Checking pressure relief valve in cap:

WARNING: This page is about a different car, the 2002 BMW Z3 and 2001 BMW Z3. However, it is still accessible from the selected car via links, so may be relevant.

Detach rubber (1) from hand pump.

Fig 1: Detaching Rubber From Hand Pump

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Attach special tool 17 0 007 / 17 0 008.

Screw cap (1) onto special tool.

Fig 2: Installing Cap Onto Special Tool

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Build up pressure with special tool (hand pump) 17 0 002; observe pressure gauge to ascertain when opening pressure is achieved.

Compare opening pressure of pressure relief valve. Refer to 17 11 RADIATOR AND MOUNTING PARTS M52TU / M54 or 17 11 RADIATOR AND MOUNTING PARTS E36 / M50 / M52 / M54 .