Reservoir fluid level goes down every time i fill it. Is this because the reservoir is overfilled?

Can anyone help me with this issue. I just bought a Honda Civic 2004 ex. I have a problem with the radiator fluid level. It always goes down and i have checked with compression test, there's no leakage and the radiator cap is good. But the other thing i'm concerned about is, the reservoir coolant tank is overfilled so will this effect the fluid level in reservoir. Every night i fill next day morning it goes down and there's no spills, is this because i overfill the reservoir with coolant.

Any suggestions would be greatly appreciated.

Thank you

Added (1). I mean, if the reservoir coolant tank is overfilled so will this effect the fluid level in radiator. Will it make it go down.

First check under your carpets on both sides as it could be a heater matrix leak, you can only fill it cold, if it has been refilled there will be air in the system which takes a few days or more to be expelled, put a pressure cap on the reservoir and leave it for 30 minutes, additional, it. Not really a reservoir it's and active part of the coolant circulation system

IF you DO overfill it, it WILL drain down, because it will overflow, when hot.

the level should be at the lower mark, when cold, and the higher mark when hot. IF you add coolant
when hot, and the level is already at the high level, it will then overflow.

So just keep it somewhere between the low mark and high mark, with it just above the low mark, when cold. (cold being when engine has not run for a few hours).

Otherwise, you might have a leak, as Harley suggests.

No. You have a small leak some where. I had a similar problem and it was a small crack in the seam of my radiator. Never enough to drip.

Thank you guys! Great Help! (Y)

A Honda car has a filling procedure and a bleeder valve.

Use the contents of the side tank to fill the radiator when performing the procedure.

Get your car at the appropriate angle, fill it, run and burp it,
bleed it.
Set the side tank level last.
A technician is supposed to do this.
I suggest going to one and getting it right.
ask all the questions you like from the tech while it is being tested and corrected, maintenanced etc.
Your water pump and hoses have a prevent mileage for
service at the time of your timing belt.
They can test your cap and related parts and explain it to you.
HAPPY HONDA.