318 overheating
This is an imortant question that no one asked yet.
Does it ever push water out the overflow?
If not, then it's not a head gasket.
Thats an excellent observation. Mine doesn't.
I have changed my water pump (old one was perfect) ALL hoses and clamps.
I get in, drive 3 miles, and it is on H+
I cool off the rad cap, lift the release lever, cool it with water again and with a rag I slowly remove it with an accompanying burst of steam water and whistling plus overflow tank steam emissions and loud noises...HOT ENOUGH FOR YOU?
I went to a Stant after trying 3 AutoZone 195 deg. stats and a "Fail Safe" AutoZone stat that froze open immediately and never closed again...TRASH
For years I would drive off in the morning and 3 miles down the highway it would be all the way to H and then quickly go down to normal...EVERY day, without fail for 12 years. Stupid me, I decided to change the thermostat.... So I changed the stat and have had nothing but trouble every day...every damn day since.
Every day I start up drive off, go 3 miles, remove a fiercely hot cap, steam and noise everywhere...pour a 1/2 gallon of water in, get in the truck, and its OK, on NORMAL and drive to the grocery where I top off the radiator with water. The rest of the day it is fine. Next morning, ity all happens again...exactly the same, every time.