Radiator pressure and bubbling

[Skynite]

Hi guys need a big help...
I own a isuzu 4jg2 intercooler turbo bighorn.
Recently had an issue of water reducing at Rad when run for short distances and when I check next day morning, water is reduced a bit (a bit less than half a litter). And at long run, it pulls water from then subtank. And the level in rad is ok bt subtank reduced. So I got it chkd, Rad was bubbling on start without the CAP. So assumed gasket was the issue.
Replaced gasket, put new valves , head was check for cracks,
Engine was fixed up but the problem was still not solved.
Tightend head bolts again. Didn't solve
Removed the gasket again and put another, stil not solved
Doesn't seem to have a problem in the block. Looked good. Previous owner had done a rebuild with new sleeves on it. But yet the Rad is bubbling and water pours out.
But engine doesn't overheat, it never did even before at first attempt to remove the engine.
Temp gauge works properly.
No oil it the coolent or no white smoke, no white slug on oil cap. No water on engine oil. Waterpump has no sound or play,
Only problem is that it bubbles and reduces a water abit, and when I open the RAD cap next morning it releases pressure.
I flushed the RAD once but it's abit dirty inside yet.
What could be the reason? Would a RAD block create such issue? I didn't do anything with the Heatercore as to get the air out of the RAD system. What could this probably be?

[geeves]

that really sounds like a cracked head

[Davidf]

Did you ever solve your issue. I have the same issue put a brand new head and head studs still happens.

[geeves]

A garage will be able to test the system to see whats going on. 2 things can cause bubbling.
If you are lucky its still bleeding air out of the system and will stop soon. Make sure the heater is on full and idle the engine with the occasional rev untill the engine is up to temperature and the heater is hot.
If not lucky the combustion is still leaking. This could be a badly seated gasket or not torqued up correctly. Did you use new studs? It could be the head is faulty. Was it new? It could be a crack in the bore which will really ruin your day

[Davidf]

It was a new head and new head studs.

[geeves]

Did you torque it as per the manual?

[Davidf]

Yes I did. I think I'm gonna pull it down and check the block make sure it's true and flat