Passat L4-1984cc 2.0L DOHC (1991)
Thermo-Vacuum Valve: Testing and Inspection
ON VEHICLE TEST
With the engine cold:
1.
Connect a hand operated vacuum pump to the thermo-vacuum valve (located in the upper coolant hose outlet, on the cylinder head).
2.
Apply 300 mm (12 in.) Hg vacuum to either side of the thermo-switch.
3.
With the engine COLD, thermo-vacuum valve must hold vacuum. If the valve leaks, replace it.
4.
Start the engine and let it reach normal operating temperature.
5.
With the engine warm (coolant fan should cycle on and off once):
6.
Both thermo-vacuum valve ports should be open, (the valve should not hold vacuum).
If the valve is blocked, replace it.
Fig. 38 Vacuum Thermo-switch, 16V (California)
OFF VEHICLE TEST
1.
Remove the thermo-vacuum valve from the engine, and use a water bath to warm or cool the valve to the proper testing temperature.
2.
Attach a piece of vacuum hose to the valve and blow air through it.
Below 27°C (81°F), the valve should be closed.
Above 49°C (120°F), the valve should be open.
3.
Replace valve if it is not within specification.