70 c10 overflow bubbling

[mhoneycutt85]

Hey everyone,

As stated above, my c-10 is overheating and seems to have trouble releasing pressure. I have an overflow tank on the truck, but after taking the truck down the road for a while and upon parking I hear bubbling and the radiator is spewing into the overflow tank. The overflow tank I have is one with the snap top cap so it has enough pressure after a minute or so to actually pop the top. My first thought was the thermostat, but I replaced that and while the truck is running I can see the water moving in the radiator. My temp gauge is very intermittent and sometimes will peg itself and then brings itself back to a normal reading. No water in the oil so far and no white smoke. The truck runs strong and doesn't want to cut off once it "reads" hot. I am really concerned about this overflow issue as I can feel an enormous amount of pressure on the top radiator hose. Any suggestions or things I should check before taking on the worst case scenario projects?