BMW B58TU Reference Manual page 26

B58TU￿Engine
4.￿Cooling￿System
4.3.1.￿Cold-start￿phase
Point￿A￿in￿the￿heat￿management￿module￿circuit￿diagram￿designates￿the￿cold￿start￿with￿an￿engine￿that
has￿completely￿cooled￿down.
Cold-start￿phase,￿Bx8TU￿engine
In￿the￿cold-start￿phase,￿the￿coolant￿circulates￿exclusively￿via￿a￿bypass￿in￿the￿coolant￿pump.￿The￿rotary
valve￿in￿the￿heat￿management￿module￿closes￿the￿coolant￿lines￿so￿that￿the￿excess￿pressure￿that￿builds
up￿opens￿the￿pressure￿relief￿valve￿in￿the￿coolant￿pump￿(opening￿pressure￿2.1 bar)￿and￿the￿coolant￿is
recirculated￿in￿the￿coolant￿pump.
Because￿the￿coolant￿circuits￿through￿the￿exhaust￿turbocharger￿and￿the￿ventilation￿line￿of￿the￿cylinder
head￿cannot￿be￿closed,￿a￿low￿volumetric￿flow￿is￿returned￿to￿the￿coolant￿pump￿here.

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