Tickover the water is pretty still and you can only see the water flowing in and out of the header tank, Its only when you increase the revs it starts bubbling, popping, farting, gurgling, makes some really unusual noises, the higher you rev it the more fierce it bubbles and the louder the noises get, then it spews over, just cant work it out as i did this yesterday when i first fitted the pump, then i let it cool topped it up ran it up again and it was fine, its not overheating though according to the guage, and when you turn it off once its warm it continues to gargle and burp for a minute or two and the water in the header shoots up and down.. really baffled me. Is there any bleed nipples on these anywhere?

Cheers