I have a 98 civic ex. I had noticed the coolant was a little low so I filled radiator and coolant overflow. I drove for a few hours. when I shut it off and it was cooled down, I noticed the overflow had coolant on it and it overflowed onto the ground.

 

what could be causing this to happen?

 

it could be something as simple as a bad radiator cap thats where i would start first. is the car overheating ?. technically your not suppose to fill the overflow tank just the radiator its possible you added to much fluid.

 

I replaced rad cap. I noticed that the fluids were low so i filled it up and not knowing Hondas well i think i might have filled it too much. And when pressure was released it would push it out overflow

 

i think you overfilld the coolant system side note you never fill the overflow tank on any car not just a honda.

 

I had same problem on my 98 civic, Turned out to be head gasket blew inside and was lettin exhaust gas in cooling system

 

Fill the Radiator, make sure the engine is heated enough so that the thermostat is open. Make sure you have some coolant in the overflow. When fluid heats it expands, this will add to your overflow, when the engine cools, it draws that fluid back in, eliminating any air.