil contamination
Clean from the correct direction and avoid damaging fins with excessive pressure.
12. Radiator Pressure Cap
The pressure cap raises cooling-system boiling point by maintaining controlled pressure.
A weak cap can cause:
- Coolant loss
- Early boiling
- Overflow
13. Never Open a Hot Cooling System Carelessly
Hot coolant can remain under pressure. Allow the engine to cool and follow the manufacturer’s procedure before removing the cap.
14. Expansion Tank
Some systems use a pressurised or non-pressurised expansion/recovery tank.
Check:
- Correct cold level
- Cap condition
- Return hose
- Cracks or leaks
15. Cooling Fans
Fans may be:
- Direct belt driven
- Viscous-coupled
- Hydraulically driven
- Electrically driven
16. Viscous Fan Clutch
A weak viscous coupling can cause overheating under load while temperature appears acceptable at light load.
17. Hydraulic or Electric Fan Faults
Possible causes include:
- Temperature sensor fault
- Solenoid fault
- Controller command fault
- Hydraulic motor problem
- Electrical relay/fuse fault
18. Coolant Hoses
Inspect hoses for:
- Cracks
- Softening
- Bulges
- Oil damage
- Loose clamps
- Internal collapse
19. Collapsed Lower Radiator Hose
A weak hose can collapse under pump suction and restrict coolant flow, especially at higher engine speed.
20. Correct Coolant
Coolant must provide:
- Freeze protection
- Boiling protection
- Corrosion protection
- Cavitation protection
Do not assume all antifreeze types can be mixed.
21. Water Quality
Where coolant is mixed from concentrate, water quality matters.
Hard or contaminated water can contribute to:
- Scale
- Corrosion
- Reduced heat transfer
22. Wet-Liner Engines
Many agricultural and industrial diesels use wet cylinder liners directly surrounded by coolant.
These engines can be vulnerable to liner cavitation.
23. Wet-Liner Cavitation
Rapid liner vibration can create tiny vapour bubbles that collapse against the liner wall.
Over time this can cause:
- Pitting
- Pinholes
- Coolant entering cylinder or sump
24. Cavitation Protection
Use the exact coolant chemistry required by the engine manufacturer.
Some engines require:
- Specific inhibitor package
- Supplemental coolant additive
- Extended-life coolant
25. Coolant in Engine Oil
Possible causes include:
- Wet-liner seals
- Liner cavitation
- Head gasket
- Cracked head/block
- Oil cooler failure
Do not continue running the engine with coolant-contaminated oil.
26. Combustion Gas in Cooling System
Possible signs include:
- Rapid pressure build-up from cold
- Repeated coolant loss
- Continuous bubbling
- Hard hoses soon after starting
Possible causes include head gasket, cracked head or liner sealing problems.
27. Engine Overheats Only Under Load
Check:
- Radiator airflow
- Fan operation
- Coolant flow
- Thermostat
- Fuel/boost condition
- Head-gasket leakage
28. Engine Runs Too Cool
Possible causes include:
- Thermostat stuck open
- Incorrect thermostat
- Temperature sensor fault
- Fan operating continuously on controlled systems
29. Best Cooling-System Diagnostic Order
- Check coolant level and condition.
- Check radiator cleanliness and airflow.
- Inspect belts, fan and hoses.
- Check thermostat operation.
- Check water-pump condition and circulation.
- Pressure-test system and cap if required.
- Check for combustion-gas leakage if symptoms persist.
- Investigate liners, head gasket or internal faults only after external checks.
30. Cooling-System Checklist
| Area | Check |
|---|---|
| Coolant | Correct type, concentration and level. |
| Radiator | Clean externally and flowing internally. |
| Thermostat | Correct type and opening behaviour. |
| Water pump | No leaks, play or poor circulation. |
| Fan | Operating correctly under load. |
| Hoses | No collapse, cracks or leakage. |
| Pressure cap | Correct rating and holding pressure. |
| Wet liners | Correct coolant protection used. |
| Manual data | Exact engine-specific specifications followed. |
Related Agrimanual Manuals
Cooling-system layout, thermostat values, coolant specifications and wet-liner requirements are engine-specific.
- Search Agrimanual engine workshop manuals
- Search Agrimanual diesel engine cooling manuals
- Request a manual if your engine is not listed
Frequently Asked Questions
Can a thermostat cause overheating?
Yes. A thermostat stuck closed or only partly opening can severely restrict radiator flow.
Can removing the thermostat cure overheating?
It may temporarily alter symptoms, but it is not a correct permanent repair and can upset coolant flow on some engines.
Why does an engine overheat only when working hard?
Restricted radiator airflow, weak fan operation, poor coolant flow, boost/fuelling problems or combustion-gas leakage are common possibilities.
Why is coolant getting into the sump on a wet-liner engine?
Possible causes include liner O-rings, liner cavitation, head-gasket failure or cracked components.
Can I use any antifreeze in a diesel engine?
No. Use the coolant chemistry and concentration specified for the engine, particularly on wet-liner engines.
Cooling problems should be diagnosed from the outside inward: coolant, airflow, thermostat, pump and pressure before assuming major internal engine damage.