Many mechanics are unaware of the causes of this condition. I have tried to compile all of the info that I have found surrounding this issue here. Most of this content was collected from on-line accounts.
96 -2000 Caravan / Voyager
Serpentine belt being frequently thrown off of the pulleys while driving in any amount of snow or rain.
If any of the components along the path of this belt are having issues, this can cause problems with the belt. We are not concerned here with belt failure due to normal or predictable component wear. Belts and components should be checked regularly as part of routine maintenance. This description deals with frequent belt failure due to pulley alignment not directly associated with obvious mechanical failure.
This serpentine belt system relies on near perfect alignment between all the pulleys along the belt. ANY changes in the alignment can cause the belt to slip off of the tensioner as it does not have raised edges (side walls).
It would appear from the accounts that marginal bearing wear or other foreseeable minor tolerance changes (component replacement without shimming for perfect alignment, pulley surface wear, bearing surface wear, or mounting slippage of any of the 6 component pulley systems along the belt path) can contribute to this condition.
A qualified repair shop should have a pulley alignment checker which uses a laser beam to check component pulley alignment. However, it is obvious from accounts that not all shops are aware of the delicacy of this alignment and may recommend expensive ?shot in the dark? replacements of the individual components. Component shimming may be required.
It is my understanding that there were two Chrysler TSBs (Technical Service Bulletins) on this issue. Neither one directly addresses alignment accuracy and Chrysler may be assuming that all of its mechanics are up to date on this aspect.
TSB 07-09-99 (AllData has an article about it). Pulley guard/pulley shield" (Chrysler Part # 05003480AA). It will also need a longer screw to hold both (# 04556218). essentially this is a washer that keeps the belt from slipping off.
!!! After any of these repairs, ask the dealer to pour a small amount of water onto the belt (while running) to see if the belt will slip off. As far as I am concerned, no amount of water should cause a belt to slip out of position!
Aftermarket fixes - Gates/Goodyear
This solution has had overwhelmingly positive reviews, but be warned, the parts are $100 -$160 and you are now committed to buying specific, non-standard belts for this car from then on. The kits do come with a warning sticker to this effect. It?s a belt and pulley kit that replaces all of the smooth pulleys with grooved pulleys, and the belt is ribbed on both sides.
Gates Fix kit info:
1996-2000 3.0L V6 = 38342K
1996-2000 3.3L/3.8L V6 = 38379K.
1996-2000 3.0L V6 engine = 49204K
1996-2000 3.3/3.8 V6 engine = 49215K
Should be available at NAPA, Rock Auto, Amazon and CarQuest.
Aftermarket fixes - Dorman/Advance
Dorman disk covers from Advance Auto generic pulley shields This fix may also require some rework or modification of the tensioner pulley bolt and shimming arrangement.
Aftermarket fixes - GM part retrofit
Some raised edge GM pulleys can be substituted in for the Chrysler original.GM Part 14102645 - Tensioner assembly off an 87-93 S10 with the 2.8L V6
Some aftermarket GM replacement parts don't have the raised edges to keep the belt on. Check before you buy. This fix may also require some rework or modification of the tensioner pulley bolt and shimming arrangement.
Aftermarket fixes - Rockauto /Four Seasons generic pulley retrofit
Four Seasons part #s 45970 and 45887 (plastic pulley with flange made in Korea). This fix may also require some rework or modification of the tensioner pulley bolt and shimming arrangement.