Esters are made by reacting alcohols with acids, which creates ester and water.  The reaction is reversible, so reacting water with ester creates alcohol and acid.  This is not a problem in most applications because the reverse reaction is very slow and difficult, and esters are designed to be used in high temperatures where there is little or no water.  Car engines, however, may have a wet environment due to water in the blow-by and condensation, especially when driven in short trips or stop-an