1997 b3500 extended van. 5.9v8 ---

ive had this no pressure in my upper radiator hose issue for a while now. strange thing is a few days ago i noticed it was building pressure and keeping temps cooler while driving, its been 95-100 in the midwest here so the heat really affects my operating temps. so when there is pressure in the radiator hose my temps read normal operating temp and it does not jump above the 1/3rd marking. which is what it should be doing all the time. additionally when the cooling system isnt building pressure in the top radiator hose the temp guage will shoot up to half way and on hotter days it will jump further close to the 2/3rds ( above middle) position. operating almost twice as hot with no pressure. . just changed thermostat and did a full coolant flush. no visible leaks, new hoses. what else would cause this? these days are getting hot and its not normal to not have pressure in that hose. i know coolant under pressure increases the boiling point. could my water pump be bad? and if it was my heater core leaking, wouldnt it drain out of the AC box? what about air bubbles? how would i burp this thing and make sure there are no air bubbles? thanks for reading. i need help asap.

 

Did you replace the radiator cap?

 

no it seems to be fine tho.

 

Actually ended up being the radiator cap. seals were busted. replaced it now i get pressure building in hose. running at cool temps and every thing seems fine. Although when im going 80 with aload in the bed it gets close to half mark. normally it stays under the 1/3rd mark at " normal operating temp. should cleaning the debris off the radiator fins help this stay cooler?

 

Sure won't hurt.