Radiator overflow tank keeps overflowing - where am I getting this wrong? Or is there some other issue at play?

[Insy]

Hello, I have just finished flushing the radiator on my 2009 SE5. After emptying the radiator and closing the bottom drain plug, I filled the radiator tank to the max mark with fresh antifreeze, left the cap off the reservoir tank, and started the engine. The temperature rose steadily and so did the level of antifreeze in the tank to the point of overflowing. While overflowing the level dropped suddenly and the overflow tank emptied.
Switched motor off, refilled the tank to the max mark and repeated the process with the same result. I have now run out of antifreeze which is soaking into the garage floor. Could someone please advise where I'm getting it wrong or let me know if there is some other issue at play. Thank you in advance.

 

[Peter Aawen]

See the threads in the 'Similar threads' block below the replies; &/or search on 'bleeding the cooling system' with the 'Search titles only' box ticked; or you could try just 'Bleeding', still with the 'Search titles only' box ticked, then search thru all the brake bleeding threads to find the cooling system threads; or maybe just search on 'Air Pockets' without the 'Search titles only' box ticked, only there's a lot of them to go thru too.

There's a LOT here on this, if you look.

 

[Mikey]

You are going to have to work the air out of the system and that means it's going to burp! Fill it slow and get the right-side front tire as high in the air as possible. There are a lot of ups and downs in the system and the air gets trapped in there, heat is what's going to push it out, keep the res full!