Pully Question

Dr. Claw said:

The waterpump just went out on my 96 S600 with 105k miles. Not bad. Fortunately for me I was a 1/2 block from the house. I'm looking up parts and I need to replace everything and have found all but the tensioner pully. My questions are:

1) Are the pullys for the idler and tensioner the same?

2) When replacing the thermostat, do I have to replace the housing too?

3) Do you reccommend replacing the belt tensioner mechanism too?

Thank you for your input.

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Idler and tensioner pulley may be the same size but the bolt and bearing set may be different. On your V12 the thermostat is part of the housing, o rings should be included with the new one.
The belt tensioners are tough, the spring last a long time. Sometimes however the pulley is not included, when you slacken the belt to proceed with repair use good judgement of the condition of the spring. I don't doubt however it is in perfect working order. Did an alternator on a S420 with 246k and the tensioner was original and still very very strong. Good luck!