Table of contents: Checking the safety valve ↓ Checking the vacuum valve ↓
In a circuit with excess pressure, the expansion tank cap of the cooling system plays an important role.
The sealing surface with the cap screwed on must be pressed tightly against the edge of the expansion tank opening. No steam under pressure should pass through.
If the pressure in the cooling system exceeds 1.2-1.5 bar during heating, the safety valve opens. In this case, some of the steam is released to equalize the pressure.
When cooling, the coolant decreases in volume again and a vacuum occurs in the cooling system. To equalize the pressure, there is a second valve in the cap. It opens at a pressure of 0.06-0.1 bar and air from outside can enter the expansion tank.
Checking the safety valve
Create pressure using a pump.
The valve should open at a pressure of 1.2-1.5 bar.
Checking the vacuum valve
The only way to ensure that the vacuum valve is working properly is to perform a test.
With the expansion tank cap removed, squeeze the thick coolant hose. Replace the cap and tighten tightly.
Release the hose.
If the compressed hose straightens out again, the valve may be faulty. If the coolant hoses are compressed in the morning before starting the engine, the vacuum valve is probably not working.