Hi.

I just bought an 04 civic EX and noticed I wasn't getting heat on idle. When car is running heat comes back. I noticed there were not enough coolant in the overflow reservoir so I added some and checked for air in the radiator (started the car, let it warm with the radiator cap off, etc...)

I don't have any overheating problem, the temp gauge stays right below the middle, but it's winter here and outside temp is around 0 since a few months.

Do you have any input to give me?

I thought

1) Thermostat stuck open. The car temp would not stay at operating temp when idling?

2) Bad head gasket? The car would overheat? But it's not. I let it ran idling for an hour or so...

3) Bad waterpump (not pumping enough coolant so it doesn't get to the heater core, but why is my heat coming back when the car is running?)

My upper rad hose is hot, the lower one is cold. (I think the upper hose is the hot coolant coming out the engine to the radiator while the bottom one shoots the cooled coolant to the engine block right?)

Thank you in advance... Having a hard time there during cold mornings.

 

https://honda-tech.com/honda-civic-2.../#post50222832

Did you bleed the cooling system?

 

Kind of, yes! But I didn't flush it completely. Simply warm the car and added coolant. I saw a few bubbles but nothing major.

It's pretty hard to do it right now since it's 0 F outside... Fan don't kick in often...

But why would an hose be cold and the other one hot then? It's not overheating at all.