I have a 1985 deville 4100 engine
My problem is the pulley on the water pump keeps coming loose. The first time this happend was last summer I put new bolts in and all seemed ok until this morining in the way to work the pulley came completely off. I checked all other pulleys to make sure nothing was locking up up Any Idea what would cause this?

 

Hey Lexus: Do you have lock washers on the bolts?? Star washers would works also. There must be more than normal vibration in the pump shaft for it to come loose on you. Maybe the water pump is next?? Take a good look at the fan when it is running and see if it has a wobble.

 

This engine had a habit of loosing the flange that holds the pulley to the water pump. In other words, the plate pressed on the water pump shaft comes off! So, take the pulley all the way off and ck the flange it bolts to. If loose, its water pump R/R time! Also usually whenthe pulleycomes loose it damages the holes the bolts pass thru, which will cause the bolts to loosen again! If you are lucky, simply replace the pulley and the idea of star washers is a good one.