Hi
Sounds like its a problem with the water bypass hose if it has a small 10mm tee connection that connects to a metal tube leading to the turbo.Easy to change.Remove air filter ducting for access,undo the 3 jubilee clips on the hose and remove it,expect a fair amount of water to pour out.Give ends of water connections a good clean to remove any gunge.I found it easier to put the two large jubilee clips over the new hose and the small clip over the thin metal pipe,apply a small amount of washing up liquid to the inside of the new hose connections,slides on easier.Push hose fully onto large connections first,then small pipe connection,open up small clip and tighten onto hose,do not over tighten,then the large clips,top up radiator with a water anti freeze mixture,replace ducting.Start engine and run for 5 minutes,check for leaks around hose connections.Stop engine leave to cool down,then check and top up radiator if required.Job done
Regards gasman.