Overheating/fluctuations with vintage air.

[pound41]

I recently bought my son an s10 blazer. it ran hot but didnt spike. I noticed the radiator had been replaced and the top hose would bulge and seep. Ok its the thermostat. Replace the therm and top hose. Same thing runs hot. the temp comes down when you switch from ac to heat. It has to be the original water pump. Replace the water pump. It instantly spikes running hotter than it ever did. The overflow tank is now full. I slightly crack the radiator cap. The top radiator hose starts to make a reching sound and move. It was a lot of air. After that started it up and it runs cool. I saw a show on TV.Newly restored hot rod. Same problem. They had a special radiator cap that had one hose for liquid going in and another for air going out