Here you go

Sorry for bringing this old topic back... but,

did somebody already see a stock water pump housing that wasn't drilled for the bypass? I'm having some weird temperature spikes at idle when running a thermostat in my stock 383 HP. Without a thermostat everything is fine, besides running a bit too cold. After reading this thread I'm sure that the missing bypass is the reason for this, but I'm curios why the stock housing doesn't have a bypass at all. Every picture of a #2780987 housing I found has the bypass drilled.

The heater circuit will also act as a bypass, provided there isn’t a closed heater control valve being used, and the core isn’t plugged.

You could always drill a hole in the housing too.

Thanks. Yes, drilling the hole will be on the agenda. I was just surprised to find a housing without a bypass. After trying to cure the symptoms with different water pumps and thermostats for years I was running out of ideas why the engine would idle for hours at 140 F without a t-stat but would jump like crazy between 180 and 230 in seconds when operated with a t-stat.

quality control wasn't a "hot" topic back in those years. [i couldn't resist ! ]

Look at the BB pump housing, they bypass internally when the thermostat is closed