Problem with rabbit engine in bug

[Daggis]

I thought I was done converting to the rabbit gti engine today, but no, as I was starting the engine, everything seemed to be working well, but as the water heated up, it expanded to much, and pourde out of the expansion tank, which I have inside the car..

So I'm wondering if I'm using a too little exp. tank, or if it's a wrong one. I'm using one from a peugeot 205, should be about the same size as the rabbit one, or even bigger. But this 205 tank only had one hole, so I drilled another one for the hose from the rabbit radiator. Is there supposed to be pressure in this tank? So that when I cut that hole, and it is not sealed, there is not pressure, and the water gets to expand freely? Or is it supposed to expand freely?

But I can't understand how approx. 7 litres of water can expand by like 1.5 litres?

[boygenius]

Does the expansion tank or the radiator have the pressure cap.

[Rob]

I'm just guessing here, but can it be that there is air in the cooling system ?
Doesn't air expand more than water (when heated) ?

Rob.

[Daggis]

I guess theres plenty of air in there..
The pressure cap is on the expansion tank.

That is a pressurized sealed cooling system. You should use the correct expansion tank and psi cap so it can do just that, expand. First get the right tank and go from there, you could have air in the system and/or depending on how the pipes and hoses are arranged there could be steam pockets if the layout is not correct. Also, the tank should not be inside the car. Do you have pictures so I can see how it's set up? That would help.