Originally Posted by
Swimholm
Why would you want to drill out the bolt with the pump on? Just finish taking the pump off. One time i had some good luck with a pipe wrench on a bolt i broke the head off. Either way it would be easier with the pump off.
The bolts for the thermostat housing thread into the pump, OP was asking if they should try without removing the pump, didn't sound like they were replacing the pump.