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Robert, UK Qualified Car Technician
Category: Mercedes
Satisfied Customers: 5307
Experience:  Fully qualified / self employed garage technician in the UK
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The fan belt on my Bclass has snapped 7-8times in the last

Customer Question

Hi the fan belt on my Bclass has snapped 7-8times in the last year. Why is this happening?
Assistant: What shape is the fan belt in? Do you know if it needs to be replaced, or just adjusted?
Customer: Fan belt snaps and falls off. I have had the tensioner pulley replaced 2 years ago.
Assistant: What is the model/year of your Mercedes?
Customer: bclass 2.0 cdi cvt 2008
Assistant: Are you fixing your vehicle yourself? What have you tried so far?
Customer: Garage replaces the fan belt
Assistant: Anything else you want the Mechanic to know before I connect you?
Customer: No
Submitted: 7 months ago.
Category: Mercedes
Expert:  Robert replied 7 months ago.


Could be several reasons for that.. the tensioner is known issue .but seeing as you have replaced it cold maybe rule that out.. worth noting how the belt is actually failing might give a clue as to whats going on..if it frayed at the edges or been rubbing then that would mean one of the pulleys that belt is running over is out of alignment or has slight play causing the belt to walk off the pulleys...obsevering on the engine for any rub marks from the belt might give a clue too.. you can get laser alignment tools for belts/pulley alignment but they are expensive.if your garage has one then try it and see.... One other thing springs to mind is the Alternator clutch pulley might be failing - they could maybe test that by taking the serpentine belt off - Carefully stick a screw driver into the cooling fan on the body of the alternator to hold the internals still - Rotate the pulley by hand - it should be freewheel in one direction and lock up in the other..if its not doing that then your alternator clutch pulley is bad..