The heater core valve is missing. The circulation of fluid through the heater core is constant, which improves the overall cooling of the engine.
1. Check the tightness of the drain plug or plugs.
2. Remove the plugs from the two bleed holes.
3. Fill in a cooling liquid through a mouth of a broad tank.
4. Screw the plugs into the bleed holes as soon as the liquid begins to flow out of them in a continuous stream.
5. Start the engine (bring the engine speed to 2500 rpm).
6. Within about 4 minutes, add fluid to the reservoir, and the fluid level should be as close as possible to the upper edge of the reservoir neck.
7. Close the cap of the expansion tank.