Yeah, me too. But why on one and not the other?

 

it is a breather to let air escape through out the system. also if the factory stat goes it will still let fluid flow. now all stats are failsafe so if they go they will open up. but these are not like that when they go they stay shut.

 

Thanks for the info.

 

Thats correct it's a breather and if i were using the new one i would drill a small hole in that position on the new one, this keeps air pockets from forming in the system which can actualy stop the flow of water. I do this on my 66 t-bird thermostat otherwise an air pocket will form and cause it to get hot.