I've often seen the six little holes that are added to the 261 referred to as steam holes for whatever reason. Not sure what the difference is other than one might be more for coolant flow and the other designed more to release steam pressure due to the siamesed cylinder cooling jacket on the 261 block that differs from a 235 block.
The 261 was also designed for a bypass thermostat. Some folks will argue that is only necessary because the larger trucks might have engine strain before proper warm up. As much as I agree, I think this is probably secondary. Others (like me) will argue that the primary reason GM engineers added the bypass thermostat had more to do with the siamesed cooling jacket in the 261 block requiring coolant flow at all times. I think the steam holes and the bypass thermostat were an integrated design by the GM engineers for the 261.
Patrick's had just received the gasket set from Best and I picked it up from him the day it arrived. The package was sealed. The error was on the part of Best, not Patrick.
Matt
Last edited by Maybellene; 12/19/2016 4:58 PM.
