My honda civic is overheating and water is bubbling into the overfill tank, and then leaking out. I already replaced radiator and thermostat and there seems to be no pressure from the lower radiator hose to the thermostat. The electric fan fails to come on when temperature is high. Replaced themosensor, and that didn't change fan. The fan runs when connected to a 12 volt power. Could it be fan relay, water pump. Or head gasket? There is a lot of steam pressure into the overflow tank when car overheats.

Thanks. elmer

I am not familiar enough with Hondas to understand some of your details. The thermostat is near the lower radiator hose? Did you check the hoses when you changed the radiator? A bad hose can cut off circulation.

Does the exhaust have a sweetish smell? If so, it means coolant is leaking through a bad head gasket.

Most likely a thermostat, cheap and quick to fix. Or a collapsed hose. Depends on the model because some hoses have supports inside the hose, but I'm leaning mostly to the thermostat. The thermostat controls basically the flow and keeps the engine at a certain temp. now when they fail they are made to fail open so the coolent will flow continuously, but that overheats the engine after a coupl hours of driving, sometimes they stick closed and they stop all flow and the engine heats up very quickly, but its stuck open. Cheap 5 to either 7 dollar part most of the time if they are expensive. Or you could have put the thermostat in backwards. In that case you would not get crap considered to pressure. And if its your fans well, could be a relay to the thermosensor. Sometimes parts you get new are not always working. So have that checked as well.

I am having the same problem with my sisters honda... I have replaced the thermostat and sensor,but car still overheats after a few minutes of driving then starts to studder,I know that's due to the aluminum block swelling cause of heat but I can't find the original problem,if anyone has anymore ideas let me know... and no there isn't any colant in oil... only smokes a bit right at start!