merc sprinter 311cdi; randomly, starter wont operate on key. can turn key dozens, hundreds of times and starter wont operate. Suddenly, starter whirs and its ok till the next time, days or weeks later. Apparently completely random

smileyken, April 2009

first of all if the starter "whirrs" when the key is turned its a new starter, secondly, if you turn the key and the starter does nothing thats a different kettle of fish soup my friend, transponder temic, or starter relay. Call me if you have any further problems. All details on my website

williamsdiesels.com, April 2009

Sounds like you have a classic case of a sticky solonoid which activates the plunger to start your engine and its located at the top of your starter motor if this is not working first time the motor will just spin without engaging the main flywheel,
Its not big problem can be solved by taking off starter motor and cleaning you can test the starter motor just by having an old charged up battery, if cleaned and working properly you should see the plunger shooting in and out dont worry it wont come right out as its enclosed usually its about 3 bolts to undo and take off the underside of the engine.
But beware always disconnect the battery as you can easily cross the terminals and make connection with the feed

Ian Mechanic, April 2009