My E 450 has a lot of items revolving in the motor, most of which get plenty of lubrication. Three things come to mind that are not lubricated. Water pump bearing, altenator bearing, and the idler bearing on the belt tensioner. On my 12 year motor, with 40 k should I be concerned about these items, and maybe doing some preventive maintenance? Thanks for your input. stan

 

No, unless you just want to replace still-working parts that have an indefinite service life with a new part that also has an indefinite service life.

 

At 40K miles that motor is barely broken in which includes all the components you mention. I'm driving an '00 E250 with original motor and most of its original parts as well. Alternator was replaced 30K miles ago but that's about all.

Belt tensioner will go at least 100K so maybe once there consider changing it along with the belt. In fact I'd change the serpentine belt at 50-60K miles---its a $40 swap at most, assuming you buy good stuff.

HTH