Engatwork, the 500 has a new fan clutch (BEHR). Today, we went out riding in the 500 just to see what it would do at 90 to 93 deg outside. It got up to about 95C or a little more when we were stoped in traffic but cooled back off to around 90C at 50+ mph.
Everyones comments have set my mind at ease.

Thanks everyone

PaulM

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84 500 SEL (307,xxx miles)