cooling system pressure

my son has an 2002 silverado 1500hd.heater core blew out and he got truck hot.replaced heater core and had a little trouble getting air out of system.truck now runs fine at correct tempture about 190 degrees.problem is overnight all of the pressure does not bleed off.doesnt blow water out when you remove cap but will blow cap off if you dont hold it down.will this cause any problems?motor is the 6.0
thanks charles

I think you still have air in the system. Try raising the front end with a floor jack as it is idling.

thanks for the reply.put truck on ramps ran for about thirty minutes some air came out.drove acouple of miles will check in the morning for pressure on tank.if it had a leaking head gasket would it act like this?theres no oil in water or water in oil.thanks again charles

thanks for the reply.put truck on ramps ran for about thirty minutes some air came out.drove acouple of miles will check in the morning for pressure on tank.if it had a leaking head gasket would it act like this?theres no oil in water or water in oil.thanks again charles

YOU TAKE CAP OFF . START COLD ENGINE. RUN UNTIL ITS AT 190 DEG F . REV ENGINE TO 2KRPM SEVERAL TIMES . PUT CAP BACK ON.......... This is how you do the bleed on these. fill to the hot mark no more. It can happen !!!! pressure cap can get plugged up .. you may need new cap.

my son has an 2002 silverado 1500hd.heater core blew out and he got truck hot.replaced heater core and had a little trouble getting air out of system.truck now runs fine at correct tempture about 190 degrees.problem is overnight all of the pressure does not bleed off.doesnt blow water out when you remove cap but will blow cap off if you dont hold it down.will this cause any problems?motor is the 6.0
thanks charles

FORGOT TO MENTION do not use drinking water with the dexcool. do not mix dexcool with compatibles / universal coolants. GM dexcool is what is required WITH DISTILLED WATER ...............

ALWAYS use 50% antifreeze mix min. I use 65% has nothing to do with freeze its all about corrosion !