The terms "co tester kühlwasser" refer to a CO2 leak tester used for testing coolant (Kühlwasser in German) in vehicle engines. This tool helps detect combustion gases like carbon dioxide (CO2) in the cooling system, which can indicate leaks such as a blown head gasket (Zylinderkopfdichtung) or cracks in the engine block. The presence of exhaust gases in the coolant system leads to overheating and engine damage, so this test is vital for diagnosis. A CO2 tester kit typically includes a glass cylinder and a blue test liquid that changes color if CO2 is detected—for example, it turns yellow or green depending on engine type. The test requires a warm engine with the thermostat open; the tester is placed on the radiator or coolant reservoir opening. Gas bubbles appear if combustion gases leak into the cooling system, causing the test liquid to change color, which indicates a faulty head gasket or engine crack. These kits have advantages like ease of use without professional help, rapid results, and are suitable for all water-cooled engines. The test saves time and costly repairs by accurately diagnosing leaks early. In summary, a "co tester kühlwasser" is a diagnostic tool for detecting CO2 leaks in the coolant system, identifying engine damage that lets combustion gases mix with coolant, and helping prevent overheating-related failures.

Translation note: "Kühlwasser" means "coolant" in English.