This is normal. Water expands when heated and has to go somewhere...> =out the pipe.
Later radiators (eg Clubby) have a level indicator mark inside. Surprise surprise, it's about 1/2 way down the tank..
If you `could' (don't try this!) see inside the tank when it's hot, you would find it is full. The air gets sucked back in as it cools, this is normal too.
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
