I hear about 180* drilled stat. I'm installing a 180 now but want to know what size hole to drill. What performance/hp gain this gives me? :?: I realize it might help circulation and air gap issues.

There'* so many threads on this, if you search you'll find a lot of good info.

Generally though, one or two 1/32" holes opposite each other is good. Many people have their preferences. You won't gain hp from the stat, but your engine will run cooler, helping it last longer, and allowing for better hp gains from other mods.

You're right! I guess I should 've search before asking but I'm not supposed to be doing this on this computer at work.

I've read that the hole is to be drilled in the flange. Is this the flange of the stat to the manifold? or the flange of the part that opens? I know this sounds stupid.

I drill one or two holes. When I drill two, I space them 180 degrees apart. I usually use a 1/16" bit. The one shown below is a 1/16". Don't get too far out towards the edge or the rubber gasket will block the hole. My concern is to provide an air bleed. I install the thermostat so that the drilled hole is in the highest position (12:00 O'Clock).

The GM 195 thermostat that I bought about a year ago for my 03 had a hole and that'* supposed to go at the top to let the air out. The Stant that I had bought a few months earlier did NOT have any apparent opening for an air bleed. But when any thermostat is fully open and the water pump circulate at a high engine speed any air is going to be expressed through and to the radiator and to the reserve tank.

Thanks to all who replied.
Got it.

I didn't realize where this was the first time...moved to General chat since this is not a mechanical problem.