[patrickt]

There all going to be "vented" in that when they reach their maximum pressure they will allow steam/coolant to blow out through the cap. Mine has done that when my fans failed. What a plain vented cap won't do is allow coolant to be sucked back in to the cooling system as it cools and contracts. That's where you need a coolant recovery type cap and a coolant recovery system (of which I have neither). If you are not sure whether or not you have a recovery type cap, the way you test it is with the "Putnam Suck Test" as outlined in the referenced thread.


EDIT -- They might be using the term "vented" to also mean they have the little lever on the top that lets you pull it and blow off steam as well.