Use a combustion gas tester, Part Number 3822985 or 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.
Drain the coolant level down approximately 76 mm [3 in] below the radiator cap seal ledge in the radiator fill neck.
If the coolant is above this point, the coolant can contaminate the test fluid, causing the test to be ineffective.
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 it back and forth to make certain that an airtight seal is formed between the tester and the
radiator fill neck.
NOTE: Install the test equipment at the expansion tank filler neck on Marine applications.
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 100ยฐC [212ยฐF] during the test.
If the color of the test fluid changes from blue to yellow or green anytime during the test, combustion gases are
leaking into the cooling system. Discontinue the test if the color of test fluid changes from blue to yellow or green.
If the color of the test fluid does not change from blue to yellow or green 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 yellow or green, 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 yellow or green is the only indication of combustion gases in the cooling system.
A positive result from the combustion gas leak tester indicates cylinder head gasket or cylinder head casting
leakage. Refer to Procedure 002-004 in Section 2.
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:
โข Damaged fan, shutter, or heater air control valve
โข Air compressor head or head gasket leakage
โข Air entrained due to a damaged radiator check valve or incorrect fill.
