Chevrolet Cobalt Service & Repair Manual: Cooling System Pressure, Test

Caution: To avoid danger of being burned, do not remove radiator cap while engine and radiator are still hot, as fluid and steam can be blown out under pressure.
If radiator cap has contamination, rinse it with water.
Before using a radiator pressure tester, wet relief valve and pressure valve with engine coolant or water.
When performing pressure tests, keep tester at an angle of over 30° above horizontal.
Refer to published specifications to determine proper cooling system operating pressures.
1. Remove radiator cap.
2. Attach cap to radiator pressure tester.
3. Slowly pump tester and verify that air is coming from vacuum valve. Push pump at constant speed.
4. Pump tester quickly, about a one second push, and measure relief valve opening pressure. Compare opening pressure to pressure listed on cap. Refer to Fig. 1 for cooling system pressure range chart.
5. Remove pressure tester from cap.
6. Fill radiator and overflow to proper level with coolant.
7. Inspect overflow tube and overflow bottle for dents, kinks, or internal obstructions.
8. Wipe out inside of filler neck. Inspect lower inside sealing seat of filler neck for nicks, dirt and solder bumps.
9. Inspect cams on outside of filler neck. If cams are bent down or up, seating of pressure cap valve and tester seal will be affected. If cams are damaged, have filler neck replaced by a reputable radiator repair service facility.
10. Attach a radiator pressure tester and rotate tester head until locking ears contact stops on radiator.
11. Operate pump until indicator on gauge reaches just beyond color band for recommended pressure for vehicle, Fig. 1.
12. Verify that pressure does not drop. If pressure drops, inspect hoses, radiator or water pump for leaks. If no external leaks are found and pressure drops, inspect heater core, cylinder block and head.
13. Remove tester and install radiator cap.

Fig. 1 Cooling system pressure chart

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