international 175c pressurized coolant issues again

Hey Mr Delmer thanks for ur reply, well im new to this forum an been trying to figure out how this site works cause id been having issues replying ur mess. but with my 466b I have like before experienced these air bubbles in pure water before my inframe job, an after the inframe I put antifreeze in it, still pushs water out under press., I don't have a therm. in it due to I threw the old one away before I did the inframe an noticed the pressure, though it was trying to overheat due to it was sticking, so I tossed it,, well ive worked at Cat for yrs then layed off, im very aware of the opperations of the therm. and how important they are, just like why its not good to run water in tractor radiators an not coolant, but were all guilty as the next guy that does it, lots of people in summer time will use regular water that's at there easiest reach like from a lake,creek,stream or even mudd puddle, heck our rad. is low an water is water right, I though so too till when cat sent me to school I learned that how pure water is hard on cooling systems due to the alkalinity,acids,phs are all unbalanced an over time will develop electrlises ,(means the break down of the internal parts of the cooling systems as in pitting of cylinder liners from the inside out an eats up all aluminum parts too , not to mention water dosent have lubrication in it.) but it dosent happen over nite an takes time to do we never think about it today an worry bout it down the road. but yes I had coolant in it after the rebuild an complete head reapair , new injector tubes,valves,guides,seats. an yes ive took temp. readings at top of rad. an bottom, there is a 15 to 20 degree differ in it so therefore it has good flow, water when look inside of rad. while running it seems to have great water movement. plus don't think its the pump due to it builds press while at cool temp. but the warmer it gets the more it builds press. im not sure were the temp sensor was, think it was on therm. housing, but between the housing an exhaust manifold theres a plug I removed an installed a new mech. temp. gauge in. it seems to read higher than my hand held temp gun, ive used differ guns an there very close to each other but comared to the mech. gauge theres nearly 20 degrees differ, even exchanged mech. gauge few times to see if it was off,,,,on therm housing theres a plug there but ive tied my hand help primer pump tester there to read pressure. if I pump above 15 itll push the water outta the rad. vent pop off valve . back when I ran the hose from pop off into the bucket it was pushing bubble an coolant out into bucket , when its starts the water issues itll blow a lil then stop then blow lil an stops, I watched this over nearly an hr till I loved over an noticed my bucket was gargleing an steaming like crazy, I took a temp reading an it was round 200 but that's now boiling over nor overheating, I shut it down to cool off then pulled head off an took back to shop to havem look over, they got back with me an said hadn't found nuttin they pressure checked all tubes an checked for cracks, even leftem my gasket,,,, they found nuthin. so im bout to reinstall the head again an im gona recheck the liner projection (the height of the liners from the deck of the block) but normaly when one of them are outta specs ya blow lotta head gaskets. dout this is my issue. don't know were else to look cause not lotta things in factor here, head, jecture tubes,gasket,liners,therm,waterpump. don't know bout crack in head an opens up when temp rises, cause the press developes in water way before operating temp.