coolant problem

[GTI NZ]

hi i have an 85' GTI 8v, every 2-3 days i have to keep tooping up the coolant as it seems to be disappearing, i have checked all hoses and they are fine, the tank where the coolant stays has a crack at the top, and when i open the bonnet after a drive, bubbles are coming out of the tank, and when the car has been driven for a while, or has been idling for a long time during the drive, the coolant starts to flow out of the crack spraying the stuff everywhere.
Whe the car idles, the coolant temperature rises above half, and when driving, the temperature goes back to half way. this has been going on for about a month, but i only used to have to top the coolant every 2-3weeks before.  this problem only started to occur when i changed the coolant about 3 months ago. Whats going on? is this serious? like a leaking head gasket? or is it just something minor, like maybe replacing the coolant tank?
any help muchly appreciated

[golfvr6]

If the tank has a crack in it then replace it! as you will be losing pressure.

[gozzy]

Defo a header tank, same thing happend to my 8V  and my coolant light was flashing all the time. You can pick them up from any scrappy. Mine is off an Audi 100. works great cost me 3 pound

[richandhazel]

They don't cost a lot to buy new..........you need to replace it as you are losing pressure and therefore lowering the boiling point of the coolant.