Hello guys! I have a 58JCW and last night I had a drive, I saw the engine temp rising so quickly so I have a check at the coolant tank and the coolant cap have pop out (I think I didnt screw it tight enough last time when I check the coolant and oil) . Then I turn off the car let it cool down abit then I add some water back to the coolant tank. After adding water I had a blast, and the car is fine, no more overheating but the temperture runs between 98-107C rapidly so I assume there are some air in the system, after I back home I left the car till today, the coolant level has drop to nothing in the coolant tank so I bleed the system again.

I first unscrew the bleed screw and pull water into the coolant tank, no water coming out from the screw and the coolant level wasnt droping. Then I turn on the car with full heater on with max fan, no heat coming out from idle, heat only comes when I rev up the car. I run the car till 105C and check the bleew screw again no air sound and no coolant coming out water level not dropping also. If there are no water and air coming out from the bleeding screw, is that a thermostat fail?