I have a 2001 Discovery II. I just ad the top end rebuilt and replaced the radiator, thermostat, and water pump.

The cooling system will work correctly for a few days until it builds up air pressure within the system. I bleed the air out through the valve near top of fan and it will run fine for a few more days before I have to do the process all over again.

Temperature stays completely normal for 50-100 miles before climbing toward red zone. If I catch it before it gets too close the red zone, no coolant is lost in the process. Of course if I can't pull over quick enough and it gets too close to the red zone, coolant is ejected out the reserve tank.

Any idea?

No coolant is present in the oil and no coolant is coming out the tail pipe. No coolant is leaking from the heads either.

Thanks in advance!!