block heater replacement

[marcocor]

99 k2500 sub block heater packed it in do I have to drop all the coolant or can I drain just the block ?

[FloridaHorseman]

Draining the block will put you close to draining 2/3 or more of the entire system. IMO, might be a good opportunity to do a complete system flush and recharge it with fresh coolant for the winter. ~FH