ok so yesterday i changed thermostat and upper radiator hose. the way i bled the air was just left the cap off and let it bubble. i figured it was good it bubbled then level dropped so i capped it off and let it run. i drove it for about a half hour and came home it didnt leak. so today i started it up and turned it off a couple times havent driven it after a little while of it running i turned it off never let it get warm i noticed a steady stream out of the resevior capso i pulled the capp off and it spewed of course with the cap off i let it get to running temp till i saw the thermostat and the level dropped and i capped it. and it hasnt leaked. what would cause this?
the truck never overheats

 

You have another thread in the V8 section regarding your new truck and cooling issues. Keep everything in one thread to keep the confusion down. It sounds like you have a block in the system, air pocket or exhaust gasses.