if on a 2004 Nissan frontier ,the water at normal temp.and you have the cap off on the radiator should it be flow water through the radiator if everything working properly.

  • Yes. Coolant flows if the pump is working and the thermostat is open.
    – SteveRacer
    May 3, 2019 at 1:28
  • 1
    It's very unlikely that the cooling system will work correctly if the cap is off the radiator. These systems are designed to work at elevated pressures in order to raise the boiling point of the coolant; with the cap off, no pressure will be developed, and the coolant will boil more quickly impairing the system's ability to function...and (hopefully not) erupting from the filler and scalding the operator. May 3, 2019 at 21:51

1 Answer 1


If the engine is at normal operating temperature, then you can't take the cap off, the system is designed to run at a pressure above atmospheric which raises the boiling point of the coolant above 100 degrees C.

If the system is pressurized and you remove the cap, then some of the coolant will explosively turn to vapor as it comes to equilibrium. This will normally blow a huge amount of wet vapor out of the system as the cap is removed - easily scalding anyone close.

Is the coolant mixture correct? Have you tried flushing the system? Or back-flushing the radiator? Have you tested the thermostat?

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