Damn that sucks. Wonder what the hell the issue is.
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Big SWAG that is usually the opposite of over-heating, but was the hose that connects to the overflow reservoir replaced? There's a reducer inside there that is vital to the operation of the cooling system - sometimes replacements don't have that. However, the symptoms of that are usually slow to reach operating temp and running way cool. Who knows at this point?
Coolant is filled to the full line.
....Tried it again and I was using the wrong adaptor I guess. But found a slow leak on the Y (split hose to) to the water pump. So i guess that's next