Centinel System – Repair Manual – 008-019   Cooling System – Air or Combustion Gas Test

WARNING  Do not remove the pressure cap from a hot engine. Wait until the coolant temperature is below 50°C [120°F] before removing the pressure cap. Heated coolant spray or steam can cause personal injury.

Allow the engine to cool and remove the radiator cap.

Check the coolant level according to the operator’s equipment manual recommendations and fill, if necessary.

Add heavy-duty coolant.
Refer to Procedure 018-004 (Coolant Recommendations and Specifications) in Section V, in the Signature and ISX Operation and Maintenance Manual, Bulletin 3666251.
Refer to Service Bulletin 3810340 for a description of heavy-duty coolants.

The pressure cap
must be tightly sealed in the top of the radiator fill neck.

Place the radiator cap back on and attach a rubber hose to the radiator overflow connection.

Place the free end of the hose below the water level in a container of water.

The engine coolant temperature
must be stable to perform this test. An increasing coolant temperature will give a false indication of air due to expansion of the coolant in the system.

Operate the engine at rated rpm until it reaches 82°C [180°F].

Check for a continuous flow of air bubbles from the hose into the water container.

A continuous flow of air bubbles can be caused by one of the following:

• An air compressor cylinder head leak. See the Leak Test – Air Compressor in this procedure.
• Fan, shutter, or heater air control thermostat valve leaking air. See the Leak Test – Fan, Shutter, or Heater Air Control Valve in this procedure.
• A cracked cylinder head.
  Refer to Procedure 002-004 (Cylinder Head) in Section 2.
• A cylinder head gasket combustion leak. See the Combustion Gas Leak – Overflow Method in this procedure.

If no air is found in the cooling system, do the following:

• Remove the test equipment.
• Operate the engine until it reaches 80°C [180°F], and check for coolant leaks.

Disconnect the vehicle air supply hose from the fan, the shutter, and the heater air control valve.

Install a plug into the air supply hose.

If the vehicle is equipped with more than one air control valve, check
only one valve at a time.

Start the engine and run for five minutes before testing for air in the coolant. This will allow any trapped air to purge from the system.

Repeat the test for air in the cooling system, as previously described.

If no air is found in the cooling system with the air control valve(s) isolated, install a new control valve.

Disconnect the coolant supply and the return tubes from the air compressor.

Use a short piece of hose to connect the tubes together to prevent coolant loss during engine operation.

Drain the air tanks completely to reduce the possibility of air entering the cooling system through the cab heater control valve.

Repeat the test for air in the cooling system as previously described in this procedure.

If no air is found in the cooling system with the air compressor isolated, repair or replace the air compressor.

Use combustion gas tester, Part Number 3822985 or its equivalent, to test for combustion gases in the cooling system.

A 50 percent antifreeze and 50 percent water mixture
must be used in the cooling system when performing the combustion gas leak test.

WARNING  Coolant is toxic. Keep away from children and pets. If not reused, dispose of in accordance with local environmental regulations.

NOTE: Coolant that gets into the combustion analyzer will stop the color change and render the test ineffective.

Drain the coolant level down approximately 75 mm [3 in] below the radiator cap seal ledge in the radiator fill neck.

Pour the test fluid into the combustion gas leak test instrument until it is up to the yellow fill line on the instrument.

Insert the rubber tip of the combustion gas leak test instrument into the radiator fill neck. Hold the instrument down firmly and turn back and forth to make sure that an airtight seal is formed between the tester and the radiator fill neck.

Start the engine and run at high idle for approximately 30 minutes. Monitor the engine temperature and color of the test fluid during engine operation. Do
not allow the engine temperature to exceed 100°C [212°F] during the test.

A flow of bubbles will occur as the engine warms up and coolant expands.

Bubbles in the combustion analyzer is
not a sign of a combustion leak.

If the color of the test fluid changes from blue to green or yellow any time during the test, combustion gases are leaking into the cooling system. Discontinue the test if the color of test fluid changes from blue to green or yellow.

If the color of the test fluid does
not change from blue to green or yellow during the 30-minute test period, return the engine to low idle.

Check the test instrument to make sure it is firmly sealed in the radiator fill neck.

Insert the tip of the rubber ball into the hole in the top of the test instrument. Squeeze the rubber ball 2 to 3 minutes to draw air from the radiator through the test fluid.

If the color of the test fluid remains blue, combustion gases are
not entering the cooling system. If the color of the test fluid changes from blue to green or yellow, combustion gases are entering the cooling system and further investigation is required to determine the source of the combustion leak.

As the cooling system warms up to operating temperature, air will be expelled through the combustion gas tester in the form of bubbles in the test fluid. This is due to normal expansion of the coolant. Do
not mistake the presence of air bubbles in the tester as combustion gases or air leaks into the cooling system. A change in the color of the test fluid from blue to green or yellow is the
only indication of combustion gas in the cooling system.

A positive result from the combustion gas leak tester indicates the following:

• Injector sleeve leakage. Be sure that the injector hold-down torque is correct.
  Refer to Procedure 006-026 (Injector) in Section 6.
• Cylinder liner protrusion
  not correct.
  Refer to Procedure 001-028 (Cylinder Liner) in Section 1.
• Cylinder head gasket or cylinder head casting leakage.
  Refer to Procedure 002-004 (Cylinder Head) in Section 2.
• Cracked cylinder liner.
  Refer to Procedure 001-028 (Cylinder Liner) in Section 1.

NOTE: Discard the tester fluid if it has indicated positive.

A negative result from the combustion gas leak tester, coupled with a continuous flow of air bubbles from the previous test, indicates the following:

• Defective fan, shutter, or heater air control valve.
• Air compressor head or head gasket leakage.
• Air entrained due to a bad radiator check valve or incorrect fill.

WARNING  Do not remove the pressure cap from a hot engine. Wait until the coolant temperature is below 50°C [120°F] before removing the pressure cap. Heated coolant spray or steam can cause personal injury.

Allow the engine to cool and remove the radiator cap.

Install a radiator pressure cap that has had the spring and the pressure relief valve removed to allow free flow from the overflow tube.

The pressure cap
must be tightly sealed in the top of the radiator fill neck.

Attach a rubber hose to the radiator overflow connection.

Put the free end of the hose below the water level in a container of water.

The engine coolant temperature
must be stable to perform this test. An increasing coolant temperature will give a false indication of air due to expansion of the coolant in the system.

Operate the engine at rated rpm until it reaches a temperature of 82°C [180°F].

Check for a continuous flow of air bubbles from the hose in the water container.