Bi-Metallic Vacuum Switching Valve (BVSV)

Drain coolant from radiator into a suitable container. Remove BVSV from coolant outlet. Cool BVSV to less than 95°F (35°). Check that air flows from pipe A to pipe C. See Fig 1.

Fig 1: Testing BVSV Valve Do not submerge valve above threads.
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Heat BVSV to more than 129°F (54°C). Check that air flows from pipe A to pipe B. Apply a liquid sealer to threads of BVSV and reinstall. Fill radiator with coolant. If a problem is found, replace BVSV.