Today on a very hot day with AC running I got stuck in traffic and my coolant temp climbed up to about 105C, but I didn't hear the main cooling fan (actually I've never heard it). At what temp should it stop free-wheeling and start spinning fast? My aux fan is working, but I don't know about the main fan.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL