Vented Radiator Cap / Partial Pressure Coolant System...

Guys,

As I understand, maybe all of the A-Body cars came with a Partial Pressure cooling system. I had never heard of it before, so maybe some of you guys haven't either.

It's determined simply by the radiator cap. A partial pressure coolant system has a radiator cap with a gravity controlled vent. Meaning, with a cool system, there's a vent that hangs open on the bottom of the radiator cap. And the coolant system will not build pressure until coolant warms up enough to touch the vent. The vent is closed by coolant as it rises (from heat) and pushes the vent closed.

At that point, pressure builds in the system and the radiator cap works in the way it does now, opening to vent out coolant to maintain a set pressure … set by the spring force of the radiator cap.

Nowadays, these vented caps aren't used much or at all (on new cars) to my knowledge. It's now full pressure coolant systems. Meaning, from the moment the coolant starts to warm, the pressure builds. I don't believe the current radiator cap on my Scamp is vented.

I will be changing the thermostat and radiator cap when I change intakes.

Does anyone here run a vented radiator cap? Summit sells one sure enough, it's part number SNN-10231.