gurgling disco vu

have a 95 v8, 3.9 ltr disco, which has the common gurgling from the heater matrix, proving very difficult to solve this , however I noticed yesterday after a 70 mile drive , that their was next to no pressure build up when I released the expansion tank cap ? not losing any water, but seem to be running a bit warmer than usual .
could the two symptoms be connected ? and any idea what of ? The engine was rebuilt only 2k ago