The expansion tank is made of transparent material so that the brake fluid level can be checked from the outside at any time. It is recommended to regularly glance at the expansion tank.
The liquid level should lie, with the lid closed, not higher than the maximum mark and not lower than the minimum.
Fill only specification brake fluid SAE J 1703, DOT Z.
Due to worn brake pads, the brake fluid level drops slightly. This is fine.
If the brake fluid level drops significantly in a short period of time, this is a sign of brake fluid loss.
The leak should be located immediately. As a rule, it is located on worn cuffs in wheel brake cylinders. For safety reasons, it should be checked by a specialist workshop.