Mitsubishi 6M60-TL Service Manual page 226

(2) Inspection of vent valve
• Note the coolant level in the reservoir tank.
• Start the engine and run it at high speed until the coolant level in
the reservoir tank has risen to a certain degree. Stop the engine.
• Allow the system to cool down. When the coolant temperature
has dropped to the atmospheric temperature, check if the cool-
ant level in the reservoir tank has subsided to the original level
noted earlier.
• If not, the vent valve is deemed faulty. Replace the pressure cap.
CAUTION
• If the pressure cap is opened before the coolant tempera-
ture drops to the atmospheric temperature, the negative
pressure in the radiator is canceled out. As a result, it is no
longer possible for coolant to flow into the reservoir tank.
Ensure that this does not happen.
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