Service Manual

ISB, ISBe and QSB (Common Rail [...] Cooling System Diagnostics
Section 8 - Cooling System - Group 08 Page 8-55
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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 gas in the cooling system.