89CivicDX2door-Coolant overflow problem

Ever since I replaced the radiator, with the radiator coolant full, and the reservior bottle at MAX level, after driving and parking, see coolant on the floor. Upon examination, noticed that the reservior bottle is full upto the brim, and the radiator coolant level gone down. the coolant spill seems to be coming from the reservior bottle.

Once I keep the radiator coolant level down (by about 400 ml), and the reservior bottle at MAX, the system seems stabilized, with no overflow of coolant on the road.

Anyone has any insight as to why this happens?

Make sure that when you turn off the car that the overflow tank isn't bubbling. I've see that issue when the headgasket blows - it puts pressure in the system and causes the overflow thank to bubble and eventually overflow onto the ground.

Thanks 4G4D Store.
Checked. There is no bubbling.

If I do not fill the rad to the brim, noticed no overflow on ground, but the reservior tank still fills up over the max mark. this started happening ever since new rad was installed!!!

Not sure if related to Head Gasket: The oil is clean and normal. No unusual smoke. Car runs fine.

....Also one more thing. The car never heats up, and temp gauge always remain under and close to the middle.

Anyone please.
I want to be proactive, before anything happens. thanks.

I'd start with a new radiator cap and make sure the hose from the radiator to the overflow is new and has no cracks or isn't loose.

Does your thermostat gauge on your instrument cluster stay at running temperature when your car is started from cold? if so replace your thermostat.

With the car just started from cold, remover your rad cap. Fill radiator full if it will take more.

Fill your coolant resivour to inbetween the min/max mark. Allow engine to warm up fully. If your resivour fills to the point of over flow try replacing rad cap as stated if problem continues preform cylinder leakage test and listen of air excaping through coolant system (put your ear up to the radiator fill point) if you here air leakge replace cylinder head gasket.