Combustion Leak Test
leak test is designed to check for the presence of combustion gases in the engine coolant.
It should be performed when signs (overheating, bubbles in the coolant, rise in coolant
level upon starting) point to a blown head gasket, cracked block, or cracked cylinder
tester, often called a combustion leak tester, is placed in the radiator filler neck. The
engine is started and the test bulb is squeezed and then released. This will pull air from
the radiator through the test fluid.
The fluid in
the block tester is normally blue. The chemicals in the exhaust gases cause a reaction in
the test fluid, changing its color. A combustion leak will turn the fluid yellow. If the
fluid remains blue, there is no combustion leak.
leakage into the cooling system is very damaging. Exhaust gases mix with the coolant and
form corrosive acids. The acids can cause holes in the radiator and corrode other
An exhaust gas
analyzer will also detect combustion pressure leakage into the coolant. By placing the
analyzer probe over the filler neck and accelerating the engine, the probe will pick up
any hydrocarbons (HC) leaking from the system, which indicates combustion leakage.