Hello,

My Mk2 was exactly the same.
New heater core - no change
New Thermostat - no change (but temp guage now steady)
Replaced hot / cold air vent flap material - no change

Rip out the Valve added for Mk2 heater recall - replace with copper plumbing pipe and it's now too hot.

I can see the coolant system "residue" that has blocked and seized it up.

Just need Air con regas for summer now