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280 Models (Calif.)

  1. Check for presence of vacuum at straight connection of the 63°F (17°C) thermo valve. If vacuum is present, thermo valve is operating properly.
  2. If no vacuum is felt, disconnect vacuum line from angular connection of the valve and check for vacuum at end of line. If vacuum is present, replace thermo valve. If no vacuum is felt, disconnect other end of vacuum line from intake manifold and blow out manifold vacuum port.
  3. Next, check operation of the 122°F (50°C) thermo valve in the same manner. Valve should be open with engine coolant temperature below 122°F (50°C) and closed with coolant temperature above 122°F (50°C). If not, replace thermo valve.
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