Hi
My 2004 Durango is loosing anti-freeze.
V8 4.7 liters
No white smoke from exhaust pipe.
No leaking hose or under engine.
Anti-freeze check -37 on tester
Original rad cap? Could it be the cap
That’s loosing pressure?
Thermostats opens fine and see circulation of anti-freeze
When engine is hot and thermostat opens
I add anti-freeze to side container every second day

 

Yes it could be the cap. Have you check the cooling system with pressure tester and if you have for how long? I have seen water pumps leak from the weep hole, only when the engine was running. You could also remove the spark plugs and crank the engine over and watch for any coolant or water coming from the cylinders.