420SEL (126.035) V8-4.2L (116.965) (1986)
Mono Valve
9.
Carefully check the mono valve for pulsating action (by touch):
The mono valve should be heard or felt to pulse (frequency may vary). Also, the coolant hoses at both sides of the valve should be hot.
WARNING:This should be a momentary test. The technician should be aware that the heated coolant at the mono valve may cause burns.
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If the valve does not pulse, replace the mono valve.
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If the valve pulsates but hot coolant is not present at both sides of the valve, the valve may be plugged or defective. Replace or repair as
necessary.