My 76 242 dl (b21f) temp guage used to read on the high side, showing that it was running hot. it had a new rad, water pump and t-stat... I also noticed that the temp guage would get even hotter with electrical accesories on (head lights, fan, rear de-frost...etc) Stumped by how the engine temp was related to electricity use, I re-grounded the engine to the chassis, and a new ground from the battery to the chassis. this fixed the "overheating", in my case a bad ground caused the temp guage to read high.

but... if u have a leakey head gasket...fix it before you have a larger problem...bottom end damage from overheating

dave
82 242 glt (b23e-canadian) 420 Km
76 242 dl (b21f) 156 Km