1984 s-10 blazer 4x4 overheating issues
 

my truck has recently started overheating first it was only running hotter than normal so i changed my thermostat and did a coolant flush and fill yesterday the truck overheated to the red so i pulled into a lot and shut it off i was thinking maybe the new thermo was junk so i tried to restart it and it didnt want to start because it truly was overheated.my radiator cap has a red lever on it i was going to crack the cap to try and cool it down quicker but when i pulled up on the lever on my cap all this hot coolant rushed to my resivor and it was like boiling so i let fill up then i got in the truck and it started right up and was just a little above normal opperating temp any help or comments would be greatly appreciated thank you