Cooling system locking cap (Opel Vectra B)

In the high-pressure circuit, the cooling system shut-off cap on the expansion tank plays an important role:

• The sealing surface of the screwed cap is pressed tightly against the edge of the expansion tank opening. The pressure cannot decrease
• If the pressure in the cooling system exceeds 1.2-1.50 bar during heating, the high-pressure valve opens. A little steam can escape through it in order to balance the pressure.
• When cooling, the liquid is compressed again. As a result, a certain underpressure occurs in the cooling system. To equalize this underpressure, there is a second valve in the cover, through which atmospheric air can enter the system.

Checking the high pressure valve

Those who do not want to waste time on checking, in a suspicious case simply change the relatively inexpensive cap. In the workshop, the locking cap is checked with a pressure gauge:

• Increase the pressure using a pump.
• Between 1.2-1.50 bar the valve should open.

Checking the low pressure valve with improvised means

The correct operation of the pressure relief valve can only be checked indirectly:

• After removing the shut-off cap, firmly clamp the thick water hose.
• Put the lid on and screw it on.
• Release the hose.
• If the squeezed hose becomes round again, the valve is working properly.
• If the coolant hoses are flat in the morning before the engine is first started, the low pressure valve is probably faulty.