Federal 4WD Models
- To test thermo vacuum valve, remove from engine and connect hoses to valve ports. Cool valve with water being careful not to submerge valve or allow water to enter valve ports or filter.
- With valve below 127°F (53°C), blow air into valve's bowl vent port and check that air flows out of top filter port and is blocked at lower port to intake manifold. See Fig 1 .
- Warm valve with hot water until valve is above 149°F (65°C). Seal port to bowl vent and blow air into valve's manifold vacuum port. Check that air flow is blocked with port sealed and that air flows freely out of port when opened.