Do not remove the pressure cap from a hot engine. Wait until the 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.
If one of the air control valves or the air compressor was not the source of air entering the cooling system, perform the combustion gas leak test outlined as outlined in this procedure.
The engine can overheat with the fan control or the shutter air control valve disconnected. Monitor the engine coolant temperature while performing this test. The coolant temperature must not exceed 100°C [212°F].
Disconnect the vehicle air supply hose to 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 in this procedure. If air is not found in the cooling system with the air control valve(s) isolated, install a new control valve.
The air compressor discharge line must be disconnected at the compressor to allow the compressor to discharge air to the atmosphere during this next test to prevent the compressor from overheating. Do not run the engine over five minutes with components isolated from the cooling system. Component damage can occur.
Repeat the test for air in the cooling system as previously described in the air in the cooling system test. If air is not found in the cooling system, with the air compressor isolated, repair or replace the air compressor. Refer to Procedure 012-014.
Perform the air in the cooling system test outlined in this procedure.
If the engine still fails the test for air in the cooling system with the fan, shutter controls, and the air compressor isolated from the cooling system, or if the combustion leak test is positive, pressure check the cylinder heads. Refer to Procedure 002-004.
An optional method of testing is to use the combustion gas tester, Part Number 3822985, or its equivalent to test for combustion gases in the cooling system.
It is recommended that the cooling system contain a mixture of 50 percent antifreeze and 50 percent water during the combustion gas leak test.
The use of water only can result in a color change in the test fluid from blue to turquoise or light green during the test. This is not an indication of a combustion gas leak.
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 air tight seal is formed between the tester and 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 yellow, combustion gases are entering the cooling system.
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 because 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 yellow is the only indication of combustion gas in the cooling system.
Do not remove the pressure cap from a hot engine. Wait until the 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.
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.
The cooling system diagnostic kit, Part Number 3822994, contains a sight glass and can be used to detect air or combustion gases in the cooling system.
Do not remove the pressure cap from a hot engine. Wait until the temperature is below 50°C [120°F] before removing the pressure cap. Heated coolant spray or steam can cause personal injury.
Loosen the radiator cap to prevent any pressure buildup in the top tank.
Hello, I'm Jack, a diesel engine fan and a blogger. I write about how to fix and improve diesel engines, from cars to trucks to generators. I also review the newest models and innovations in the diesel market. If you are interested in learning more about diesel engines, check out my blog and leave your feedback.
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