Checking pressure relief valve in sealing cap
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NOTE:
While driving the vehicle at high outside temperatures, depending on the design, the pressure relief valve in the sealing cap can open slightly and air, together with dissolved coolant, can escape. This coolant vapor condenses on the surface of the expansion tank and leaves traces of coolant when the vehicle has cooled down. These coolant traces do not indicate whether the cap is defective or not. When the vehicle has been parked up for an extended period of time, the residual escaping coolant can cause the pressure relief valve in the sealing cap to stick; therefore check the sealing cap again 2 to 3 times.
Replace the sealing cap only after you have checked three times and there is an incorrect opening pressure .
Screw sealing cap (1) onto special tool 17 0 114 .
Build up pressure with special tool (hand pump) 17 0 101 ; observe pressure gauge to ascertain when opening pressure is achieved.
Compare OPENING PRESSURE of pressure relief valve.