What's wrong when water doesn't flow from your radiator. I already put a water pump and a thermostat on putits still running hot. What could be the problem?

  • What evidence do you have that the engine is running hot, e.g Dash temp gauge, Electric Fans switching on, OBD2 parameters, boiling coolant, tested coolant temperature?
    – HandyHowie
    Commented Feb 18, 2016 at 12:04
  • Do your cooling fans kick on? Does the heater work? Does the radiator feel warm when the engine is hot? Did you remember to have the heater on when you re-filled the radiator? How the did coolant look when you drained it?
    – TMN
    Commented Feb 19, 2016 at 14:07

1 Answer 1


If there is no/insufficient coolant flow in the cooling system then there are a few options:

  • There is insufficient coolant in the system (check the coolant level);
  • It's flowing out of the system (probably on the ground);
  • The thermostat is stuck closed (it's defective and needs replacement);
  • The water pump is not doing it's job (it's defective or not connected to a belt);
  • A part of the cooling system is clogged (radiator or piping);
  • There is air in the cooling system (cause of improper air purging after refilling drained coolant) - thanks to Tim B for reminding about this one.
  • I think you've covered all bases, though I'm not sure if coolant flow would be completely stopped by a stuck-closed thermostat.
    – Zaid
    Commented Feb 18, 2016 at 10:14
  • @Zaid we talked about that aready, I believe. Coolant flow would be limited to the small circle only, mostly inside the engine. I still believe that no coolant should be able to get through to the radiator at all in the case of a closed thermostat. Commented Feb 18, 2016 at 10:23
  • 1
    Another possibility is that the cooling system was not sufficiently purged of air after the water pump and thermostat were replaced.
    – Tim B
    Commented Feb 18, 2016 at 20:00
  • @Tim B you're right, totally forgot that one Commented Feb 19, 2016 at 7:37

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