Date registered: Feb 2008
Vehicle: 2004 W220 (S430) ; 2001 R129 (SL500) Sport
Location: Alabama Gulf Coast--formerly Charlottesville, VA
Mentioned: 0 Post(s)
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Check the viscous coupling on the cooling fan. As I remember from my W108 (sold 20 years ago, sadly), if that coupling packs it in, the fan will slow to almost stop when it idles. It's the opposite of the coupling locking up so it spins at water pump speed all the time. It sounds idiotic to ask, but did you put the cooling fan back on when you reinstalled everything?
"Don't pick a fight with an old man. If he is too old to fight, he'll just kill you."--John Steinbeck