Water pump bypass?

[john.thompson068]

Why would a Chevy (yeah I know, go to a Chevy website) have a bypass? I found this odd bit of information while researching thermostats. BME/Stewart modifies Robert Shaw thermostats to have three bypass holes because their water pumps for Chevy's no longer have the bypass.

 

[67 coronet]

i would figure it has to do with design differences.the chevy system is a sealed waterpump and dodge is a waterpump fitting into a housing.the chevy will probably build too much presure if totaly sealed.