Warning! Do not remove the expansion tank cap when the engine is hot, as you may be burned by hot fluid vapors.
The coolant level in the expansion tank changes depending on the temperature. When the engine is cold, the coolant level should be at the mark located on the side of the expansion tank. After the engine warms up, the coolant level should rise above the mark.
Wait until the engine cools down and slowly unscrew the cap from the expansion tank.
Pour the water and antifreeze mixture into the expansion tank up to the mark. Screw the cap onto the expansion tank.
Original material on the website (MERCEDESMAN.ru)