The electric fans are only really important if you are running the AC, other then that they almost never come on. On my SDL at least they don't kick on until 105C.

I'd say the viscus fan clutch is week, or your radiator is clogged. Overheating under heavy load is a classic radiator problem.

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2006 CL500
2009 C300 4matic
1969 280SE
2023 Ram 1500
2007 Tiara 3200