expansion tank

I've changed the cylinder head on my 300tdi defender, brand new oem part, new valves etc. basically all new up top. But since I've filled the coolant up as I've replaced the tank with a clear one I can see that on tick over there's bubbles blowing from the smaller pipe closest the rad on the expansion tank, if I rev the engine it blows the coolant up in the tank as if you put a air line in the coolant. I presume its not meant to do the that, my neighbour (who's not a mechanic said its the water pump, pumping the coolant around). I don't want the take it out a I'm concerned it could damage the new head.
Also it seemed to get very hot, I know it gets hot but it seems very hot for a short journey.
I've search the internet but cant give any thing.

After its cooled down if you open the cap is it still pressurised?

The smaller pipes are air bleed pipes.

I'm not sure, I'll take it out this afternoon and see what happens.