I'm trying to diagnose vehicle 750 miles away in order to decide on purchase. Is there any reason to doubt that the reason the cerpentine jumped off is due to cap screw comming out of fan and pulley assembly allowing pulley to wobble. If it resembles my 240D, the water pump is the shaft the pulley and fan are mounted to. Could the water pump bearing be so bad it could throw the belt? It was to have failed 2 miles from home and no overheating limping home. Coolent level is supposed to be within range.

it is much more likely to be the belt tensioner arm and related shocks / springs. The bearings wear and the belt begins to slide off the front.

It doesn't make much sense for the car to even be running with the fan flopping around like that. - such as would be required to disengage the belt from the pulley

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Be careful, 2 miles could have been 20 miles & a cooked motor. Water pump bearings could get that bad to cause belt problems. I would suspect a problem over some time.
Do not make a decision to buy unless you have had the motor looked at by some one who knows a bit about these motors & is sure there is no other associated problems eg head warp or gasket blown.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving