Cooling System - Air or Combustion Gas Test (008-019)
B3.9 and B5.9 Series Engines
Section 8 - Cooling System - Group 08
If the color of the test fluid does not change from blue to
yellow during the 30-minute test period, return the engine
to low idle.
Check the test instrument to make sure that 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, combustion gases are
entering the cooling system. Further investigation is re-
quired 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 is the only indication of combus-
tion gas in the cooling system.