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1990 plymouth voyager van

serpentine belt falls off when it rains

Something’s really out of alignment, or the tensioner is done.

Why it only happens in the rain…dunno…

This is a common problem with these cars/most of them. Do you have the splash guard next to the belt area or has it fallen off? Gates sells a belt and tensioner kit that is supposed to fix this problem. You can look on allpar or other Chrysler sites/forums.

It is a common problem with those vans. If you drive in heavy rain, or through a deep puddle, water splashes up on the serpentine belt. And basically what happens is water gets underneath the belt on one of the pulleys (one of the smooth ones that is driven by the back of the belt) and it hydroplanes off of the pulley, just like driving a car to fast in the rain. There are several different solutions that people have come up with over the years to fix this. First, there should be a splash guard to protect the belts. Its just a plastic cover that starts at the bumper and keeps things covered. The second is to replace the tensioner, even if it seems fine. The springs can get lax as time goes by and the tension on the belt is lower, and it makes the problem worse. Third is to take some course sandpaper and clean up the surfaces of the pulleys that run on the back of the belt (idler, tensioner, possibly water pump depending on which engine you have) If it still has problems, there is a kit which replaces the offending smooth pulleys with ones with grooves, and a new serpentine belt, that has grooves on both sides. Replacing the tensioner though is what cured it on my landloards van. your mileage may vary.