Diesel Generators – Troubleshooting Cooling System Issues

Diesel Generators can have issues with the cooling systems.

Here we offer advice for what to check before calling an engineer.

Operator’s Maintenance
The most important link in the maintenance chain is the engine operator.  His daily and weekly checks of the cooling system and reports on any questionable conditions he observes will help prevent engine breakdown on the job and provide valuable information to engine repair people. Each must be recorded and reported as and when they are found.


Diesel Generator Checks Before Start-up

  1. Water level.
  2. Cleanliness of coolant.
  3. Radiator cap gasket.
  4. Hose and connections for leaks or hose collapse.
  5. Engine lubricating oil level.


Oil level too low or too high will cause overheating and possible loss of the coolant.

  1. Check for water in the oil and vice versa.
  2. Inspect the fan for bent or damaged blades.
  3. Similarly, check the belt for tension and condition.
  4. Inspect the radiator for bent core fins or accumulation of debris.
  5. Check shutters for damage or linkage wear.
  6. Equally important, check for leaks at the cooler, water pump, or other accessories.

Diesel Generator Coolant system issues, Complaints and Causes

Loss of coolant due to external leakage.

  1. Leaking pipe plugs, such as core plugs, which seal off coolant passages
  2. Loose clamps, faulty hose and piping.
  3. Leaking radiator:  Core hole plugs are sometimes loosened by corrosion or vibration.

These same conditions, or frozen coolant, can cause core seals to open up.

  1. Leaking radiator, de-aeration top tank or surge tank.
  2. Leaking gaskets due to improper tightening of cap screws, uneven gasket surfaces or
    faulty gasket installation.
  3. Leaking drain stop cocks.
  4. Leaking water pump:  Needless to say badly worn or deteriorated seals are the cause of leaks at the
    pump. Premature failure of the pump seals often results from suspended abrasive
    materials in the cooling system, or excessive heat from lack of coolant or cavitation.
  5. Leaks at engine cylinder head gasket.
  6. Leaks at upper cylinder liner counter bore.
  7. Leaking engine or auxiliary oil cooler.
  8. Air intake leaking after cooler (intake air heater in some cases).
  9. Water manifold leaking and/or connections.

Loss of Coolant Due to Internal Leakage

  1. Leaking engine cylinder head gasket:  Coolant passes into the cylinders or the crankcase.
  2. Cracked engine cylinder head:  Coolant passes into cylinders and is blown out of the
  3. Deteriorated, severed or chafed liner packing; defective liner packing bore:  Coolant
    passes into the engine crankcase.
  4. Improperly seated or defective sleeves:  Coolant can pass into the cylinder, crankcase,
    and, if the heads have cylindrical injectors, coolant can enter the fuel system if it gets
    past the injector body O-ring.
  5. Porous cylinder block or head casting:  Coolant can pass into the crank case via holes in
    the system jacket.  If the cylinder heads have internal fuel passages, coolant can
    enter the fuel system via holes in the wall of the fuel rifle which adjoins coolant passages
  6. Cracked or porous water cooled exhaust manifold and faulty manifold to head mounting
    gaskets.  Coolant passes into the cylinder or out through the exhaust system.
  7. Leaking engine or accessory oil cooler:  Coolant passes into the oil side of the cooler
    when the engine is shut down.  The reverse almost always occurs when the engine is
  8. Leaking engine air intake after cooler or intake air heater:  Coolant passes into the
    cylinders on naturally aspirated engines, also on turbo charged engines when the intake
    manifold pressure is less than the coolant pressure.

Loss of Coolant Due to Overflow

  1. Over filled radiator:  As the engine reaches normal operating temperatures, the coolant
    expands, and due to a lack of expansion space, unseats the pressure cap or relief valve,
    allowing the coolant to pass out through the overflow pipe.  This does not occur with a
    properly designed top tank – expansion space compensates for this.
  2. Slush freeze or frozen coolant resulting from insufficient antifreeze in the system or
    poor mixing of antifreeze and water.
  3. Dirt, scale or sludge in the cooling system.
  4. Plugged radiator core.
  5. Restriction or plugging of fill line due to routing and/or deterioration.
  6. Combustion gas entering the cooling system and displacing the coolant causing it to
  7. More water introduced in the area above the baffle than the fill line can handle
  8. Improperly routed or sized fill line.
  9. Also, excessive air intake temperatures.

Diesel Generator Engines Overheating

  1. Poor circulation of coolant caused by collapsing of soft hose and restriction.
  2. Over fuelling the engine.
  3. Radiator shutter malfunction or improper adjustment of the thermal controls.
  4. Incorrect adjustment or malfunction of variable pitch or modulating fans.
  5. Crankcase oil level too high:  Crankshaft dips in oil and causes a corresponding increase
    in temperatures due to friction and parasitic load on the engine.  Crankshaft oil dipping can
    also be encountered when operating an engine beyond the angles for which the oil pan was
    originally designed.
  6. Dirty engine exterior:  Heavy accumulations of dirt and grease can severely hinder normal
    heat dissipation through the exterior walls of all the engine components.

Pressure of air in the cooling system

The following are the most common causes of air entrapment:-

  1. Low coolant level due to leaking water pump or leaks at hose and/or coolant
  2. Leaking air intake after cooler.
  3. Leaking engine or air compressor cylinder head gasket.
  4. Improperly seated injector sleeve.

 Inadequate cooling capacity:

This condition can be the result of misapplication of one or
any combination of the following cooling system components:-

  1. Radiator
  2. Top Tank
  3. Surge Tank
  4. Fan
  5. Fan Shroud
  6. Water Pump
  7. Auxiliary Coolers
  8. Re-circulation Baffles
  9. Fan Speed
  10. After boil: Coolant boils and overflows after the engine is abruptly shut down following
  11. Heavy loading.
  12. Improper fan belt tension.

Coolant Contaminated with Combustion Gases

  1. Cracked cylinder head.
  2. Blown head gasket.
  3. Injector sleeves leaking.

Coolant Contaminated with Fuel Oil

  1. Injector sleeves leaking.
  2. Porous cylinder head casting:  The fuel enters the cooling system through holes in the wall
    of the fuel rifle which adjoins the coolant passages.

Diesel Generator -WATER PUMP

Coolant Circulates at High Pump Speed. Impeller damage is primarily caused by
corrosion and cavitation erosion.

  1. Excessive impeller to body clearance.
  2. Loose water pump drive belts.
  3. Impeller slipping on the shaft.
  4. Cracked impellers.

Fan or Water Pump Belts Break Prematurely

  1. Foreign material falls in drive.
  2. Shock or extreme overloads.
  3. Belt damaged on installation by localised stretching.
  4. Belts not properly matched.
  5. Pulley misaligned.
  6. Pulley nicked or rough.
  7. Guard or shield interfering during operation.

Engine Operates Too Hot or Overheats When Loaded and Coolant is Known to be at the Proper Level

  1. An altered horsepower rating of an engine or new engine installation which exceeds the
    original design of the cooling system.
  2. Clogged radiator air passages.
  3. Damaged radiator core fins.
  4. Heat exchanger element which contains heavy lime and scale deposits.
  5. Thermostat not opening fully.
  6. Fan shrouding missing, damaged, or improperly positioned with respect to the fan.
  7. Recirculation baffles on the sides of the radiator missing or damaged.
  8. Fan drive belts slip:  Impeller slips on the water pump shaft.
  9. Clogged coolant passages, radiator, and engine.
  10. Automatic radiator shutters faulty:  Shutters only open partially or open too late.
  11. Faulty thermatic or modulated fan drive:  Fan engages too late or operates too slowly.
  12. Variable pitch fan not working:  Fan operates with the blades at an insufficient pitch.

Diesel Generator Engine Coolant Temperature Too Low

  1. Thermostat stuck in open position, or malfunctions, to allow premature opening.
  2. Seal lip deteriorates and hardens allowing the coolant to bypass the closed
    thermostat and enter the radiator.
  3. Excessive bypassing of coolant to the radiator, with the thermostat closed and properly
  4. Engine is exposed to very low temperatures and high wind with a low load factor.
  5. Water through the core due to a leaking de-aeration baffle.

Diesel Generator Lack of Temperature Control or indicators?

  1. Defective Thermostat:  Thermostat fails to open at the proper coolant temperature range
    and/or does not open completely.
  2. Defective Thermostat Seal:  Coolant leaks by the seal and onto the water pump, therefore
    bypassing the radiator.
  3. Operating engine having a pressurised cooling system without a pressure cap, with a
    defective pressure cap or a defective self-contained relief valve.

Clogged Water Filter Element

  1. Contamination of the coolant caused by soluble oil, engine lube oil, engine fuel, or rust,
    scale and lime.
  2. Contamination of the cooling system with dirty fill or make-up coolant.
  3. Together with, use of anti-leak additive.

Corrosion, Rust and Scale Build-up Occurs in the Cooling System even after the Water Filter is Serviced Regularly

  1. Insufficient water filter capacity.
  2. Like wise, improper water filter installation.
  3. Careless servicing of the water filter.
  4. Aeration of the coolant:  Moreover, free oxygen and carbon dioxide contained in the air are highly

Rapid Loss of Proper PH Value and Inhibitor Level of Coolant

Dilution of the water filter concentration caused by too frequent adding of make-up coolant
to the cooling system.

Auxiliary Components

Oil overheats even though the cooling system has adequate capacity and is free of defects.

  1. Clogged or restricted oil cooler passages.
  2. Restricted oil cooler and return lines.
  3. Similarly, restricted oil cooler supply and discharge lines.

Low Oil Pressure

  1. Firstly, oil overheated.
  2. Improperly baffled oil cooler tube bundle.
  3. Also, low oil level.

Abnormal Sludging of the Engine Lube Oil Resulting in Oil Cooler Clogging

  1. Engine operates constantly at below normal coolant temperature or reaches the normal
    operating temperature too slowly.
  2. Additionally, antifreeze leaking into oil pan.

In short, a maintenance contract with a reliable company will avoid most of the above issues.

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