If that's the common factor, it's water making the serpentine belt slip. You can prove that by dribbling water on the belt while the engine is running. The belt could be worn but more likely the spring-loaded tensioner pulley isn't holding enough tension on it. Also look for any pulleys out of alignment, typically due to a failing bearing that lets that pulley tip.

Answered by caradiodoc (expert)
17,660 answers provided