MB does not say when to change them. The official line is to inspect them and replace when they start to crack. If you look at where the tensoner pushes against the back of the belt exposing the rids, you will see cracks if the belt is tired. If you don't see any cracks, its fine.

I know several that have lasted quite awhile, my friends 97 S320 still has the original. But it has small cracks starting and is due soon. My other friend changed his at about 145k on his E300D.


You do not want to have one break though, not only will you be stranded. But it could do a bunch of damage to other things. My friend had the serp belt fail on his 735IL awhile ago, original belt car was 8 years old at the time. Belt failed on the highway and ripped the upper radiator hose off the neck, snapping the neck of course. So insted of just replacing a $40 belt he had to replace a $500 radiator, plus a cooling hose, plus coolant, and the $40 belt.

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2006 CL500
1969 280SE
2023 Ram 1500
2026 Genesis GV70
2007 Tiara 3200