Rep Power: 0

2001 civic lx. installed funnel on radiator filler neck and kept it at least half full. ran engine till warm (fan came on at least twice) with the heater on high. left half full funnel on radiator overnight. reservoir between min and max. installed radiator cap the following morning. went to work, no problem noticed (seemed like system is not air-bound. parked overnight on level area. the following morning, reservoir about a quarter inch higher than before. drove with heater on high. noticed gargling sound in the heater core area. NOT LOSING COOLANT, THE COOLING SYSTEM JUST KEEPS ON GETTING AIR BOUND. ANY SUGGESTIONS? THANKS.

 
Rep Power: 0

First I would attempt to properly bleed the cooling system of air. You'll want to jack up the front of the car and repeat the funnel/coolamt process at the radiator neck to ensure you don't have air in the heater core. If coolant is still being forced into the overflow tank, I would replace the radiator cap because they do fail and they are the cheapest possible solution. Assuming all of your hoses are in good condition and air is still getting into the system, you probably have a leaking head gasket.