Pic. 136. Pressure testing of the cooling system and expansion tank caps
A special pump is used to check the plug. A cork is screwed on it (pic. 136, bottom), then pump until the valve opens under pressure. The pressure at which the valve opens is 1.4–1.5 bar if the plug is still new. A used cork must withstand a pressure of 1.3 to 1.4 bar. Otherwise, the plug should be replaced.
Using the same pump, you can check the tightness of the cooling system. It is screwed onto the filler neck through a special adapter (see fig. 136). After that, it is necessary to create a pressure of 1 bar, which, when checked by a pressure gauge, must be held for at least 5 minutes. If this does not happen, there are leaks in the cooling system that are easier to detect when the system is pressurized.