Bad thermostat. Fan clutch is operating normally. It should only bring the fan to an immediate stop when it's engaged, which would be when it's hot. I don't think your coolant temperature is getting hot enough to engage the fan clutch.

It won't do any significant harm to run it that way for a few weeks, though it will affect the operating characteristics of the heater and may cost you a few mpg until you get it fixed.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.