Problem:
Truck is overheating. The upper radiator hose stays cold even when the temp gauge shows hot/overheating. Coolant in the radiator rises to the top but does not appear to circulate.
What I’ve tested:
Used a block tester (head gasket test kit) → fluid did NOT change color (no combustion gases detected)
Coolant level is full
Watched radiator with cap off from cold start → coolant rises but no noticeable flow
Other symptoms:
Blue smoke from exhaust (noticeable at [startup / idle / acceleration])
No constant bubbling in radiator
Heater blows [hot / cold / inconsistent]
Question:
Does this point more toward a stuck thermostat or circulation issue (water pump or air pocket), or could it still be a head gasket or cracked head even with a negative block test? Also, could the blue smoke be related or is that likely a separate issue (valve seals, rings, or intake gasket on the 5.9)?