I have a 2001 with 185,000 miles. I have replaced a number of items like plugs, wires, hoses, waterpump, belt, etc. as PM items. I'm looking for suggestions as to when I should replace the alternator as opposed to letting it die and putting me on the side of the road 50 miles from home.

 

theres isnt a set mileage or time frame they will last. they will last until a bearing fails, the brushes wear out, or the regulator fails. id say 5 to 10 years is a reasonable time. sometimes new ones will fail out of the box or shortly after or they could last 20 years. i would run it till you notice sounds coming from the ALT or lights don't seem as bright

 

A couple of things I've noticed over the years. If your lights flicker severely, Check the battery terminals. If they are clean and tight then the ALT is starting to go bad. If you hear a whinning sound when you start up in the morning Its usually a bad bearing in the ALT Check to make sure the belts are not too tight if not Change it.

 

you could always have it rebuilt by a trusted rebuilder. If he is good he will check all parts, replace worn parts and test it before you get it back in hand.