With engine running, place tester on coolant compensation tank. The air from the coolant compensation tank is sucked off by actuating the rubber bellows.
 Important! No coolant must be sucked off.
 Inspect If the blue liquid in the upper chamber of the tester turns yellow, the cylinder head seal and the cylinder head leak. Operation:
The transparent cylinder of the tester contains a blue reaction fluid which turns yellow when exposed to air which contains the slightest amounts of carbon monoxide. When the test fluid is exposed to fresh air, it regenerates, i.e. turns blue again. The fluid can be checked by exposing it to exhaust emissions from the exhaust pipe. The test fluid should then turn yellow. | 
