Still the same iv tried everything even had the head of checked hg and fine and had head skimmed an pressure tested at 1 point had oil in water so changed oil cooler but still pressure also have put a coolent flush through doin my head in now haven't a clue what it is

 

I have exactly the same problem with mine at the moment as to the point it builds up that much pressure it pisses out of the header cap...... Heater works spot on and doesn't get no more hot than normal when driving I'm whipping the head off as I want it doing as piece of mind .....

 

Iv had my head of and checked etc went for a drive last nyt never got hot but pipes where rock hard turned engine of and herd bubbles pipes stayed hard checked again around 5-10 mins l8r and they went soft

 

Wen u next take it out wen u come back put the heater on flat out hot for 2 mins on tick over see what it does then

 

I do that anyway it did creap up bout half way on gauge turned it off but left ignition on and it went up to 3/4 on gauge