M103s have two different thermostat options, at least here in the US.

79°C and 87°C remember, that is when they begin to open

You do realize most domestic come with a 195°F or ~91°C... and that is when they begin to open.

Temps you are seeing are normal and fine. I would begin to be concerned if I was over 100°C into the 110°C area

Verify your aux fan switch works on the cyl head and motor on as well as the fan switch for the A/C system.

FWIW I installed the lower temp one in my 300SEL a while back as I became tired of the fan clutch locking and basically being locked in city traffic (really saps power from an already underpowered car). No issues with that now and no cooling problems after two summers.

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'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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